Re: [PATCH 1/8] kasan,x86: Frob kasan_report() in an exception

From: Dmitry Vyukov
Date: Thu Feb 28 2019 - 10:22:25 EST

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On Thu, Feb 28, 2019 at 4:05 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> Because __asan_{load,store}{N,1,2,4,8,16}_noabort() get called from
> UACCESS context, and kasan_report() is most definitely _NOT_ safe to
> be called from there, move it into an exception much like BUG/WARN.
>
> *compile tested only*

Please test it by booting KASAN kernel and then loading module
produced by CONFIG_TEST_KASAN=y. There are too many subtle aspects to
rely on "compile tested only", reviewers can't catch all of them
either.

> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
> arch/x86/include/asm/bug.h | 28 ++++++++++++++--------------
> arch/x86/include/asm/kasan.h | 15 +++++++++++++++
> include/asm-generic/bug.h | 1 +
> include/linux/kasan.h | 12 +++++++++---
> lib/bug.c | 9 ++++++++-
> mm/kasan/generic.c | 4 ++--
> mm/kasan/kasan.h | 2 +-
> mm/kasan/report.c | 2 +-
> 8 files changed, 51 insertions(+), 22 deletions(-)
>
> --- a/arch/x86/include/asm/bug.h
> +++ b/arch/x86/include/asm/bug.h
> @@ -30,33 +30,33 @@
>
> #ifdef CONFIG_DEBUG_BUGVERBOSE
>
> -#define _BUG_FLAGS(ins, flags) \
> +#define _BUG_FLAGS(ins, flags, ...) \
> do { \
> asm volatile("1:\t" ins "\n" \
> ".pushsection __bug_table,\"aw\"\n" \
> - "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
> - "\t" __BUG_REL(%c0) "\t# bug_entry::file\n" \
> - "\t.word %c1" "\t# bug_entry::line\n" \
> - "\t.word %c2" "\t# bug_entry::flags\n" \
> - "\t.org 2b+%c3\n" \
> + "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
> + "\t" __BUG_REL(%c[file]) "\t# bug_entry::file\n" \
> + "\t.word %c[line]" "\t# bug_entry::line\n" \
> + "\t.word %c[flag]" "\t# bug_entry::flags\n" \
> + "\t.org 2b+%c[size]\n" \
> ".popsection" \
> - : : "i" (__FILE__), "i" (__LINE__), \
> - "i" (flags), \
> - "i" (sizeof(struct bug_entry))); \
> + : : [file] "i" (__FILE__), [line] "i" (__LINE__), \
> + [flag] "i" (flags), \
> + [size] "i" (sizeof(struct bug_entry)), ##__VA_ARGS__); \
> } while (0)
>
> #else /* !CONFIG_DEBUG_BUGVERBOSE */
>
> -#define _BUG_FLAGS(ins, flags) \
> +#define _BUG_FLAGS(ins, flags, ...) \
> do { \
> asm volatile("1:\t" ins "\n" \
> ".pushsection __bug_table,\"aw\"\n" \
> "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
> - "\t.word %c0" "\t# bug_entry::flags\n" \
> - "\t.org 2b+%c1\n" \
> + "\t.word %c[flag]" "\t# bug_entry::flags\n" \
> + "\t.org 2b+%c[size]\n" \
> ".popsection" \
> - : : "i" (flags), \
> - "i" (sizeof(struct bug_entry))); \
> + : : [flag] "i" (flags), \
> + [size] "i" (sizeof(struct bug_entry)), ##__VA_ARGS__); \
> } while (0)
>
> #endif /* CONFIG_DEBUG_BUGVERBOSE */
> --- a/arch/x86/include/asm/kasan.h
> +++ b/arch/x86/include/asm/kasan.h
> @@ -2,6 +2,8 @@
> #ifndef _ASM_X86_KASAN_H
> #define _ASM_X86_KASAN_H
>
> +#include <asm/bug.h>
> +
> #include <linux/const.h>
> #define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
> #define KASAN_SHADOW_SCALE_SHIFT 3
> @@ -26,8 +28,21 @@
> #ifndef __ASSEMBLY__
>
> #ifdef CONFIG_KASAN
> +
> void __init kasan_early_init(void);
> void __init kasan_init(void);
> +
> +static __always_inline void
> +kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
> +{
> + unsigned long rdi = addr, rsi = size, rdx = is_write, rcx = ip;
> +
> + _BUG_FLAGS(ASM_UD2, BUGFLAG_KASAN,
> + "D" (rdi), "S" (rsi), "d" (rdx), "c" (rcx));

Can BUG return? This should be able to return.
We also have other tools coming (KMSAN/KTSAN) where distinction
between fast path that does nothing and slower-paths are very blurred
and there are dozens of them, I don't think this BUG thunk will be
sustainable. What does BUG do what a normal call can't do?

