Re: [PATCH] kasan: prevent recursive instrumentation

[Dmitry Vyukov]

On Fri, Feb 22, 2019 at 7:29 PM Mark Rutland <mark.rutland@xxxxxxx> wrote:
>
> When CONFIG_KASAN is selected, <linux/kasan-checks.h> defines the
> prototypes for kasan_check_{read,write}(), rather than inline stubs.


+kasan-dev@xxxxxxxxxxxxxxxx

Doesn't this do the same as?
https://groups.google.com/d/msg/kasan-dev/NwEdpGgUeac/oXUIRUC6CAAJ



> This is the case even when it is included by files which are not
> instrumented by KASAN. Where helpers (e.g. the atomics) are instrumented
> with explicit calls to kasan_check_{read,write}(), this results in files
> being unexpectedly instrumented.
>
> This is problematic as it can result in instrumentation in files which
> cannot safely call these functions, such as within the EFI stub:
>
> [mark@lakrids:~/src/linux]% usekorg 8.1.0 make ARCH=arm64 CROSS_COMPILE=aarch64-linux- -j64 -s
> drivers/firmware/efi/libstub/arm-stub.stub.o: In function `atomic_set':
> /home/mark/src/linux/./include/asm-generic/atomic-instrumented.h:44: undefined reference to `__efistub_kasan_check_write'
> /home/mark/src/linux/./include/asm-generic/atomic-instrumented.h:44:(.init.text+0xa0): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `__efistub_kasan_check_write'
> Makefile:1021: recipe for target 'vmlinux' failed
> make: *** [vmlinux] Error 1
>
> Let's avoid this by ensuring that uninstrumented files are given the
> same stub definition of these functions used for !KASAN builds. So that
> the stub defintions don't conflict with the real definitions in
> (uninstrumented) common KASAN code, the real definitions are prefixed
> with underscores, and called from unprefixed macros.
>
> Any compiler-generated instrumentation uses separate
> __asan_{load,store}_*() entry points, and is not affected by this
> change.
>
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> ---
>  include/linux/kasan-checks.h | 8 +++++---
>  mm/kasan/common.c            | 8 ++++----
>  scripts/Makefile.kasan       | 2 +-
>  3 files changed, 10 insertions(+), 8 deletions(-)
>
> Hi,
>
> Assuming the KASAN folk are happy with this, I'd like this to be queued in the
> tip tree, where the arm64 instrumented atomics are already queued.
>
> Thanks,
> Mark.
>
> diff --git a/include/linux/kasan-checks.h b/include/linux/kasan-checks.h
> index d314150658a4..6cf4b41a5393 100644
> --- a/include/linux/kasan-checks.h
> +++ b/include/linux/kasan-checks.h
> @@ -2,9 +2,11 @@
>  #ifndef _LINUX_KASAN_CHECKS_H
>  #define _LINUX_KASAN_CHECKS_H
>
> -#ifdef CONFIG_KASAN
> -void kasan_check_read(const volatile void *p, unsigned int size);
> -void kasan_check_write(const volatile void *p, unsigned int size);
> +#if defined(CONFIG_KASAN) && !defined (KASAN_NOSANITIZE)
> +void __kasan_check_read(const volatile void *p, unsigned int size);
> +#define kasan_check_read __kasan_check_read
> +void __kasan_check_write(const volatile void *p, unsigned int size);
> +#define kasan_check_write __kasan_check_write
>  #else
>  static inline void kasan_check_read(const volatile void *p, unsigned int size)
>  { }
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 73c9cbfdedf4..630e32838adb 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -95,17 +95,17 @@ void kasan_disable_current(void)
>         current->kasan_depth--;
>  }
>
> -void kasan_check_read(const volatile void *p, unsigned int size)
> +void __kasan_check_read(const volatile void *p, unsigned int size)
>  {
>         check_memory_region((unsigned long)p, size, false, _RET_IP_);
>  }
> -EXPORT_SYMBOL(kasan_check_read);
> +EXPORT_SYMBOL(__kasan_check_read);
>
> -void kasan_check_write(const volatile void *p, unsigned int size)
> +void __kasan_check_write(const volatile void *p, unsigned int size)
>  {
>         check_memory_region((unsigned long)p, size, true, _RET_IP_);
>  }
> -EXPORT_SYMBOL(kasan_check_write);
> +EXPORT_SYMBOL(__kasan_check_write);
>
>  #undef memset
>  void *memset(void *addr, int c, size_t len)
> diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
> index 25c259df8ffa..c475a8ac776c 100644
> --- a/scripts/Makefile.kasan
> +++ b/scripts/Makefile.kasan
> @@ -52,5 +52,5 @@ CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
>  endif # CONFIG_KASAN_SW_TAGS
>
>  ifdef CONFIG_KASAN
> -CFLAGS_KASAN_NOSANITIZE := -fno-builtin
> +CFLAGS_KASAN_NOSANITIZE := -fno-builtin -DKASAN_NOSANITIZE
>  endif
> --
> 2.11.0
>