linux-kernel - Re: [PATCH] kasan: Disable Software Tag-Based KASAN with GCC

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Message-ID: <CANpmjNP5Sny0Xj0JeHU8SFFsNvgnQQ7-c3PGDmiH9RVnUF5YTA@mail.gmail.com>
Date: Fri, 18 Oct 2024 22:30:57 +0200
From: Marco Elver <elver@...gle.com>
To: Andrey Konovalov <andreyknvl@...il.com>
Cc: Will Deacon <will@...nel.org>, linux-arm-kernel@...ts.infradead.org, 
	catalin.marinas@....com, kernel-team@...roid.com, 
	linux-kernel@...r.kernel.org, ryabinin.a.a@...il.com, glider@...gle.com, 
	kasan-dev@...glegroups.com, Mark Rutland <mark.rutland@....com>, 
	syzbot+908886656a02769af987@...kaller.appspotmail.com, 
	Andrew Pinski <pinskia@...il.com>
Subject: Re: [PATCH] kasan: Disable Software Tag-Based KASAN with GCC

On Fri, 18 Oct 2024 at 22:25, Andrey Konovalov <andreyknvl@...il.com> wrote:
>
> On Fri, Oct 18, 2024 at 10:37 AM Marco Elver <elver@...gle.com> wrote:
> >
> > > Applied to arm64 (for-next/fixes), thanks!
> > >
> > > [1/1] kasan: Disable Software Tag-Based KASAN with GCC
> > >       https://git.kernel.org/arm64/c/7aed6a2c51ff
> >
> > I do not think this is the right fix. Please see alternative below.
> > Please do double-check that the observed splat above is fixed with that.
> >
> > Thanks,
> > -- Marco
> >
> > ------ >8 ------
> >
> > From 23bd83dbff5a9778f34831ed292d5e52b4b0ee18 Mon Sep 17 00:00:00 2001
> > From: Marco Elver <elver@...gle.com>
> > Date: Fri, 18 Oct 2024 10:18:24 +0200
> > Subject: [PATCH] kasan: Fix Software Tag-Based KASAN with GCC
> >
> > 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@google.com
> > Link: https://lore.kernel.org/r/ZvFGwKfoC4yVjN_X@J2N7QTR9R3
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=218854
> > Reported-by: syzbot+908886656a02769af987@...kaller.appspotmail.com
> > Cc: Andrew Pinski <pinskia@...il.com>
> > Cc: Andrey Konovalov <andreyknvl@...il.com>
> > Cc: Mark Rutland <mark.rutland@....com>
> > Cc: Will Deacon <will@...nel.org>
> > Signed-off-by: Marco Elver <elver@...gle.com>
> > ---
> >  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
> >
> >  #if defined(__SANITIZE_THREAD__)
> >  #define __no_sanitize_thread __attribute__((__no_sanitize_thread__))
> > --
> > 2.47.0.rc1.288.g06298d1525-goog
>
> Tested the change, it does fix the boot-time issue #1 from [1], but #2
> and #3 still exist.

Thanks for testing.
AFAIK #2 and #3 look like false negatives, which are tolerable (not
great, but it does not cause serious issues).

> However, perhaps, just fixing #1 is already good enough to do a revert
> of the Will's patch - at least the kernel will boot without
> false-positive reports.
>
> But I would keep a note that SW_TAGS doesn't work well with GCC until
> [1] is fully resolved.
>
> Thanks!
>
> [1] https://bugzilla.kernel.org/show_bug.cgi?id=218854