> + annotate_reachable();
> +}
> +#define kasan_report kasan_report
> +
> #else
> static inline void kasan_early_init(void) { }
> static inline void kasan_init(void) { }
> --- a/include/asm-generic/bug.h
> +++ b/include/asm-generic/bug.h
> @@ -10,6 +10,7 @@
> #define BUGFLAG_WARNING (1 << 0)
> #define BUGFLAG_ONCE (1 << 1)
> #define BUGFLAG_DONE (1 << 2)
> +#define BUGFLAG_KASAN (1 << 3)
> #define BUGFLAG_TAINT(taint) ((taint) << 8)
> #define BUG_GET_TAINT(bug) ((bug)->flags >> 8)
> #endif
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -83,6 +83,9 @@ size_t kasan_metadata_size(struct kmem_c
> bool kasan_save_enable_multi_shot(void);
> void kasan_restore_multi_shot(bool enabled);
>
> +void __kasan_report(unsigned long addr, size_t size,
> + bool is_write, unsigned long ip);
> +
> #else /* CONFIG_KASAN */
>
> static inline void kasan_unpoison_shadow(const void *address, size_t size) {}
> @@ -153,8 +156,14 @@ static inline void kasan_remove_zero_sha
> static inline void kasan_unpoison_slab(const void *ptr) { }
> static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
>
> +static inline void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip) { }
> +
> #endif /* CONFIG_KASAN */
>
> +#ifndef kasan_report
> +#define kasan_report(addr, size, is_write, ip) __kasan_report(addr, size, is_write, ip)
> +#endif
> +
> #ifdef CONFIG_KASAN_GENERIC
>
> #define KASAN_SHADOW_INIT 0
> @@ -177,9 +186,6 @@ void kasan_init_tags(void);
>
> void *kasan_reset_tag(const void *addr);
>
> -void kasan_report(unsigned long addr, size_t size,
> - bool is_write, unsigned long ip);
> -
> #else /* CONFIG_KASAN_SW_TAGS */
>
> static inline void kasan_init_tags(void) { }
> --- a/lib/bug.c
> +++ b/lib/bug.c
> @@ -47,6 +47,7 @@
> #include <linux/bug.h>
> #include <linux/sched.h>
> #include <linux/rculist.h>
> +#include <linux/kasan.h>
>
> extern struct bug_entry __start___bug_table[], __stop___bug_table[];
>
> @@ -144,7 +145,7 @@ enum bug_trap_type report_bug(unsigned l
> {
> struct bug_entry *bug;
> const char *file;
> - unsigned line, warning, once, done;
> + unsigned line, warning, once, done, kasan;
>
> if (!is_valid_bugaddr(bugaddr))
> return BUG_TRAP_TYPE_NONE;
> @@ -167,6 +168,7 @@ enum bug_trap_type report_bug(unsigned l
> line = bug->line;
> #endif
> warning = (bug->flags & BUGFLAG_WARNING) != 0;
> + kasan = (bug->flags & BUGFLAG_KASAN) != 0;
> once = (bug->flags & BUGFLAG_ONCE) != 0;
> done = (bug->flags & BUGFLAG_DONE) != 0;
>
> @@ -188,6 +190,11 @@ enum bug_trap_type report_bug(unsigned l
> return BUG_TRAP_TYPE_WARN;
> }
>
> + if (kasan) {
> + __kasan_report(regs->di, regs->si, regs->dx, regs->cx);
> + return BUG_TRAP_TYPE_WARN;
> + }
> +
> printk(KERN_DEFAULT CUT_HERE);
>
> if (file)
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -228,7 +228,7 @@ void __asan_unregister_globals(struct ka
> EXPORT_SYMBOL(__asan_unregister_globals);
>
> #define DEFINE_ASAN_LOAD_STORE(size) \
> - void __asan_load##size(unsigned long addr) \
> + notrace void __asan_load##size(unsigned long addr) \

We already have:
CFLAGS_REMOVE_generic.o = -pg
Doesn't it imply notrace for all functions?

> { \
> check_memory_region_inline(addr, size, false, _RET_IP_);\
> } \
> @@ -236,7 +236,7 @@ EXPORT_SYMBOL(__asan_unregister_globals)
> __alias(__asan_load##size) \
> void __asan_load##size##_noabort(unsigned long); \
> EXPORT_SYMBOL(__asan_load##size##_noabort); \
> - void __asan_store##size(unsigned long addr) \
> + notrace void __asan_store##size(unsigned long addr) \
> { \
> check_memory_region_inline(addr, size, true, _RET_IP_); \
> } \
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -130,7 +130,7 @@ void check_memory_region(unsigned long a
> void *find_first_bad_addr(void *addr, size_t size);
> const char *get_bug_type(struct kasan_access_info *info);
>
> -void kasan_report(unsigned long addr, size_t size,
> +void __kasan_report(unsigned long addr, size_t size,
> bool is_write, unsigned long ip);
> void kasan_report_invalid_free(void *object, unsigned long ip);
>
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -281,7 +281,7 @@ void kasan_report_invalid_free(void *obj
> end_report(&flags);
> }
>
> -void kasan_report(unsigned long addr, size_t size,
> +void __kasan_report(unsigned long addr, size_t size,
> bool is_write, unsigned long ip)
> {
> struct kasan_access_info info;
>
>

Next message: Måns Rullgård: "Re: [RFC][PATCH] dt-bindings: usb: add non-removable device property"
Previous message: Sasha Levin: "[PATCH AUTOSEL 4.14 02/36] arm64: dts: renesas: r8a7796: Enable DMA for SCIF2"
In reply to: Peter Zijlstra: "[PATCH 1/8] kasan,x86: Frob kasan_report() in an exception"
Next in thread: Peter Zijlstra: "Re: [PATCH 1/8] kasan,x86: Frob kasan_report() in an exception"
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