Re: [PATCH v3 12/46] kmsan: add KMSAN runtime core

From: Marco Elver
Date: Wed Apr 27 2022 - 10:10:17 EST

On Tue, Apr 26, 2022 at 06:42PM +0200, Alexander Potapenko wrote:
> For each memory location KernelMemorySanitizer maintains two types of
> metadata:
> 1. The so-called shadow of that location - а byte:byte mapping describing
> whether or not individual bits of memory are initialized (shadow is 0)
> or not (shadow is 1).
> 2. The origins of that location - а 4-byte:4-byte mapping containing
> 4-byte IDs of the stack traces where uninitialized values were
> created.
>
> Each struct page now contains pointers to two struct pages holding
> KMSAN metadata (shadow and origins) for the original struct page.
> Utility routines in mm/kmsan/core.c and mm/kmsan/shadow.c handle the
> metadata creation, addressing, copying and checking.
> mm/kmsan/report.c performs error reporting in the cases an uninitialized
> value is used in a way that leads to undefined behavior.
>
> KMSAN compiler instrumentation is responsible for tracking the metadata
> along with the kernel memory. mm/kmsan/instrumentation.c provides the
> implementation for instrumentation hooks that are called from files
> compiled with -fsanitize=kernel-memory.
>
> To aid parameter passing (also done at instrumentation level), each
> task_struct now contains a struct kmsan_task_state used to track the
> metadata of function parameters and return values for that task.
>
> Finally, this patch provides CONFIG_KMSAN that enables KMSAN, and
> declares CFLAGS_KMSAN, which are applied to files compiled with KMSAN.
> The KMSAN_SANITIZE:=n Makefile directive can be used to completely
> disable KMSAN instrumentation for certain files.
>
> Similarly, KMSAN_ENABLE_CHECKS:=n disables KMSAN checks and makes newly
> created stack memory initialized.
>
> Users can also use functions from include/linux/kmsan-checks.h to mark
> certain memory regions as uninitialized or initialized (this is called
> "poisoning" and "unpoisoning") or check that a particular region is
> initialized.
>
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> ---
> v2:
> -- as requested by Greg K-H, moved hooks for different subsystems to respective patches,
> rewrote the patch description;
> -- addressed comments by Dmitry Vyukov;
> -- added a note about KMSAN being not intended for production use.
> -- fix case of unaligned dst in kmsan_internal_memmove_metadata()
>
> v3:
> -- print build IDs in reports where applicable
> -- drop redundant filter_irq_stacks(), unpoison the local passed to __stack_depot_save()
> -- remove a stray BUG()
>
> Link: https://linux-review.googlesource.com/id/I9b71bfe3425466c97159f9de0062e5e8e4fec866
> ---
> Makefile | 1 +
> include/linux/kmsan-checks.h | 64 +++++
> include/linux/kmsan.h | 47 ++++
> include/linux/mm_types.h | 12 +
> include/linux/sched.h | 5 +
> lib/Kconfig.debug | 1 +
> lib/Kconfig.kmsan | 23 ++
> mm/Makefile | 1 +
> mm/kmsan/Makefile | 18 ++
> mm/kmsan/core.c | 458 +++++++++++++++++++++++++++++++++++
> mm/kmsan/hooks.c | 66 +++++
> mm/kmsan/instrumentation.c | 267 ++++++++++++++++++++
> mm/kmsan/kmsan.h | 183 ++++++++++++++
> mm/kmsan/report.c | 211 ++++++++++++++++
> mm/kmsan/shadow.c | 186 ++++++++++++++
> scripts/Makefile.kmsan | 1 +
> scripts/Makefile.lib | 9 +
> 17 files changed, 1553 insertions(+)
> create mode 100644 include/linux/kmsan-checks.h
> create mode 100644 include/linux/kmsan.h
> create mode 100644 lib/Kconfig.kmsan
> create mode 100644 mm/kmsan/Makefile
> create mode 100644 mm/kmsan/core.c
> create mode 100644 mm/kmsan/hooks.c
> create mode 100644 mm/kmsan/instrumentation.c
> create mode 100644 mm/kmsan/kmsan.h
> create mode 100644 mm/kmsan/report.c
> create mode 100644 mm/kmsan/shadow.c
> create mode 100644 scripts/Makefile.kmsan
>
> diff --git a/Makefile b/Makefile
> index c3ec1ea423797..d3c7dcd9f0fea 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1009,6 +1009,7 @@ include-y := scripts/Makefile.extrawarn
> include-$(CONFIG_DEBUG_INFO) += scripts/Makefile.debug
> include-$(CONFIG_KASAN) += scripts/Makefile.kasan
> include-$(CONFIG_KCSAN) += scripts/Makefile.kcsan
> +include-$(CONFIG_KMSAN) += scripts/Makefile.kmsan
> include-$(CONFIG_UBSAN) += scripts/Makefile.ubsan
> include-$(CONFIG_KCOV) += scripts/Makefile.kcov
> include-$(CONFIG_GCC_PLUGINS) += scripts/Makefile.gcc-plugins
> diff --git a/include/linux/kmsan-checks.h b/include/linux/kmsan-checks.h
> new file mode 100644
> index 0000000000000..a6522a0c28df9
> --- /dev/null
> +++ b/include/linux/kmsan-checks.h
> @@ -0,0 +1,64 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * KMSAN checks to be used for one-off annotations in subsystems.
> + *
> + * Copyright (C) 2017-2022 Google LLC
> + * Author: Alexander Potapenko <glider@xxxxxxxxxx>
> + *
> + */
> +
> +#ifndef _LINUX_KMSAN_CHECKS_H
> +#define _LINUX_KMSAN_CHECKS_H
> +
> +#include <linux/types.h>
> +
> +#ifdef CONFIG_KMSAN
> +
> +/**
> + * kmsan_poison_memory() - Mark the memory range as uninitialized.
> + * @address: address to start with.
> + * @size: size of buffer to poison.
> + * @flags: GFP flags for allocations done by this function.
> + *
> + * Until other data is written to this range, KMSAN will treat it as
> + * uninitialized. Error reports for this memory will reference the call site of
> + * kmsan_poison_memory() as origin.
> + */
> +void kmsan_poison_memory(const void *address, size_t size, gfp_t flags);
> +
> +/**
> + * kmsan_unpoison_memory() - Mark the memory range as initialized.
> + * @address: address to start with.
> + * @size: size of buffer to unpoison.
> + *
> + * Until other data is written to this range, KMSAN will treat it as
> + * initialized.
> + */
> +void kmsan_unpoison_memory(const void *address, size_t size);
> +
> +/**
> + * kmsan_check_memory() - Check the memory range for being initialized.
> + * @address: address to start with.
> + * @size: size of buffer to check.
> + *
> + * If any piece of the given range is marked as uninitialized, KMSAN will report
> + * an error.
> + */
> +void kmsan_check_memory(const void *address, size_t size);
> +
> +#else
> +
> +static inline void kmsan_poison_memory(const void *address, size_t size,
> + gfp_t flags)
> +{
> +}
> +static inline void kmsan_unpoison_memory(const void *address, size_t size)
> +{
> +}
> +static inline void kmsan_check_memory(const void *address, size_t size)
> +{
> +}
> +
> +#endif
> +
> +#endif /* _LINUX_KMSAN_CHECKS_H */
> diff --git a/include/linux/kmsan.h b/include/linux/kmsan.h
> new file mode 100644
> index 0000000000000..4e35f43eceaa9
> --- /dev/null
> +++ b/include/linux/kmsan.h
> @@ -0,0 +1,47 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * KMSAN API for subsystems.
> + *
> + * Copyright (C) 2017-2022 Google LLC
> + * Author: Alexander Potapenko <glider@xxxxxxxxxx>
> + *
> + */
> +#ifndef _LINUX_KMSAN_H
> +#define _LINUX_KMSAN_H
> +
> +#include <linux/gfp.h>
> +#include <linux/kmsan-checks.h>
> +#include <linux/stackdepot.h>
> +#include <linux/types.h>
> +#include <linux/vmalloc.h>
> +
> +struct page;
> +
> +#ifdef CONFIG_KMSAN
> +
> +/* These constants are defined in the MSan LLVM instrumentation pass. */
> +#define KMSAN_RETVAL_SIZE 800
> +#define KMSAN_PARAM_SIZE 800
> +
> +struct kmsan_context_state {
> + char param_tls[KMSAN_PARAM_SIZE];
> + char retval_tls[KMSAN_RETVAL_SIZE];
> + char va_arg_tls[KMSAN_PARAM_SIZE];
> + char va_arg_origin_tls[KMSAN_PARAM_SIZE];
> + u64 va_arg_overflow_size_tls;
> + char param_origin_tls[KMSAN_PARAM_SIZE];
> + depot_stack_handle_t retval_origin_tls;
> +};
> +
> +#undef KMSAN_PARAM_SIZE
> +#undef KMSAN_RETVAL_SIZE
> +
> +struct kmsan_ctx {
> + struct kmsan_context_state cstate;
> + int kmsan_in_runtime;
> + bool allow_reporting;
> +};
> +
> +#endif
> +
> +#endif /* _LINUX_KMSAN_H */
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 8834e38c06a4f..85c97a2145f7e 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -218,6 +218,18 @@ struct page {
> not kmapped, ie. highmem) */
> #endif /* WANT_PAGE_VIRTUAL */
>
> +#ifdef CONFIG_KMSAN
> + /*
> + * KMSAN metadata for this page:
> + * - shadow page: every bit indicates whether the corresponding
> + * bit of the original page is initialized (0) or not (1);
> + * - origin page: every 4 bytes contain an id of the stack trace
> + * where the uninitialized value was created.
> + */
> + struct page *kmsan_shadow;
> + struct page *kmsan_origin;
> +#endif
> +
> #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
> int _last_cpupid;
> #endif
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index a8911b1f35aad..9e53624cd73ac 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -14,6 +14,7 @@
> #include <linux/pid.h>
> #include <linux/sem.h>
> #include <linux/shm.h>
> +#include <linux/kmsan.h>
> #include <linux/mutex.h>
> #include <linux/plist.h>
> #include <linux/hrtimer.h>
> @@ -1352,6 +1353,10 @@ struct task_struct {
> #endif
> #endif
>
> +#ifdef CONFIG_KMSAN
> + struct kmsan_ctx kmsan_ctx;
> +#endif
> +
> #if IS_ENABLED(CONFIG_KUNIT)
> struct kunit *kunit_test;
> #endif
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 075cd25363ac3..b81670878acae 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -996,6 +996,7 @@ config DEBUG_STACKOVERFLOW
>
> source "lib/Kconfig.kasan"
> source "lib/Kconfig.kfence"
> +source "lib/Kconfig.kmsan"
>
> endmenu # "Memory Debugging"
>
> diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
> new file mode 100644
> index 0000000000000..199f79d031f94
> --- /dev/null
> +++ b/lib/Kconfig.kmsan
> @@ -0,0 +1,23 @@

