Re: [PATCH RFC v2 14/21] kasan: add and integrate kasan boot parameters

From: Dmitry Vyukov
Date: Wed Oct 28 2020 - 19:15:08 EST

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On Thu, Oct 22, 2020 at 3:19 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>
> TODO: no meaningful description here yet, please see the cover letter
> for this RFC series.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Link: https://linux-review.googlesource.com/id/If7d37003875b2ed3e0935702c8015c223d6416a4
> ---
> mm/kasan/common.c | 92 +++++++++++++-----------
> mm/kasan/generic.c | 5 ++
> mm/kasan/hw_tags.c | 169 ++++++++++++++++++++++++++++++++++++++++++++-
> mm/kasan/kasan.h | 9 +++
> mm/kasan/report.c | 14 +++-
> mm/kasan/sw_tags.c | 5 ++
> 6 files changed, 250 insertions(+), 44 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 1a5e6c279a72..cc129ef62ab1 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -129,35 +129,37 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
> unsigned int redzone_size;
> int redzone_adjust;
>
> - /* Add alloc meta. */
> - cache->kasan_info.alloc_meta_offset = *size;
> - *size += sizeof(struct kasan_alloc_meta);
> -
> - /* Add free meta. */
> - if (IS_ENABLED(CONFIG_KASAN_GENERIC) &&
> - (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
> - cache->object_size < sizeof(struct kasan_free_meta))) {
> - cache->kasan_info.free_meta_offset = *size;
> - *size += sizeof(struct kasan_free_meta);
> - }
> -
> - redzone_size = optimal_redzone(cache->object_size);
> - redzone_adjust = redzone_size - (*size - cache->object_size);
> - if (redzone_adjust > 0)
> - *size += redzone_adjust;
> -
> - *size = min_t(unsigned int, KMALLOC_MAX_SIZE,
> - max(*size, cache->object_size + redzone_size));
> + if (static_branch_unlikely(&kasan_stack)) {

Initially I thought kasan_stack is related to stack instrumentation.
And then wondered why we check it during slab creation.
I suggest giving it a slightly longer and more descriptive name.

... reading code further, it also disables quarantine, right?
Something to mention somewhere.

> + /* Add alloc meta. */
> + cache->kasan_info.alloc_meta_offset = *size;
> + *size += sizeof(struct kasan_alloc_meta);
> +
> + /* Add free meta. */
> + if (IS_ENABLED(CONFIG_KASAN_GENERIC) &&
> + (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
> + cache->object_size < sizeof(struct kasan_free_meta))) {
> + cache->kasan_info.free_meta_offset = *size;
> + *size += sizeof(struct kasan_free_meta);
> + }
>
> - /*
> - * If the metadata doesn't fit, don't enable KASAN at all.
> - */
> - if (*size <= cache->kasan_info.alloc_meta_offset ||
> - *size <= cache->kasan_info.free_meta_offset) {
> - cache->kasan_info.alloc_meta_offset = 0;
> - cache->kasan_info.free_meta_offset = 0;
> - *size = orig_size;
> - return;
> + redzone_size = optimal_redzone(cache->object_size);
> + redzone_adjust = redzone_size - (*size - cache->object_size);
> + if (redzone_adjust > 0)
> + *size += redzone_adjust;
> +
> + *size = min_t(unsigned int, KMALLOC_MAX_SIZE,
> + max(*size, cache->object_size + redzone_size));
> +
> + /*
> + * If the metadata doesn't fit, don't enable KASAN at all.
> + */
> + if (*size <= cache->kasan_info.alloc_meta_offset ||
> + *size <= cache->kasan_info.free_meta_offset) {
> + cache->kasan_info.alloc_meta_offset = 0;
> + cache->kasan_info.free_meta_offset = 0;
> + *size = orig_size;
> + return;
> + }
> }
>
> *flags |= SLAB_KASAN;
> @@ -165,10 +167,12 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
>
> size_t kasan_metadata_size(struct kmem_cache *cache)
> {
> - return (cache->kasan_info.alloc_meta_offset ?
> - sizeof(struct kasan_alloc_meta) : 0) +
> - (cache->kasan_info.free_meta_offset ?
> - sizeof(struct kasan_free_meta) : 0);
> + if (static_branch_unlikely(&kasan_stack))
> + return (cache->kasan_info.alloc_meta_offset ?
> + sizeof(struct kasan_alloc_meta) : 0) +
> + (cache->kasan_info.free_meta_offset ?
> + sizeof(struct kasan_free_meta) : 0);
> + return 0;
> }
>
> struct kasan_alloc_meta *kasan_get_alloc_meta(struct kmem_cache *cache,
> @@ -270,8 +274,10 @@ void * __must_check kasan_init_slab_obj(struct kmem_cache *cache,
> if (!(cache->flags & SLAB_KASAN))
> return (void *)object;
>
> - alloc_meta = kasan_get_alloc_meta(cache, object);
> - __memset(alloc_meta, 0, sizeof(*alloc_meta));
> + if (static_branch_unlikely(&kasan_stack)) {

