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From:   Marco Elver <elver@google.com>
Date:   Fri, 9 Sep 2022 10:43:54 +0200
Message-ID: <CANpmjNOz9bomQv=Zem6kw9xamhp1yPKf3iCrVvhkzHxE2pcp0A@mail.gmail.com>
Subject: Re: [PATCH v2 2/3] kcsan: Instrument memcpy/memset/memmove with newer Clang
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     "Paul E. McKenney" <paulmck@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Potapenko <glider@google.com>,
        Boqun Feng <boqun.feng@gmail.com>, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        llvm@lists.linux.dev, Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-s390@vger.kernel.org, stable@vger.kernel.org
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On Fri, 9 Sept 2022 at 10:38, Dmitry Vyukov <dvyukov@google.com> wrote:
>
> On Fri, 9 Sept 2022 at 09:38, Marco Elver <elver@google.com> wrote:
> >
> > With Clang version 16+, -fsanitize=thread will turn
> > memcpy/memset/memmove calls in instrumented functions into
> > __tsan_memcpy/__tsan_memset/__tsan_memmove calls respectively.
> >
> > Add these functions to the core KCSAN runtime, so that we (a) catch data
> > races with mem* functions, and (b) won't run into linker errors with
> > such newer compilers.
> >
> > Cc: stable@vger.kernel.org # v5.10+
> > Signed-off-by: Marco Elver <elver@google.com>
> > ---
> > v2:
> > * Fix for architectures which do not provide their own
> >   memcpy/memset/memmove and instead use the generic versions in
> >   lib/string. In this case we'll just alias the __tsan_ variants.
> > ---
> >  kernel/kcsan/core.c | 39 +++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 39 insertions(+)
> >
> > diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> > index fe12dfe254ec..4015f2a3e7f6 100644
> > --- a/kernel/kcsan/core.c
> > +++ b/kernel/kcsan/core.c
> > @@ -18,6 +18,7 @@
> >  #include <linux/percpu.h>
> >  #include <linux/preempt.h>
> >  #include <linux/sched.h>
> > +#include <linux/string.h>
> >  #include <linux/uaccess.h>
> >
> >  #include "encoding.h"
> > @@ -1308,3 +1309,41 @@ noinline void __tsan_atomic_signal_fence(int memorder)
> >         }
> >  }
> >  EXPORT_SYMBOL(__tsan_atomic_signal_fence);
> > +
> > +#ifdef __HAVE_ARCH_MEMSET
> > +void *__tsan_memset(void *s, int c, size_t count);
> > +noinline void *__tsan_memset(void *s, int c, size_t count)
> > +{
> > +       check_access(s, count, KCSAN_ACCESS_WRITE, _RET_IP_);
>
> These can use large sizes, does it make sense to truncate it to
> MAX_ENCODABLE_SIZE?

Hmm, good point - that way it can still set up watchpoints on them.
I'll do a v3.