Missing SPDX-License-Identifier.

> +config HAVE_ARCH_KMSAN
> + bool
> +
> +config HAVE_KMSAN_COMPILER
> + def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=kernel-memory -mllvm -msan-disable-checks=1))
> +
> +config KMSAN
> + bool "KMSAN: detector of uninitialized values use"
> + depends on HAVE_ARCH_KMSAN && HAVE_KMSAN_COMPILER
> + depends on SLUB && DEBUG_KERNEL && !KASAN && !KCSAN
> + depends on CC_IS_CLANG && CLANG_VERSION >= 140000

Shouldn't the "CC_IS_CLANG && CLANG_VERSION ..." check be a "depends on"
in HAVE_KMSAN_COMPILER? That way all the compiler-related checks are
confined to HAVE_KMSAN_COMPILER.

I guess, it might also be worth mentioning why the version check is
required at all (something about older compilers supporting
fsanitize=kernel-memory, but not having all features we need).

> + select STACKDEPOT
> + select STACKDEPOT_ALWAYS_INIT
> + help
> + KernelMemorySanitizer (KMSAN) is a dynamic detector of uses of
> + uninitialized values in the kernel. It is based on compiler
> + instrumentation provided by Clang and thus requires Clang to build.
> +
> + An important note is that KMSAN is not intended for production use,
> + because it drastically increases kernel memory footprint and slows
> + the whole system down.
> +
> + See <file:Documentation/dev-tools/kmsan.rst> for more details.
> diff --git a/mm/Makefile b/mm/Makefile
> index 4cc13f3179a51..4da7eeaecc214 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -89,6 +89,7 @@ obj-$(CONFIG_SLAB) += slab.o
> obj-$(CONFIG_SLUB) += slub.o
> obj-$(CONFIG_KASAN) += kasan/
> obj-$(CONFIG_KFENCE) += kfence/
> +obj-$(CONFIG_KMSAN) += kmsan/
> obj-$(CONFIG_FAILSLAB) += failslab.o
> obj-$(CONFIG_MEMTEST) += memtest.o
> obj-$(CONFIG_MIGRATION) += migrate.o
> diff --git a/mm/kmsan/Makefile b/mm/kmsan/Makefile
> new file mode 100644
> index 0000000000000..a80dde1de7048
> --- /dev/null
> +++ b/mm/kmsan/Makefile
> @@ -0,0 +1,18 @@

Makefile needs a SPDX-License-Identifier.

> +obj-y := core.o instrumentation.o hooks.o report.o shadow.o
> +
> +KMSAN_SANITIZE := n
> +KCOV_INSTRUMENT := n
> +UBSAN_SANITIZE := n
> +
> +# Disable instrumentation of KMSAN runtime with other tools.
> +CC_FLAGS_KMSAN_RUNTIME := -fno-stack-protector
> +CC_FLAGS_KMSAN_RUNTIME += $(call cc-option,-fno-conserve-stack)
> +CC_FLAGS_KMSAN_RUNTIME += -DDISABLE_BRANCH_PROFILING
> +
> +CFLAGS_REMOVE.o = $(CC_FLAGS_FTRACE)
> +
> +CFLAGS_core.o := $(CC_FLAGS_KMSAN_RUNTIME)
> +CFLAGS_hooks.o := $(CC_FLAGS_KMSAN_RUNTIME)
> +CFLAGS_instrumentation.o := $(CC_FLAGS_KMSAN_RUNTIME)
> +CFLAGS_report.o := $(CC_FLAGS_KMSAN_RUNTIME)
> +CFLAGS_shadow.o := $(CC_FLAGS_KMSAN_RUNTIME)
> diff --git a/mm/kmsan/core.c b/mm/kmsan/core.c
> new file mode 100644
> index 0000000000000..933d864d9d467
> --- /dev/null
> +++ b/mm/kmsan/core.c
> @@ -0,0 +1,458 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KMSAN runtime library.
> + *
> + * Copyright (C) 2017-2022 Google LLC
> + * Author: Alexander Potapenko <glider@xxxxxxxxxx>
> + *
> + */
> +
> +#include <asm/page.h>
> +#include <linux/compiler.h>
> +#include <linux/export.h>
> +#include <linux/highmem.h>
> +#include <linux/interrupt.h>
> +#include <linux/kernel.h>
> +#include <linux/kmsan.h>
> +#include <linux/memory.h>
> +#include <linux/mm.h>
> +#include <linux/mm_types.h>
> +#include <linux/mmzone.h>
> +#include <linux/percpu-defs.h>
> +#include <linux/preempt.h>
> +#include <linux/slab.h>
> +#include <linux/stackdepot.h>
> +#include <linux/stacktrace.h>
> +#include <linux/types.h>
> +#include <linux/vmalloc.h>
> +
> +#include "../slab.h"
> +#include "kmsan.h"
> +
> +/*
> + * Avoid creating too long origin chains, these are unlikely to participate in
> + * real reports.
> + */
> +#define MAX_CHAIN_DEPTH 7
> +#define NUM_SKIPPED_TO_WARN 10000
> +
> +bool kmsan_enabled __read_mostly;
> +
> +/*
> + * Per-CPU KMSAN context to be used in interrupts, where current->kmsan is
> + * unavaliable.
> + */
> +DEFINE_PER_CPU(struct kmsan_ctx, kmsan_percpu_ctx);
> +
> +void kmsan_internal_poison_memory(void *address, size_t size, gfp_t flags,
> + unsigned int poison_flags)
> +{
> + u32 extra_bits =
> + kmsan_extra_bits(/*depth*/ 0, poison_flags & KMSAN_POISON_FREE);
> + bool checked = poison_flags & KMSAN_POISON_CHECK;
> + depot_stack_handle_t handle;
> +
> + handle = kmsan_save_stack_with_flags(flags, extra_bits);
> + kmsan_internal_set_shadow_origin(address, size, -1, handle, checked);
> +}
> +
> +void kmsan_internal_unpoison_memory(void *address, size_t size, bool checked)
> +{
> + kmsan_internal_set_shadow_origin(address, size, 0, 0, checked);
> +}
> +
> +depot_stack_handle_t kmsan_save_stack_with_flags(gfp_t flags,
> + unsigned int extra)
> +{
> + unsigned long entries[KMSAN_STACK_DEPTH];
> + unsigned int nr_entries;
> +
> + nr_entries = stack_trace_save(entries, KMSAN_STACK_DEPTH, 0);
> +
> + /* Don't sleep (see might_sleep_if() in __alloc_pages_nodemask()). */
> + flags &= ~__GFP_DIRECT_RECLAIM;
> +
> + return __stack_depot_save(entries, nr_entries, extra, flags, true);
> +}
> +
> +/* Copy the metadata following the memmove() behavior. */
> +void kmsan_internal_memmove_metadata(void *dst, void *src, size_t n)
> +{
> + depot_stack_handle_t old_origin = 0, new_origin = 0;
> + int src_slots, dst_slots, i, iter, step, skip_bits;
> + depot_stack_handle_t *origin_src, *origin_dst;
> + void *shadow_src, *shadow_dst;
> + u32 *align_shadow_src, shadow;
> + bool backwards;
> +
> + shadow_dst = kmsan_get_metadata(dst, KMSAN_META_SHADOW);
> + if (!shadow_dst)
> + return;
> + KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(dst, n));
> +
> + shadow_src = kmsan_get_metadata(src, KMSAN_META_SHADOW);
> + if (!shadow_src) {
> + /*
> + * |src| is untracked: zero out destination shadow, ignore the

Probably doesn't matter too much, but for consistency elsewhere - @src?