Interestingly, now SLAB_KASAN is always set when kasan_stack is not
enabled. So it seems to me we can move the SLAB_KASAN check into this
unlikely branch now.

> + alloc_meta = kasan_get_alloc_meta(cache, object);
> + __memset(alloc_meta, 0, sizeof(*alloc_meta));
> + }
>
> if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) || IS_ENABLED(CONFIG_KASAN_HW_TAGS))
> object = set_tag(object, assign_tag(cache, object, true, false));
> @@ -308,15 +314,19 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
> rounded_up_size = round_up(cache->object_size, KASAN_GRANULE_SIZE);
> kasan_poison_memory(object, rounded_up_size, KASAN_KMALLOC_FREE);
>
> - if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) ||
> - unlikely(!(cache->flags & SLAB_KASAN)))
> - return false;
> + if (static_branch_unlikely(&kasan_stack)) {
> + if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) ||
> + unlikely(!(cache->flags & SLAB_KASAN)))
> + return false;
> +
> + kasan_set_free_info(cache, object, tag);
>
> - kasan_set_free_info(cache, object, tag);
> + quarantine_put(cache, object);
>
> - quarantine_put(cache, object);
> + return IS_ENABLED(CONFIG_KASAN_GENERIC);
> + }
>
> - return IS_ENABLED(CONFIG_KASAN_GENERIC);
> + return false;
> }
>
> bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
> @@ -355,7 +365,7 @@ static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object,
> kasan_poison_memory((void *)redzone_start, redzone_end - redzone_start,
> KASAN_KMALLOC_REDZONE);
>
> - if (cache->flags & SLAB_KASAN)
> + if (static_branch_unlikely(&kasan_stack) && (cache->flags & SLAB_KASAN))
> set_alloc_info(cache, (void *)object, flags);
>
> return set_tag(object, tag);
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index d259e4c3aefd..20a1e753e0c5 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -33,6 +33,11 @@
> #include "kasan.h"
> #include "../slab.h"
>
> +/* See the comments in hw_tags.c */
> +DEFINE_STATIC_KEY_TRUE_RO(kasan_enabled);
> +EXPORT_SYMBOL(kasan_enabled);
> +DEFINE_STATIC_KEY_TRUE_RO(kasan_stack);
> +
> /*
> * All functions below always inlined so compiler could
> * perform better optimizations in each of __asan_loadX/__assn_storeX
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index 915142da6b57..bccd781011ad 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -8,6 +8,8 @@
>
> #define pr_fmt(fmt) "kasan: " fmt
>
> +#include <linux/init.h>
> +#include <linux/jump_label.h>
> #include <linux/kasan.h>
> #include <linux/kernel.h>
> #include <linux/memory.h>
> @@ -17,10 +19,175 @@
>
> #include "kasan.h"
>
> +enum kasan_arg_mode {
> + KASAN_ARG_MODE_OFF,
> + KASAN_ARG_MODE_PROD,
> + KASAN_ARG_MODE_FULL,
> +};
> +
> +enum kasan_arg_stack {
> + KASAN_ARG_STACK_DEFAULT,
> + KASAN_ARG_STACK_OFF,
> + KASAN_ARG_STACK_ON,
> +};
> +
> +enum kasan_arg_trap {
> + KASAN_ARG_TRAP_DEFAULT,
> + KASAN_ARG_TRAP_ASYNC,
> + KASAN_ARG_TRAP_SYNC,
> +};
> +
> +enum kasan_arg_fault {
> + KASAN_ARG_FAULT_DEFAULT,
> + KASAN_ARG_FAULT_REPORT,
> + KASAN_ARG_FAULT_PANIC,
> +};
> +
> +static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
> +static enum kasan_arg_stack kasan_arg_stack __ro_after_init;
> +static enum kasan_arg_fault kasan_arg_fault __ro_after_init;
> +static enum kasan_arg_trap kasan_arg_trap __ro_after_init;
> +
> +/* Whether KASAN is enabled at all. */
> +DEFINE_STATIC_KEY_FALSE_RO(kasan_enabled);
> +EXPORT_SYMBOL(kasan_enabled);
> +
> +/* Whether to collect alloc/free stack traces. */
> +DEFINE_STATIC_KEY_FALSE_RO(kasan_stack);
> +
