Re: [PATCH] kasan: prevent recursive instrumentation

[Mark Rutland]

On Sat, Feb 23, 2019 at 11:29:45AM +0100, Dmitry Vyukov wrote:
> 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

I had missed that patch -- thanks for the pointer!

Either patch should both fix the issue with the EFI stub, but the
__kasan_check*() renaming in this patch also prevents unexpected
instrumentation within mm/kasan/common.c, if a call to kasan_check_*()
were inlined there.

If you think that robustness is worthwhile, I can spin a v2 making that
a bit clearer, and fix the logic to look at __SANITIZE_ADDRESS__ rather
than adding the KASAN_NOSANITIZE definition.

AFAICT Arnd's patch isn't queued anywhere just yet.

Thanks,
Mark.

> > 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
> >