> + * origins, we're done.
> + */
> + __memset(shadow_dst, 0, n);
> + return;
> + }
> + KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(src, n));
> +
> + __memmove(shadow_dst, shadow_src, n);
> +
> + origin_dst = kmsan_get_metadata(dst, KMSAN_META_ORIGIN);
> + origin_src = kmsan_get_metadata(src, KMSAN_META_ORIGIN);
> + KMSAN_WARN_ON(!origin_dst || !origin_src);
> + src_slots = (ALIGN((u64)src + n, KMSAN_ORIGIN_SIZE) -
> + ALIGN_DOWN((u64)src, KMSAN_ORIGIN_SIZE)) /
> + KMSAN_ORIGIN_SIZE;
> + dst_slots = (ALIGN((u64)dst + n, KMSAN_ORIGIN_SIZE) -
> + ALIGN_DOWN((u64)dst, KMSAN_ORIGIN_SIZE)) /
> + KMSAN_ORIGIN_SIZE;
> + KMSAN_WARN_ON((src_slots < 1) || (dst_slots < 1));
> + KMSAN_WARN_ON((src_slots - dst_slots > 1) ||
> + (dst_slots - src_slots < -1));
> +
> + backwards = dst > src;
> + i = backwards ? min(src_slots, dst_slots) - 1 : 0;
> + iter = backwards ? -1 : 1;
> +
> + align_shadow_src =
> + (u32 *)ALIGN_DOWN((u64)shadow_src, KMSAN_ORIGIN_SIZE);
> + for (step = 0; step < min(src_slots, dst_slots); step++, i += iter) {
> + KMSAN_WARN_ON(i < 0);
> + shadow = align_shadow_src[i];
> + if (i == 0) {
> + /*
> + * If |src| isn't aligned on KMSAN_ORIGIN_SIZE, don't
> + * look at the first |src % KMSAN_ORIGIN_SIZE| bytes
> + * of the first shadow slot.
> + */
> + skip_bits = ((u64)src % KMSAN_ORIGIN_SIZE) * 8;
> + shadow = (shadow >> skip_bits) << skip_bits;
> + }
> + if (i == src_slots - 1) {
> + /*
> + * If |src + n| isn't aligned on
> + * KMSAN_ORIGIN_SIZE, don't look at the last
> + * |(src + n) % KMSAN_ORIGIN_SIZE| bytes of the
> + * last shadow slot.
> + */
> + skip_bits = (((u64)src + n) % KMSAN_ORIGIN_SIZE) * 8;
> + shadow = (shadow << skip_bits) >> skip_bits;
> + }
> + /*
> + * Overwrite the origin only if the corresponding
> + * shadow is nonempty.
> + */
> + if (origin_src[i] && (origin_src[i] != old_origin) && shadow) {
> + old_origin = origin_src[i];
> + new_origin = kmsan_internal_chain_origin(old_origin);
> + /*
> + * kmsan_internal_chain_origin() may return
> + * NULL, but we don't want to lose the previous
> + * origin value.
> + */
> + if (!new_origin)
> + new_origin = old_origin;
> + }
> + if (shadow)
> + origin_dst[i] = new_origin;
> + else
> + origin_dst[i] = 0;
> + }
> + /*
> + * If dst_slots is greater than src_slots (i.e.
> + * dst_slots == src_slots + 1), there is an extra origin slot at the
> + * beginning or end of the destination buffer, for which we take the
> + * origin from the previous slot.
> + * This is only done if the part of the source shadow corresponding to
> + * slot is non-zero.
> + *
> + * E.g. if we copy 8 aligned bytes that are marked as uninitialized
> + * and have origins o111 and o222, to an unaligned buffer with offset 1,
> + * these two origins are copied to three origin slots, so one of then
> + * needs to be duplicated, depending on the copy direction (@backwards)
> + *
> + * src shadow: |uuuu|uuuu|....|
> + * src origin: |o111|o222|....|
> + *
> + * backwards = 0:
> + * dst shadow: |.uuu|uuuu|u...|
> + * dst origin: |....|o111|o222| - fill the empty slot with o111
> + * backwards = 1:
> + * dst shadow: |.uuu|uuuu|u...|
> + * dst origin: |o111|o222|....| - fill the empty slot with o222
> + */
> + if (src_slots < dst_slots) {
> + if (backwards) {
> + shadow = align_shadow_src[src_slots - 1];
> + skip_bits = (((u64)dst + n) % KMSAN_ORIGIN_SIZE) * 8;
> + shadow = (shadow << skip_bits) >> skip_bits;
> + if (shadow)
> + /* src_slots > 0, therefore dst_slots is at least 2 */
> + origin_dst[dst_slots - 1] = origin_dst[dst_slots - 2];
> + } else {
> + shadow = align_shadow_src[0];
> + skip_bits = ((u64)dst % KMSAN_ORIGIN_SIZE) * 8;
> + shadow = (shadow >> skip_bits) << skip_bits;
> + if (shadow)
> + origin_dst[0] = origin_dst[1];
> + }
> + }
> +}
> +
> +depot_stack_handle_t kmsan_internal_chain_origin(depot_stack_handle_t id)
> +{
> + unsigned long entries[3];
> + u32 extra_bits;
> + int depth;
> + bool uaf;
> +
> + if (!id)
> + return id;
> + /*
> + * Make sure we have enough spare bits in |id| to hold the UAF bit and
> + * the chain depth.
> + */
> + BUILD_BUG_ON((1 << STACK_DEPOT_EXTRA_BITS) <= (MAX_CHAIN_DEPTH << 1));
> +
> + extra_bits = stack_depot_get_extra_bits(id);
> + depth = kmsan_depth_from_eb(extra_bits);
> + uaf = kmsan_uaf_from_eb(extra_bits);
> +
> + if (depth >= MAX_CHAIN_DEPTH) {
> + static atomic_long_t kmsan_skipped_origins;
> + long skipped = atomic_long_inc_return(&kmsan_skipped_origins);
> +
> + if (skipped % NUM_SKIPPED_TO_WARN == 0) {
> + pr_warn("not chained %ld origins\n", skipped);
> + dump_stack();
> + kmsan_print_origin(id);
> + }
> + return id;
> + }
> + depth++;
> + extra_bits = kmsan_extra_bits(depth, uaf);
> +
> + entries[0] = KMSAN_CHAIN_MAGIC_ORIGIN;
> + entries[1] = kmsan_save_stack_with_flags(GFP_ATOMIC, 0);
> + entries[2] = id;
> + /*
> + * @entries is a local var in non-instrumented code, so KMSAN does not
> + * know it is initialized. Explicitly unpoison it to avoid false
> + * positives when __stack_depot_save() passes it to instrumented code.
> + */
> + kmsan_internal_unpoison_memory(entries, sizeof(entries), false);
> + return __stack_depot_save(entries, ARRAY_SIZE(entries), extra_bits,
> + GFP_ATOMIC, true);
> +}
> +
> +void kmsan_internal_set_shadow_origin(void *addr, size_t size, int b,
> + u32 origin, bool checked)
> +{
> + u64 address = (u64)addr;
> + void *shadow_start;
> + u32 *origin_start;
> + size_t pad = 0;
> + int i;
> +
> + KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(addr, size));
> + shadow_start = kmsan_get_metadata(addr, KMSAN_META_SHADOW);
> + if (!shadow_start) {
> + /*
> + * kmsan_metadata_is_contiguous() is true, so either all shadow
> + * and origin pages are NULL, or all are non-NULL.
> + */
> + if (checked) {