> +/* Whether to use synchronous or asynchronous tag checking. */
> +static bool kasan_sync __ro_after_init;
> +
> +/* Whether panic or disable tag checking on fault. */
> +bool kasan_panic __ro_after_init;
> +
> +/* kasan.mode=off/prod/full */
> +static int __init early_kasan_mode(char *arg)
> +{
> + if (!arg)
> + return -EINVAL;
> +
> + if (!strcmp(arg, "off"))
> + kasan_arg_mode = KASAN_ARG_MODE_OFF;
> + else if (!strcmp(arg, "prod"))
> + kasan_arg_mode = KASAN_ARG_MODE_PROD;
> + else if (!strcmp(arg, "full"))
> + kasan_arg_mode = KASAN_ARG_MODE_FULL;
> + else
> + return -EINVAL;
> +
> + return 0;
> +}
> +early_param("kasan.mode", early_kasan_mode);
> +
> +/* kasan.stack=off/on */
> +static int __init early_kasan_stack(char *arg)
> +{
> + if (!arg)
> + return -EINVAL;
> +
> + if (!strcmp(arg, "off"))
> + kasan_arg_stack = KASAN_ARG_STACK_OFF;
> + else if (!strcmp(arg, "on"))
> + kasan_arg_stack = KASAN_ARG_STACK_ON;
> + else
> + return -EINVAL;
> +
> + return 0;
> +}
> +early_param("kasan.stack", early_kasan_stack);
> +
> +/* kasan.trap=sync/async */
> +static int __init early_kasan_trap(char *arg)
> +{
> + if (!arg)
> + return -EINVAL;
> +
> + if (!strcmp(arg, "ASYNC"))
> + kasan_arg_trap = KASAN_ARG_TRAP_ASYNC;
> + else if (!strcmp(arg, "sync"))
> + kasan_arg_trap = KASAN_ARG_TRAP_SYNC;
> + else
> + return -EINVAL;
> +
> + return 0;
> +}
> +early_param("kasan.trap", early_kasan_trap);
> +
> +/* kasan.fault=report/panic */
> +static int __init early_kasan_fault(char *arg)
> +{
> + if (!arg)
> + return -EINVAL;
> +
> + if (!strcmp(arg, "report"))
> + kasan_arg_fault = KASAN_ARG_FAULT_REPORT;
> + else if (!strcmp(arg, "panic"))
> + kasan_arg_fault = KASAN_ARG_FAULT_PANIC;
> + else
> + return -EINVAL;
> +
> + return 0;
> +}
> +early_param("kasan.fault", early_kasan_fault);
> +
> void __init kasan_init_tags(void)
> {
> - init_tags(KASAN_TAG_MAX);
> + if (!cpu_supports_tags())
> + return;
> +
> + /* First, preset values based on the mode. */
> +
> + switch (kasan_arg_mode) {
> + case KASAN_ARG_MODE_OFF:
> + return;
> + case KASAN_ARG_MODE_PROD:
> + static_branch_enable(&kasan_enabled);
> + break;
> + case KASAN_ARG_MODE_FULL:
> + static_branch_enable(&kasan_enabled);
> + static_branch_enable(&kasan_stack);
> + kasan_sync = true;
> + break;
> + }
> +
> + /* Now, optionally override the presets. */
>
> + switch (kasan_arg_stack) {
> + case KASAN_ARG_STACK_OFF:
> + static_branch_disable(&kasan_stack);
> + break;
> + case KASAN_ARG_STACK_ON:
> + static_branch_enable(&kasan_stack);
> + break;
> + default:
> + break;
> + }
> +
> + switch (kasan_arg_trap) {
> + case KASAN_ARG_TRAP_ASYNC:
> + kasan_sync = false;
> + break;
> + case KASAN_ARG_TRAP_SYNC:
> + kasan_sync = true;
> + break;
> + default:
> + break;
> + }
> +
> + switch (kasan_arg_fault) {
> + case KASAN_ARG_FAULT_REPORT:
> + kasan_panic = false;
> + break;
> + case KASAN_ARG_FAULT_PANIC:
> + kasan_panic = true;
> + break;
> + default:
> + break;
> + }
> +
> + /* TODO: choose between sync and async based on kasan_sync. */
> + init_tags(KASAN_TAG_MAX);
> pr_info("KernelAddressSanitizer initialized\n");
> }
>
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index f7ae0c23f023..00b47bc753aa 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -2,9 +2,18 @@
> #ifndef __MM_KASAN_KASAN_H
> #define __MM_KASAN_KASAN_H
>
> +#include <linux/jump_label.h>
> #include <linux/kasan.h>
> #include <linux/stackdepot.h>
>
> +#ifdef CONFIG_KASAN_HW_TAGS
> +DECLARE_STATIC_KEY_FALSE(kasan_stack);
> +#else
> +DECLARE_STATIC_KEY_TRUE(kasan_stack);
> +#endif

