Re: [PATCH 1/2] kasan: Fix Software Tag-Based KASAN with GCC

[Will Deacon]

On Tue, Oct 22, 2024 at 11:42:40PM +0200, Marco Elver wrote:
> On Mon, 21 Oct 2024 at 19:29, Andrew Pinski <pinskia@xxxxxxxxx> wrote:
> >
> > On Mon, Oct 21, 2024 at 10:21 AM Will Deacon <will@xxxxxxxxxx> wrote:
> > >
> > > On Mon, Oct 21, 2024 at 02:00:10PM +0200, Marco Elver wrote:
> > > > Per [1], -fsanitize=kernel-hwaddress with GCC currently does not disable
> > > > instrumentation in functions with __attribute__((no_sanitize_address)).
> > > >
> > > > However, __attribute__((no_sanitize("hwaddress"))) does correctly
> > > > disable instrumentation. Use it instead.
> > > >
> > > > Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117196 [1]
> > > > Link: https://lore.kernel.org/r/000000000000f362e80620e27859@xxxxxxxxxx
> > > > Link: https://lore.kernel.org/r/ZvFGwKfoC4yVjN_X@J2N7QTR9R3
> > > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=218854
> > > > Reported-by: syzbot+908886656a02769af987@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > > Tested-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> > > > Cc: Andrew Pinski <pinskia@xxxxxxxxx>
> > > > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > > > Cc: Will Deacon <will@xxxxxxxxxx>
> > > > Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> > > > ---
> > > >  include/linux/compiler-gcc.h | 4 ++++
> > > >  1 file changed, 4 insertions(+)
> > > >
> > > > diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> > > > index f805adaa316e..cd6f9aae311f 100644
> > > > --- a/include/linux/compiler-gcc.h
> > > > +++ b/include/linux/compiler-gcc.h
> > > > @@ -80,7 +80,11 @@
> > > >  #define __noscs __attribute__((__no_sanitize__("shadow-call-stack")))
> > > >  #endif
> > > >
> > > > +#ifdef __SANITIZE_HWADDRESS__
> > > > +#define __no_sanitize_address __attribute__((__no_sanitize__("hwaddress")))
> > > > +#else
> > > >  #define __no_sanitize_address __attribute__((__no_sanitize_address__))
> > > > +#endif
> > >
> > > Does this work correctly for all versions of GCC that support
> > > -fsanitize=kernel-hwaddress?
> >
> > Yes, tested from GCC 11+, kernel-hwaddress was added in GCC 11.
> > Also tested from clang 9.0+ and it works there too.
> 
> +1 yes. From what I can tell GCC always supported
> no_sanitize("hwaddress") for -fsanitize=kernel-hwaddress.

Thanks, both, for confirming this. I'll pick these up as fixes in the
arm64 tree.

> Even for Clang, we define __no_sanitize_address to include
> no_sanitize("hwaddress"):
> https://elixir.bootlin.com/linux/v6.11.4/source/include/linux/compiler-clang.h#L29
> 
> So this has just been an oversight when GCC support for KASAN_SW_TAGS
> was introduced.
> 
> Having a Fixes tag for this would be nice, but I don't think we
> explicitly added GCC support, and instead just relied on
> CC_HAS_KASAN_SW_TAGS with cc-option telling us if the flag is
> supported.
> 
> But maybe we can use this:
> 
> Fixes: 7b861a53e46b ("kasan: Bump required compiler version")

I can add that to patch 1.

Will