> + pr_err("%s: not memsetting %ld bytes starting at %px, because the shadow is NULL\n",
> + __func__, size, addr);
> + KMSAN_WARN_ON(true);
> + }
> + return;
> + }
> + __memset(shadow_start, b, size);
> +
> + if (!IS_ALIGNED(address, KMSAN_ORIGIN_SIZE)) {
> + pad = address % KMSAN_ORIGIN_SIZE;
> + address -= pad;
> + size += pad;
> + }
> + size = ALIGN(size, KMSAN_ORIGIN_SIZE);
> + origin_start =
> + (u32 *)kmsan_get_metadata((void *)address, KMSAN_META_ORIGIN);
> +
> + for (i = 0; i < size / KMSAN_ORIGIN_SIZE; i++)
> + origin_start[i] = origin;
> +}
> +
> +struct page *kmsan_vmalloc_to_page_or_null(void *vaddr)
> +{
> + struct page *page;
> +
> + if (!kmsan_internal_is_vmalloc_addr(vaddr) &&
> + !kmsan_internal_is_module_addr(vaddr))
> + return NULL;
> + page = vmalloc_to_page(vaddr);
> + if (pfn_valid(page_to_pfn(page)))
> + return page;
> + else
> + return NULL;
> +}
> +
> +void kmsan_internal_check_memory(void *addr, size_t size, const void *user_addr,
> + int reason)
> +{
> + depot_stack_handle_t cur_origin = 0, new_origin = 0;
> + unsigned long addr64 = (unsigned long)addr;
> + depot_stack_handle_t *origin = NULL;
> + unsigned char *shadow = NULL;
> + int cur_off_start = -1;
> + int i, chunk_size;
> + size_t pos = 0;
> +
> + if (!size)
> + return;
> + KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(addr, size));
> + while (pos < size) {
> + chunk_size = min(size - pos,
> + PAGE_SIZE - ((addr64 + pos) % PAGE_SIZE));
> + shadow = kmsan_get_metadata((void *)(addr64 + pos),
> + KMSAN_META_SHADOW);
> + if (!shadow) {
> + /*
> + * This page is untracked. If there were uninitialized
> + * bytes before, report them.
> + */
> + if (cur_origin) {
> + kmsan_enter_runtime();
> + kmsan_report(cur_origin, addr, size,
> + cur_off_start, pos - 1, user_addr,
> + reason);
> + kmsan_leave_runtime();
> + }
> + cur_origin = 0;
> + cur_off_start = -1;
> + pos += chunk_size;
> + continue;
> + }
> + for (i = 0; i < chunk_size; i++) {
> + if (!shadow[i]) {
> + /*
> + * This byte is unpoisoned. If there were
> + * poisoned bytes before, report them.
> + */
> + if (cur_origin) {
> + kmsan_enter_runtime();
> + kmsan_report(cur_origin, addr, size,
> + cur_off_start, pos + i - 1,
> + user_addr, reason);
> + kmsan_leave_runtime();
> + }
> + cur_origin = 0;
> + cur_off_start = -1;
> + continue;
> + }
> + origin = kmsan_get_metadata((void *)(addr64 + pos + i),
> + KMSAN_META_ORIGIN);
> + KMSAN_WARN_ON(!origin);
> + new_origin = *origin;
> + /*
> + * Encountered new origin - report the previous
> + * uninitialized range.
> + */
> + if (cur_origin != new_origin) {
> + if (cur_origin) {
> + kmsan_enter_runtime();
> + kmsan_report(cur_origin, addr, size,
> + cur_off_start, pos + i - 1,
> + user_addr, reason);
> + kmsan_leave_runtime();
> + }
> + cur_origin = new_origin;
> + cur_off_start = pos + i;
> + }
> + }
> + pos += chunk_size;
> + }
> + KMSAN_WARN_ON(pos != size);
> + if (cur_origin) {
> + kmsan_enter_runtime();
> + kmsan_report(cur_origin, addr, size, cur_off_start, pos - 1,
> + user_addr, reason);
> + kmsan_leave_runtime();
> + }
> +}
> +
> +bool kmsan_metadata_is_contiguous(void *addr, size_t size)
> +{
> + char *cur_shadow = NULL, *next_shadow = NULL, *cur_origin = NULL,
> + *next_origin = NULL;
> + u64 cur_addr = (u64)addr, next_addr = cur_addr + PAGE_SIZE;
> + depot_stack_handle_t *origin_p;
> + bool all_untracked = false;
> +
> + if (!size)
> + return true;
> +
> + /* The whole range belongs to the same page. */
> + if (ALIGN_DOWN(cur_addr + size - 1, PAGE_SIZE) ==
> + ALIGN_DOWN(cur_addr, PAGE_SIZE))
> + return true;
> +
> + cur_shadow = kmsan_get_metadata((void *)cur_addr, /*is_origin*/ false);
> + if (!cur_shadow)
> + all_untracked = true;
> + cur_origin = kmsan_get_metadata((void *)cur_addr, /*is_origin*/ true);
> + if (all_untracked && cur_origin)
> + goto report;
> +
> + for (; next_addr < (u64)addr + size;
> + cur_addr = next_addr, cur_shadow = next_shadow,
> + cur_origin = next_origin, next_addr += PAGE_SIZE) {
> + next_shadow = kmsan_get_metadata((void *)next_addr, false);
> + next_origin = kmsan_get_metadata((void *)next_addr, true);
> + if (all_untracked) {
> + if (next_shadow || next_origin)
> + goto report;
> + if (!next_shadow && !next_origin)
> + continue;
> + }
> + if (((u64)cur_shadow == ((u64)next_shadow - PAGE_SIZE)) &&
> + ((u64)cur_origin == ((u64)next_origin - PAGE_SIZE)))
> + continue;
> + goto report;
> + }
> + return true;
> +
> +report:
> + pr_err("%s: attempting to access two shadow page ranges.\n", __func__);
> + pr_err("Access of size %ld at %px.\n", size, addr);
> + pr_err("Addresses belonging to different ranges: %px and %px\n",
> + (void *)cur_addr, (void *)next_addr);
> + pr_err("page[0].shadow: %px, page[1].shadow: %px\n", cur_shadow,
> + next_shadow);
> + pr_err("page[0].origin: %px, page[1].origin: %px\n", cur_origin,
> + next_origin);
> + origin_p = kmsan_get_metadata(addr, KMSAN_META_ORIGIN);
> + if (origin_p) {
> + pr_err("Origin: %08x\n", *origin_p);
> + kmsan_print_origin(*origin_p);
> + } else {
> + pr_err("Origin: unavailable\n");
> + }
> + return false;
> +}
> +
> +bool kmsan_internal_is_module_addr(void *vaddr)
> +{
> + return ((u64)vaddr >= MODULES_VADDR) && ((u64)vaddr < MODULES_END);
> +}
> +
> +bool kmsan_internal_is_vmalloc_addr(void *addr)
> +{
> + return ((u64)addr >= VMALLOC_START) && ((u64)addr < VMALLOC_END);
> +}
> diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
> new file mode 100644
> index 0000000000000..4ac62fa67a02a
> --- /dev/null
> +++ b/mm/kmsan/hooks.c
> @@ -0,0 +1,66 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KMSAN hooks for kernel subsystems.
> + *
> + * These functions handle creation of KMSAN metadata for memory allocations.
> + *
> + * Copyright (C) 2018-2022 Google LLC
> + * Author: Alexander Potapenko <glider@xxxxxxxxxx>