kasan_stack and kasan_enabled make sense and changed only in hw_tags mode.
It would be cleaner (and faster for other modes) to abstract static keys as:

#ifdef CONFIG_KASAN_HW_TAGS
#include <linux/jump_label.h>
DECLARE_STATIC_KEY_FALSE(kasan_stack);
static inline bool kasan_stack_collection_enabled()
{
return static_branch_unlikely(&kasan_stack);
}
#else
static inline bool kasan_stack_collection_enabled() { return true; }
#endif

This way we don't need to include and define static keys for other modes.

> +extern bool kasan_panic __ro_after_init;
> +
> #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
> #define KASAN_GRANULE_SIZE (1UL << KASAN_SHADOW_SCALE_SHIFT)
> #else
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index dee5350b459c..426dd1962d3c 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -97,6 +97,10 @@ static void end_report(unsigned long *flags)
> panic_on_warn = 0;
> panic("panic_on_warn set ...\n");
> }
> +#ifdef CONFIG_KASAN_HW_TAGS
> + if (kasan_panic)
> + panic("kasan.fault=panic set ...\n");
> +#endif
> kasan_enable_current();
> }
>
> @@ -159,8 +163,8 @@ static void describe_object_addr(struct kmem_cache *cache, void *object,
> (void *)(object_addr + cache->object_size));
> }
>
> -static void describe_object(struct kmem_cache *cache, void *object,
> - const void *addr, u8 tag)
> +static void describe_object_stacks(struct kmem_cache *cache, void *object,
> + const void *addr, u8 tag)
> {
> struct kasan_alloc_meta *alloc_meta = kasan_get_alloc_meta(cache, object);
>
> @@ -188,7 +192,13 @@ static void describe_object(struct kmem_cache *cache, void *object,
> }
> #endif
> }
> +}
>
> +static void describe_object(struct kmem_cache *cache, void *object,
> + const void *addr, u8 tag)
> +{
> + if (static_branch_unlikely(&kasan_stack))
> + describe_object_stacks(cache, object, addr, tag);
> describe_object_addr(cache, object, addr);
> }
>
> diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
> index 4db41f274702..b6d185adf2c5 100644
> --- a/mm/kasan/sw_tags.c
> +++ b/mm/kasan/sw_tags.c
> @@ -33,6 +33,11 @@
> #include "kasan.h"
> #include "../slab.h"
>
> +/* See the comments in hw_tags.c */
> +DEFINE_STATIC_KEY_TRUE_RO(kasan_enabled);
> +EXPORT_SYMBOL(kasan_enabled);
> +DEFINE_STATIC_KEY_TRUE_RO(kasan_stack);
> +
> static DEFINE_PER_CPU(u32, prng_state);
>
> void __init kasan_init_tags(void)
> --
> 2.29.0.rc1.297.gfa9743e501-goog
>

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Next in thread: Andrey Konovalov: "Re: [PATCH RFC v2 14/21] kasan: add and integrate kasan boot parameters"
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