Re: [PATCH 1/8] kcsan: Add Kernel Concurrency Sanitizer infrastructure

[Boqun Feng <boqun.feng@gmail.com>]

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On Wed, Oct 16, 2019 at 12:06:51PM +0200, Marco Elver wrote:
> On Wed, 16 Oct 2019 at 11:42, Boqun Feng <boqun.feng@gmail.com> wrote:
> >
> > Hi Marco,
> >
> > On Wed, Oct 16, 2019 at 10:39:52AM +0200, Marco Elver wrote:
> > [...]
> > > --- /dev/null
> > > +++ b/kernel/kcsan/kcsan.c
> > > @@ -0,0 +1,81 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +
> > > +/*
> > > + * The Kernel Concurrency Sanitizer (KCSAN) infrastructure. For more info please
> > > + * see Documentation/dev-tools/kcsan.rst.
> > > + */
> > > +
> > > +#include <linux/export.h>
> > > +
> > > +#include "kcsan.h"
> > > +
> > > +/*
> > > + * Concurrency Sanitizer uses the same instrumentation as Thread Sanitizer.
> >
> > Is there any documentation on the instrumentation? Like a complete list
> > for all instrumentation functions plus a description of where the
> > compiler will use those functions. Yes, the names of the below functions
> > are straightforward, but an accurate doc on the instrumentation will
> > cerntainly help people review KCSAN.
> 
> As far as I'm aware neither GCC nor Clang have documentation on the
> emitted instrumentation that we could reference (other than look into
> the compiler passes).
> 

Yeah, I don't find them either, which makes me surprised, because I
think the thread sanitizer has been there for a while...

> However it is as straightforward as it seems: the compiler emits
> instrumentation calls for all loads and stores that the compiler
> generates; inline asm is not instrumented. I will add a comment to
> that effect for v2.
> 

Or you can push the compiler people to document it, and we can simply
reference it in kernel ;-)

Regards,
Boqun

> Thanks,
> -- Marco
> 
> > Regards,
> > Boqun
> >
> > > + */
> > > +
> > > +#define DEFINE_TSAN_READ_WRITE(size)                                           \
> > > +     void __tsan_read##size(void *ptr)                                      \
> > > +     {                                                                      \
> > > +             __kcsan_check_access(ptr, size, false);                        \
> > > +     }                                                                      \
> > > +     EXPORT_SYMBOL(__tsan_read##size);                                      \
> > > +     void __tsan_write##size(void *ptr)                                     \
> > > +     {                                                                      \
> > > +             __kcsan_check_access(ptr, size, true);                         \
> > > +     }                                                                      \
> > > +     EXPORT_SYMBOL(__tsan_write##size)
> > > +
> > > +DEFINE_TSAN_READ_WRITE(1);
> > > +DEFINE_TSAN_READ_WRITE(2);
> > > +DEFINE_TSAN_READ_WRITE(4);
> > > +DEFINE_TSAN_READ_WRITE(8);
> > > +DEFINE_TSAN_READ_WRITE(16);
> > > +
> > > +/*
> > > + * Not all supported compiler versions distinguish aligned/unaligned accesses,
> > > + * but e.g. recent versions of Clang do.
> > > + */
> > > +#define DEFINE_TSAN_UNALIGNED_READ_WRITE(size)                                 \
> > > +     void __tsan_unaligned_read##size(void *ptr)                            \
> > > +     {                                                                      \
> > > +             __kcsan_check_access(ptr, size, false);                        \
> > > +     }                                                                      \
> > > +     EXPORT_SYMBOL(__tsan_unaligned_read##size);                            \
> > > +     void __tsan_unaligned_write##size(void *ptr)                           \
> > > +     {                                                                      \
> > > +             __kcsan_check_access(ptr, size, true);                         \
> > > +     }                                                                      \
> > > +     EXPORT_SYMBOL(__tsan_unaligned_write##size)
> > > +
> > > +DEFINE_TSAN_UNALIGNED_READ_WRITE(2);
> > > +DEFINE_TSAN_UNALIGNED_READ_WRITE(4);
> > > +DEFINE_TSAN_UNALIGNED_READ_WRITE(8);
> > > +DEFINE_TSAN_UNALIGNED_READ_WRITE(16);
> > > +
> > > +void __tsan_read_range(void *ptr, size_t size)
> > > +{
> > > +     __kcsan_check_access(ptr, size, false);
> > > +}
> > > +EXPORT_SYMBOL(__tsan_read_range);
> > > +
> > > +void __tsan_write_range(void *ptr, size_t size)
> > > +{
> > > +     __kcsan_check_access(ptr, size, true);
> > > +}
> > > +EXPORT_SYMBOL(__tsan_write_range);
> > > +
> > > +/*
> > > + * The below are not required KCSAN, but can still be emitted by the compiler.
> > > + */
> > > +void __tsan_func_entry(void *call_pc)
> > > +{
> > > +}
> > > +EXPORT_SYMBOL(__tsan_func_entry);
> > > +void __tsan_func_exit(void)
> > > +{
> > > +}
> > > +EXPORT_SYMBOL(__tsan_func_exit);
> > > +void __tsan_init(void)
> > > +{
> > > +}
> > > +EXPORT_SYMBOL(__tsan_init);
> > [...]

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