> + *
> + */
> +
> +#include <linux/cacheflush.h>
> +#include <linux/gfp.h>
> +#include <linux/mm.h>
> +#include <linux/mm_types.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +
> +#include "../internal.h"
> +#include "../slab.h"
> +#include "kmsan.h"
> +
> +/*
> + * Instrumented functions shouldn't be called under
> + * kmsan_enter_runtime()/kmsan_leave_runtime(), because this will lead to
> + * skipping effects of functions like memset() inside instrumented code.
> + */
> +
> +/* Functions from kmsan-checks.h follow. */
> +void kmsan_poison_memory(const void *address, size_t size, gfp_t flags)
> +{
> + if (!kmsan_enabled || kmsan_in_runtime())
> + return;
> + kmsan_enter_runtime();
> + /* The users may want to poison/unpoison random memory. */
> + kmsan_internal_poison_memory((void *)address, size, flags,
> + KMSAN_POISON_NOCHECK);
> + kmsan_leave_runtime();
> +}
> +EXPORT_SYMBOL(kmsan_poison_memory);
> +
> +void kmsan_unpoison_memory(const void *address, size_t size)
> +{
> + unsigned long ua_flags;
> +
> + if (!kmsan_enabled || kmsan_in_runtime())
> + return;
> +
> + ua_flags = user_access_save();
> + kmsan_enter_runtime();
> + /* The users may want to poison/unpoison random memory. */
> + kmsan_internal_unpoison_memory((void *)address, size,
> + KMSAN_POISON_NOCHECK);
> + kmsan_leave_runtime();
> + user_access_restore(ua_flags);
> +}
> +EXPORT_SYMBOL(kmsan_unpoison_memory);
> +
> +void kmsan_check_memory(const void *addr, size_t size)
> +{
> + if (!kmsan_enabled)
> + return;
> + return kmsan_internal_check_memory((void *)addr, size, /*user_addr*/ 0,
> + REASON_ANY);
> +}
> +EXPORT_SYMBOL(kmsan_check_memory);
> diff --git a/mm/kmsan/instrumentation.c b/mm/kmsan/instrumentation.c
> new file mode 100644
> index 0000000000000..fe062d123a76f
> --- /dev/null
> +++ b/mm/kmsan/instrumentation.c
> @@ -0,0 +1,267 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KMSAN compiler API.
> + *
> + * This file implements __msan_XXX hooks that Clang inserts into the code
> + * compiled with -fsanitize=kernel-memory.
> + * See Documentation/dev-tools/kmsan.rst for more information on how KMSAN
> + * instrumentation works.
> + *
> + * Copyright (C) 2017-2022 Google LLC
> + * Author: Alexander Potapenko <glider@xxxxxxxxxx>
> + *
> + */
> +
> +#include "kmsan.h"
> +#include <linux/gfp.h>
> +#include <linux/mm.h>
> +#include <linux/uaccess.h>
> +
> +static inline bool is_bad_asm_addr(void *addr, uintptr_t size, bool is_store)
> +{
> + if ((u64)addr < TASK_SIZE)
> + return true;
> + if (!kmsan_get_metadata(addr, KMSAN_META_SHADOW))
> + return true;
> + return false;
> +}
> +
> +static inline struct shadow_origin_ptr
> +get_shadow_origin_ptr(void *addr, u64 size, bool store)
> +{
> + unsigned long ua_flags = user_access_save();
> + struct shadow_origin_ptr ret;
> +
> + ret = kmsan_get_shadow_origin_ptr(addr, size, store);
> + user_access_restore(ua_flags);
> + return ret;
> +}
> +
> +/* Get shadow and origin pointers for a memory load with non-standard size. */
> +struct shadow_origin_ptr __msan_metadata_ptr_for_load_n(void *addr,
> + uintptr_t size)
> +{
> + return get_shadow_origin_ptr(addr, size, /*store*/ false);
> +}
> +EXPORT_SYMBOL(__msan_metadata_ptr_for_load_n);
> +
> +/* Get shadow and origin pointers for a memory store with non-standard size. */
> +struct shadow_origin_ptr __msan_metadata_ptr_for_store_n(void *addr,
> + uintptr_t size)
> +{
> + return get_shadow_origin_ptr(addr, size, /*store*/ true);
> +}
> +EXPORT_SYMBOL(__msan_metadata_ptr_for_store_n);
> +
> +/*
> + * Declare functions that obtain shadow/origin pointers for loads and stores
> + * with fixed size.
> + */
> +#define DECLARE_METADATA_PTR_GETTER(size) \
> + struct shadow_origin_ptr __msan_metadata_ptr_for_load_##size( \
> + void *addr) \
> + { \
> + return get_shadow_origin_ptr(addr, size, /*store*/ false); \
> + } \
> + EXPORT_SYMBOL(__msan_metadata_ptr_for_load_##size); \
> + struct shadow_origin_ptr __msan_metadata_ptr_for_store_##size( \
> + void *addr) \
> + { \
> + return get_shadow_origin_ptr(addr, size, /*store*/ true); \
> + } \
> + EXPORT_SYMBOL(__msan_metadata_ptr_for_store_##size)
> +
> +DECLARE_METADATA_PTR_GETTER(1);
> +DECLARE_METADATA_PTR_GETTER(2);
> +DECLARE_METADATA_PTR_GETTER(4);
> +DECLARE_METADATA_PTR_GETTER(8);
> +
> +/*
> + * Handle a memory store performed by inline assembly. KMSAN conservatively
> + * attempts to unpoison the outputs of asm() directives to prevent false
> + * positives caused by missed stores.
> + */
> +void __msan_instrument_asm_store(void *addr, uintptr_t size)
> +{
> + unsigned long ua_flags;
> +
> + if (!kmsan_enabled || kmsan_in_runtime())
> + return;
> +
> + ua_flags = user_access_save();
> + /*
> + * Most of the accesses are below 32 bytes. The two exceptions so far
> + * are clwb() (64 bytes) and FPU state (512 bytes).
> + * It's unlikely that the assembly will touch more than 512 bytes.
> + */
> + if (size > 512) {
> + WARN_ONCE(1, "assembly store size too big: %ld\n", size);
> + size = 8;
> + }
> + if (is_bad_asm_addr(addr, size, /*is_store*/ true)) {
> + user_access_restore(ua_flags);
> + return;
> + }
> + kmsan_enter_runtime();
> + /* Unpoisoning the memory on best effort. */
> + kmsan_internal_unpoison_memory(addr, size, /*checked*/ false);
> + kmsan_leave_runtime();
> + user_access_restore(ua_flags);
> +}
> +EXPORT_SYMBOL(__msan_instrument_asm_store);
> +
> +/* Handle llvm.memmove intrinsic. */
> +void *__msan_memmove(void *dst, const void *src, uintptr_t n)
> +{
> + void *result;
> +
> + result = __memmove(dst, src, n);
> + if (!n)
> + /* Some people call memmove() with zero length. */
> + return result;
> + if (!kmsan_enabled || kmsan_in_runtime())
> + return result;
> +
> + kmsan_internal_memmove_metadata(dst, (void *)src, n);
> +
> + return result;
> +}
> +EXPORT_SYMBOL(__msan_memmove);
> +
> +/* Handle llvm.memcpy intrinsic. */
> +void *__msan_memcpy(void *dst, const void *src, uintptr_t n)
> +{
> + void *result;
> +
> + result = __memcpy(dst, src, n);
> + if (!n)
> + /* Some people call memcpy() with zero length. */
> + return result;
> +
> + if (!kmsan_enabled || kmsan_in_runtime())
> + return result;
> +
> + /* Using memmove instead of memcpy doesn't affect correctness. */
> + kmsan_internal_memmove_metadata(dst, (void *)src, n);
> +
> + return result;
> +}
> +EXPORT_SYMBOL(__msan_memcpy);
> +
> +/* Handle llvm.memset intrinsic. */
> +void *__msan_memset(void *dst, int c, uintptr_t n)
> +{
> + void *result;
> +
> + result = __memset(dst, c, n);
> + if (!kmsan_enabled || kmsan_in_runtime())
> + return result;
> +
> + kmsan_enter_runtime();
> + /*
> + * Clang doesn't pass parameter metadata here, so it is impossible to
> + * use shadow of @c to set up the shadow for @dst.
> + */
> + kmsan_internal_unpoison_memory(dst, n, /*checked*/ false);
> + kmsan_leave_runtime();
> +
> + return result;
> +}
> +EXPORT_SYMBOL(__msan_memset);
> +
> +/*
> + * Create a new origin from an old one. This is done when storing an
> + * uninitialized value to memory. When reporting an error, KMSAN unrolls and
> + * prints the whole chain of stores that preceded the use of this value.
> + */
> +depot_stack_handle_t __msan_chain_origin(depot_stack_handle_t origin)
> +{
> + depot_stack_handle_t ret = 0;
> + unsigned long ua_flags;
> +
> + if (!kmsan_enabled || kmsan_in_runtime())
> + return ret;
> +
> + ua_flags = user_access_save();
> +
> + /* Creating new origins may allocate memory. */
> + kmsan_enter_runtime();
> + ret = kmsan_internal_chain_origin(origin);
> + kmsan_leave_runtime();
> + user_access_restore(ua_flags);
> + return ret;
> +}
> +EXPORT_SYMBOL(__msan_chain_origin);
> +
> +/* Poison a local variable when entering a function. */
> +void __msan_poison_alloca(void *address, uintptr_t size, char *descr)
> +{
> + depot_stack_handle_t handle;
> + unsigned long entries[4];
> + unsigned long ua_flags;
> +
> + if (!kmsan_enabled || kmsan_in_runtime())
> + return;
> +
> + ua_flags = user_access_save();
> + entries[0] = KMSAN_ALLOCA_MAGIC_ORIGIN;
> + entries[1] = (u64)descr;
> + entries[2] = (u64)__builtin_return_address(0);
> + /*
> + * With frame pointers enabled, it is possible to quickly fetch the
> + * second frame of the caller stack without calling the unwinder.
> + * Without them, simply do not bother.
> + */
> + if (IS_ENABLED(CONFIG_UNWINDER_FRAME_POINTER))
> + entries[3] = (u64)__builtin_return_address(1);
> + else
> + entries[3] = 0;
> +
> + /* stack_depot_save() may allocate memory. */
> + kmsan_enter_runtime();
> + handle = stack_depot_save(entries, ARRAY_SIZE(entries), GFP_ATOMIC);
> + kmsan_leave_runtime();
> +
> + kmsan_internal_set_shadow_origin(address, size, -1, handle,
> + /*checked*/ true);
> + user_access_restore(ua_flags);
> +}
> +EXPORT_SYMBOL(__msan_poison_alloca);
> +
> +/* Unpoison a local variable. */
> +void __msan_unpoison_alloca(void *address, uintptr_t size)
> +{
> + if (!kmsan_enabled || kmsan_in_runtime())
> + return;
> +
> + kmsan_enter_runtime();
> + kmsan_internal_unpoison_memory(address, size, /*checked*/ true);
> + kmsan_leave_runtime();
> +}
> +EXPORT_SYMBOL(__msan_unpoison_alloca);
> +
> +/*
> + * Report that an uninitialized value with the given origin was used in a way
> + * that constituted undefined behavior.
> + */
> +void __msan_warning(u32 origin)
> +{
> + if (!kmsan_enabled || kmsan_in_runtime())
> + return;
> + kmsan_enter_runtime();
> + kmsan_report(origin, /*address*/ 0, /*size*/ 0,
> + /*off_first*/ 0, /*off_last*/ 0, /*user_addr*/ 0,
> + REASON_ANY);
> + kmsan_leave_runtime();
> +}
> +EXPORT_SYMBOL(__msan_warning);
> +
> +/*
> + * At the beginning of an instrumented function, obtain the pointer to
> + * `struct kmsan_context_state` holding the metadata for function parameters.
> + */
> +struct kmsan_context_state *__msan_get_context_state(void)
> +{
> + return &kmsan_get_context()->cstate;
> +}
> +EXPORT_SYMBOL(__msan_get_context_state);
> diff --git a/mm/kmsan/kmsan.h b/mm/kmsan/kmsan.h
> new file mode 100644
> index 0000000000000..bfe38789950a6
> --- /dev/null
> +++ b/mm/kmsan/kmsan.h
> @@ -0,0 +1,183 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Functions used by the KMSAN runtime.
> + *
> + * Copyright (C) 2017-2022 Google LLC
> + * Author: Alexander Potapenko <glider@xxxxxxxxxx>
> + *
> + */
> +
> +#ifndef __MM_KMSAN_KMSAN_H
> +#define __MM_KMSAN_KMSAN_H
> +
> +#include <asm/pgtable_64_types.h>
> +#include <linux/irqflags.h>
> +#include <linux/sched.h>
> +#include <linux/stackdepot.h>
> +#include <linux/stacktrace.h>
> +#include <linux/nmi.h>
> +#include <linux/mm.h>
> +#include <linux/printk.h>
> +
> +#define KMSAN_ALLOCA_MAGIC_ORIGIN 0xabcd0100
> +#define KMSAN_CHAIN_MAGIC_ORIGIN 0xabcd0200
> +
> +#define KMSAN_POISON_NOCHECK 0x0
> +#define KMSAN_POISON_CHECK 0x1
> +#define KMSAN_POISON_FREE 0x2
> +
> +#define KMSAN_ORIGIN_SIZE 4
> +
> +#define KMSAN_STACK_DEPTH 64
> +
> +#define KMSAN_META_SHADOW (false)
> +#define KMSAN_META_ORIGIN (true)
> +
> +extern bool kmsan_enabled;
> +extern int panic_on_kmsan;
> +
> +/*
> + * KMSAN performs a lot of consistency checks that are currently enabled by
> + * default. BUG_ON is normally discouraged in the kernel, unless used for
> + * debugging, but KMSAN itself is a debugging tool, so it makes little sense to
> + * recover if something goes wrong.
> + */
> +#define KMSAN_WARN_ON(cond) \
> + ({ \
> + const bool __cond = WARN_ON(cond); \
> + if (unlikely(__cond)) { \
> + WRITE_ONCE(kmsan_enabled, false); \
> + if (panic_on_kmsan) { \
> + /* Can't call panic() here because */ \
> + /* of uaccess checks.*/ \

space after '.'

> + BUG(); \
> + } \
> + } \
> + __cond; \
> + })
> +
> +/*
> + * A pair of metadata pointers to be returned by the instrumentation functions.
> + */
> +struct shadow_origin_ptr {
> + void *shadow, *origin;
> +};
> +
> +struct shadow_origin_ptr kmsan_get_shadow_origin_ptr(void *addr, u64 size,
> + bool store);
> +void *kmsan_get_metadata(void *addr, bool is_origin);
> +
> +enum kmsan_bug_reason {
> + REASON_ANY,
> + REASON_COPY_TO_USER,
> + REASON_SUBMIT_URB,
> +};
> +
> +void kmsan_print_origin(depot_stack_handle_t origin);
> +
> +/**
> + * kmsan_report() - Report a use of uninitialized value.
> + * @origin: Stack ID of the uninitialized value.
> + * @address: Address at which the memory access happens.
> + * @size: Memory access size.
> + * @off_first: Offset (from @address) of the first byte to be reported.
> + * @off_last: Offset (from @address) of the last byte to be reported.
> + * @user_addr: When non-NULL, denotes the userspace address to which the kernel
> + * is leaking data.
> + * @reason: Error type from enum kmsan_bug_reason.
> + *
> + * kmsan_report() prints an error message for a consequent group of bytes
> + * sharing the same origin. If an uninitialized value is used in a comparison,
> + * this function is called once without specifying the addresses. When checking
> + * a memory range, KMSAN may call kmsan_report() multiple times with the same
> + * @address, @size, @user_addr and @reason, but different @off_first and
> + * @off_last corresponding to different @origin values.
> + */
> +void kmsan_report(depot_stack_handle_t origin, void *address, int size,
> + int off_first, int off_last, const void *user_addr,
> + enum kmsan_bug_reason reason);
> +
> +DECLARE_PER_CPU(struct kmsan_ctx, kmsan_percpu_ctx);
> +
> +static __always_inline struct kmsan_ctx *kmsan_get_context(void)
> +{
> + return in_task() ? &current->kmsan_ctx : raw_cpu_ptr(&kmsan_percpu_ctx);
> +}
> +
> +/*
> + * When a compiler hook is invoked, it may make a call to instrumented code
> + * and eventually call itself recursively. To avoid that, we protect the
> + * runtime entry points with kmsan_enter_runtime()/kmsan_leave_runtime() and
> + * exit the hook if kmsan_in_runtime() is true.
> + */
> +
> +static __always_inline bool kmsan_in_runtime(void)
> +{
> + if ((hardirq_count() >> HARDIRQ_SHIFT) > 1)
> + return true;
> + return kmsan_get_context()->kmsan_in_runtime;
> +}
> +
> +static __always_inline void kmsan_enter_runtime(void)
> +{
> + struct kmsan_ctx *ctx;
> +
> + ctx = kmsan_get_context();
> + KMSAN_WARN_ON(ctx->kmsan_in_runtime++);
> +}
> +
> +static __always_inline void kmsan_leave_runtime(void)
> +{
> + struct kmsan_ctx *ctx = kmsan_get_context();
> +
> + KMSAN_WARN_ON(--ctx->kmsan_in_runtime);
> +}
> +
> +depot_stack_handle_t kmsan_save_stack(void);
> +depot_stack_handle_t kmsan_save_stack_with_flags(gfp_t flags,
> + unsigned int extra_bits);
> +
> +/*
> + * Pack and unpack the origin chain depth and UAF flag to/from the extra bits
> + * provided by the stack depot.
> + * The UAF flag is stored in the lowest bit, followed by the depth in the upper
> + * bits.
> + * set_dsh_extra_bits() is responsible for clamping the value.
> + */
> +static __always_inline unsigned int kmsan_extra_bits(unsigned int depth,
> + bool uaf)
> +{
> + return (depth << 1) | uaf;
> +}
> +
> +static __always_inline bool kmsan_uaf_from_eb(unsigned int extra_bits)
> +{
> + return extra_bits & 1;
> +}
> +
> +static __always_inline unsigned int kmsan_depth_from_eb(unsigned int extra_bits)
> +{
> + return extra_bits >> 1;
> +}
> +
> +/*
> + * kmsan_internal_ functions are supposed to be very simple and not require the
> + * kmsan_in_runtime() checks.
> + */
> +void kmsan_internal_memmove_metadata(void *dst, void *src, size_t n);
> +void kmsan_internal_poison_memory(void *address, size_t size, gfp_t flags,
> + unsigned int poison_flags);
> +void kmsan_internal_unpoison_memory(void *address, size_t size, bool checked);
> +void kmsan_internal_set_shadow_origin(void *address, size_t size, int b,
> + u32 origin, bool checked);
> +depot_stack_handle_t kmsan_internal_chain_origin(depot_stack_handle_t id);
> +
> +bool kmsan_metadata_is_contiguous(void *addr, size_t size);
> +void kmsan_internal_check_memory(void *addr, size_t size, const void *user_addr,
> + int reason);
> +bool kmsan_internal_is_module_addr(void *vaddr);
> +bool kmsan_internal_is_vmalloc_addr(void *addr);
> +
> +struct page *kmsan_vmalloc_to_page_or_null(void *vaddr);
> +
> +#endif /* __MM_KMSAN_KMSAN_H */
> diff --git a/mm/kmsan/report.c b/mm/kmsan/report.c
> new file mode 100644
> index 0000000000000..f36fca452e313
> --- /dev/null
> +++ b/mm/kmsan/report.c
> @@ -0,0 +1,211 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KMSAN error reporting routines.
> + *
> + * Copyright (C) 2019-2022 Google LLC
> + * Author: Alexander Potapenko <glider@xxxxxxxxxx>
> + *
> + */
> +
> +#include <linux/console.h>
> +#include <linux/moduleparam.h>
> +#include <linux/stackdepot.h>
> +#include <linux/stacktrace.h>
> +#include <linux/uaccess.h>
> +
> +#include "kmsan.h"
> +
> +static DEFINE_SPINLOCK(kmsan_report_lock);
> +#define DESCR_SIZE 128
> +/* Protected by kmsan_report_lock */
> +static char report_local_descr[DESCR_SIZE];
> +int panic_on_kmsan __read_mostly;
> +
> +#ifdef MODULE_PARAM_PREFIX
> +#undef MODULE_PARAM_PREFIX
> +#endif
> +#define MODULE_PARAM_PREFIX "kmsan."
> +module_param_named(panic, panic_on_kmsan, int, 0);
> +
> +/*
> + * Skip internal KMSAN frames.
> + */
> +static int get_stack_skipnr(const unsigned long stack_entries[],
> + int num_entries)
> +{
> + int len, skip;
> + char buf[64];
> +
> + for (skip = 0; skip < num_entries; ++skip) {
> + len = scnprintf(buf, sizeof(buf), "%ps",
> + (void *)stack_entries[skip]);
> +
> + /* Never show __msan_* or kmsan_* functions. */
> + if ((strnstr(buf, "__msan_", len) == buf) ||
> + (strnstr(buf, "kmsan_", len) == buf))
> + continue;
> +
> + /*
> + * No match for runtime functions -- @skip entries to skip to
> + * get to first frame of interest.
> + */
> + break;
> + }
> +
> + return skip;
> +}
> +
> +/*
> + * Currently the descriptions of locals generated by Clang look as follows:
> + * ----local_name@function_name
> + * We want to print only the name of the local, as other information in that
> + * description can be confusing.
> + * The meaningful part of the description is copied to a global buffer to avoid
> + * allocating memory.
> + */
> +static char *pretty_descr(char *descr)
> +{
> + int i, pos = 0, len = strlen(descr);
> +
> + for (i = 0; i < len; i++) {
> + if (descr[i] == '@')
> + break;
> + if (descr[i] == '-')
> + continue;
> + report_local_descr[pos] = descr[i];
> + if (pos + 1 == DESCR_SIZE)
> + break;
> + pos++;
> + }
> + report_local_descr[pos] = 0;
> + return report_local_descr;
> +}
> +
> +void kmsan_print_origin(depot_stack_handle_t origin)
> +{
> + unsigned long *entries = NULL, *chained_entries = NULL;
> + unsigned int nr_entries, chained_nr_entries, skipnr;
> + void *pc1 = NULL, *pc2 = NULL;
> + depot_stack_handle_t head;
> + unsigned long magic;
> + char *descr = NULL;
> +
> + if (!origin)
> + return;
> +
> + while (true) {
> + nr_entries = stack_depot_fetch(origin, &entries);
> + magic = nr_entries ? entries[0] : 0;
> + if ((nr_entries == 4) && (magic == KMSAN_ALLOCA_MAGIC_ORIGIN)) {
> + descr = (char *)entries[1];
> + pc1 = (void *)entries[2];
> + pc2 = (void *)entries[3];
> + pr_err("Local variable %s created at:\n",
> + pretty_descr(descr));
> + if (pc1)
> + pr_err(" %pSb\n", pc1);
> + if (pc2)
> + pr_err(" %pSb\n", pc2);
> + break;
> + }
> + if ((nr_entries == 3) && (magic == KMSAN_CHAIN_MAGIC_ORIGIN)) {
> + head = entries[1];
> + origin = entries[2];
> + pr_err("Uninit was stored to memory at:\n");
> + chained_nr_entries =
> + stack_depot_fetch(head, &chained_entries);
> + kmsan_internal_unpoison_memory(
> + chained_entries,
> + chained_nr_entries * sizeof(*chained_entries),
> + /*checked*/ false);
> + skipnr = get_stack_skipnr(chained_entries,
> + chained_nr_entries);
> + stack_trace_print(chained_entries + skipnr,
> + chained_nr_entries - skipnr, 0);
> + pr_err("\n");
> + continue;
> + }
> + pr_err("Uninit was created at:\n");
> + if (nr_entries) {
> + skipnr = get_stack_skipnr(entries, nr_entries);
> + stack_trace_print(entries + skipnr, nr_entries - skipnr,
> + 0);
> + } else {
> + pr_err("(stack is not available)\n");
> + }
> + break;
> + }
> +}
> +
> +void kmsan_report(depot_stack_handle_t origin, void *address, int size,
> + int off_first, int off_last, const void *user_addr,
> + enum kmsan_bug_reason reason)
> +{
> + unsigned long stack_entries[KMSAN_STACK_DEPTH];
> + int num_stack_entries, skipnr;
> + char *bug_type = NULL;
> + unsigned long flags, ua_flags;
> + bool is_uaf;
> +
> + if (!kmsan_enabled)
> + return;
> + if (!current->kmsan_ctx.allow_reporting)
> + return;
> + if (!origin)
> + return;
> +
> + current->kmsan_ctx.allow_reporting = false;
> + ua_flags = user_access_save();
> + spin_lock_irqsave(&kmsan_report_lock, flags);

I think this might want to be a raw_spin_lock, since the reporting can
be called from any context, including from within other raw_spin_lock'd
critical sections (practically this will only matter in RT kernels).

Also, do you have to do lockdep_off/on() (like kernel/kcsan/report.c
does, see comment there)?

> + pr_err("=====================================================\n");
> + is_uaf = kmsan_uaf_from_eb(stack_depot_get_extra_bits(origin));
> + switch (reason) {
> + case REASON_ANY:
> + bug_type = is_uaf ? "use-after-free" : "uninit-value";
> + break;
> + case REASON_COPY_TO_USER:
> + bug_type = is_uaf ? "kernel-infoleak-after-free" :
> + "kernel-infoleak";
> + break;
> + case REASON_SUBMIT_URB:
> + bug_type = is_uaf ? "kernel-usb-infoleak-after-free" :
> + "kernel-usb-infoleak";
> + break;
> + }
> +
> + num_stack_entries =
> + stack_trace_save(stack_entries, KMSAN_STACK_DEPTH, 1);
> + skipnr = get_stack_skipnr(stack_entries, num_stack_entries);
> +
> + pr_err("BUG: KMSAN: %s in %pSb\n",
> + bug_type, (void *)stack_entries[skipnr]);
> + stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
> + 0);
> + pr_err("\n");
> +
> + kmsan_print_origin(origin);
> +
> + if (size) {
> + pr_err("\n");
> + if (off_first == off_last)
> + pr_err("Byte %d of %d is uninitialized\n", off_first,
> + size);
> + else
> + pr_err("Bytes %d-%d of %d are uninitialized\n",
> + off_first, off_last, size);
> + }
> + if (address)
> + pr_err("Memory access of size %d starts at %px\n", size,
> + address);
> + if (user_addr && reason == REASON_COPY_TO_USER)
> + pr_err("Data copied to user address %px\n", user_addr);
> + pr_err("\n");
> + dump_stack_print_info(KERN_ERR);
> + pr_err("=====================================================\n");
> + add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
> + spin_unlock_irqrestore(&kmsan_report_lock, flags);
> + if (panic_on_kmsan)
> + panic("kmsan.panic set ...\n");
> + user_access_restore(ua_flags);
> + current->kmsan_ctx.allow_reporting = true;
> +}
> diff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c
> new file mode 100644
> index 0000000000000..de58cfbc55b9d
> --- /dev/null
> +++ b/mm/kmsan/shadow.c
> @@ -0,0 +1,186 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KMSAN shadow implementation.
> + *
> + * Copyright (C) 2017-2022 Google LLC
> + * Author: Alexander Potapenko <glider@xxxxxxxxxx>
> + *
> + */
> +
> +#include <asm/page.h>
> +#include <asm/pgtable_64_types.h>
> +#include <asm/tlbflush.h>
> +#include <linux/cacheflush.h>
> +#include <linux/memblock.h>
> +#include <linux/mm_types.h>
> +#include <linux/percpu-defs.h>
> +#include <linux/slab.h>
> +#include <linux/smp.h>
> +#include <linux/stddef.h>
> +
> +#include "../internal.h"
> +#include "kmsan.h"
> +
> +#define shadow_page_for(page) ((page)->kmsan_shadow)
> +
> +#define origin_page_for(page) ((page)->kmsan_origin)
> +
> +static void *shadow_ptr_for(struct page *page)
> +{
> + return page_address(shadow_page_for(page));
> +}
> +
> +static void *origin_ptr_for(struct page *page)
> +{
> + return page_address(origin_page_for(page));
> +}
> +
> +static bool page_has_metadata(struct page *page)
> +{
> + return shadow_page_for(page) && origin_page_for(page);
> +}
> +
> +static void set_no_shadow_origin_page(struct page *page)
> +{
> + shadow_page_for(page) = NULL;
> + origin_page_for(page) = NULL;
> +}
> +
> +/*
> + * Dummy load and store pages to be used when the real metadata is unavailable.
> + * There are separate pages for loads and stores, so that every load returns a
> + * zero, and every store doesn't affect other loads.
> + */
> +static char dummy_load_page[PAGE_SIZE] __aligned(PAGE_SIZE);
> +static char dummy_store_page[PAGE_SIZE] __aligned(PAGE_SIZE);
> +
> +/*
> + * Taken from arch/x86/mm/physaddr.h to avoid using an instrumented version.
> + */
> +static int kmsan_phys_addr_valid(unsigned long addr)

int -> bool ? (it already deviates from the original by using IS_ENABLED
instead of #ifdef)

> +{
> + if (IS_ENABLED(CONFIG_PHYS_ADDR_T_64BIT))
> + return !(addr >> boot_cpu_data.x86_phys_bits);
> + else
> + return 1;
> +}
> +
> +/*
> + * Taken from arch/x86/mm/physaddr.c to avoid using an instrumented version.
> + */
> +static bool kmsan_virt_addr_valid(void *addr)
> +{
> + unsigned long x = (unsigned long)addr;
> + unsigned long y = x - __START_KERNEL_map;
> +
> + /* use the carry flag to determine if x was < __START_KERNEL_map */
> + if (unlikely(x > y)) {
> + x = y + phys_base;
> +
> + if (y >= KERNEL_IMAGE_SIZE)
> + return false;
> + } else {
> + x = y + (__START_KERNEL_map - PAGE_OFFSET);
> +
> + /* carry flag will be set if starting x was >= PAGE_OFFSET */
> + if ((x > y) || !kmsan_phys_addr_valid(x))
> + return false;
> + }
> +
> + return pfn_valid(x >> PAGE_SHIFT);
> +}

These seem quite x86-specific - to ease eventual porting to other
architectures, it would make sense to introduce <asm/kmsan.h> which will
have these 2 functions (and if there's anything else arch-specific like
this, moving to <asm/kmsan.h> would help eventual ports).

> +static unsigned long vmalloc_meta(void *addr, bool is_origin)
> +{
> + unsigned long addr64 = (unsigned long)addr, off;
> +
> + KMSAN_WARN_ON(is_origin && !IS_ALIGNED(addr64, KMSAN_ORIGIN_SIZE));
> + if (kmsan_internal_is_vmalloc_addr(addr)) {
> + off = addr64 - VMALLOC_START;
> + return off + (is_origin ? KMSAN_VMALLOC_ORIGIN_START :
> + KMSAN_VMALLOC_SHADOW_START);
> + }
> + if (kmsan_internal_is_module_addr(addr)) {
> + off = addr64 - MODULES_VADDR;
> + return off + (is_origin ? KMSAN_MODULES_ORIGIN_START :
> + KMSAN_MODULES_SHADOW_START);
> + }
> + return 0;
> +}
> +
> +static struct page *virt_to_page_or_null(void *vaddr)
> +{
> + if (kmsan_virt_addr_valid(vaddr))
> + return virt_to_page(vaddr);
> + else
> + return NULL;
> +}
> +
> +struct shadow_origin_ptr kmsan_get_shadow_origin_ptr(void *address, u64 size,
> + bool store)
> +{
> + struct shadow_origin_ptr ret;
> + void *shadow;
> +
> + /*
> + * Even if we redirect this memory access to the dummy page, it will
> + * go out of bounds.
> + */
> + KMSAN_WARN_ON(size > PAGE_SIZE);
> +
> + if (!kmsan_enabled || kmsan_in_runtime())
> + goto return_dummy;
> +
> + KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(address, size));
> + shadow = kmsan_get_metadata(address, KMSAN_META_SHADOW);
> + if (!shadow)
> + goto return_dummy;
> +
> + ret.shadow = shadow;
> + ret.origin = kmsan_get_metadata(address, KMSAN_META_ORIGIN);
> + return ret;
> +
> +return_dummy:
> + if (store) {
> + /* Ignore this store. */
> + ret.shadow = dummy_store_page;
> + ret.origin = dummy_store_page;
> + } else {
> + /* This load will return zero. */
> + ret.shadow = dummy_load_page;
> + ret.origin = dummy_load_page;
> + }
> + return ret;
> +}
> +
> +/*
> + * Obtain the shadow or origin pointer for the given address, or NULL if there's
> + * none. The caller must check the return value for being non-NULL if needed.
> + * The return value of this function should not depend on whether we're in the
> + * runtime or not.
> + */
> +void *kmsan_get_metadata(void *address, bool is_origin)
> +{
> + u64 addr = (u64)address, pad, off;
> + struct page *page;
> + void *ret;
> +
> + if (is_origin && !IS_ALIGNED(addr, KMSAN_ORIGIN_SIZE)) {
> + pad = addr % KMSAN_ORIGIN_SIZE;
> + addr -= pad;
> + }
> + address = (void *)addr;
> + if (kmsan_internal_is_vmalloc_addr(address) ||
> + kmsan_internal_is_module_addr(address))
> + return (void *)vmalloc_meta(address, is_origin);
> +
> + page = virt_to_page_or_null(address);
> + if (!page)
> + return NULL;
> + if (!page_has_metadata(page))
> + return NULL;
> + off = addr % PAGE_SIZE;
> +
> + ret = (is_origin ? origin_ptr_for(page) : shadow_ptr_for(page)) + off;

Just return this and avoid 'ret'?

> + return ret;
> +}
> diff --git a/scripts/Makefile.kmsan b/scripts/Makefile.kmsan
> new file mode 100644
> index 0000000000000..9793591f9855c
> --- /dev/null
> +++ b/scripts/Makefile.kmsan
> @@ -0,0 +1 @@

Makefile.kmsan needs SPDX-License-Identifier.

> +export CFLAGS_KMSAN := -fsanitize=kernel-memory
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 9f69ecdd7977a..49e6e57fdf4c8 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -157,6 +157,15 @@ _c_flags += $(if $(patsubst n%,, \
> endif
> endif
>
> +ifeq ($(CONFIG_KMSAN),y)
> +_c_flags += $(if $(patsubst n%,, \
> + $(KMSAN_SANITIZE_$(basetarget).o)$(KMSAN_SANITIZE)y), \
> + $(CFLAGS_KMSAN))
> +_c_flags += $(if $(patsubst n%,, \
> + $(KMSAN_ENABLE_CHECKS_$(basetarget).o)$(KMSAN_ENABLE_CHECKS)y), \
> + , -mllvm -msan-disable-checks=1)
> +endif
> +
> ifeq ($(CONFIG_UBSAN),y)
> _c_flags += $(if $(patsubst n%,, \
> $(UBSAN_SANITIZE_$(basetarget).o)$(UBSAN_SANITIZE)$(CONFIG_UBSAN_SANITIZE_ALL)), \
> --
> 2.36.0.rc2.479.g8af0fa9b8e-goog
>