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From:   Marco Elver <elver@google.com>
Date:   Wed, 16 Oct 2019 13:47:30 +0200
Message-ID: <CANpmjNMww9EX_WqAfWbQk8VG=DghLL7f=Otsx2=bs5sLh-VERQ@mail.gmail.com>
Subject: Re: [PATCH 7/8] locking/atomics, kcsan: Add KCSAN instrumentation
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     LKMM Maintainers -- Akira Yokosawa <akiyks@gmail.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Alexander Potapenko <glider@google.com>,
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On Wed, 16 Oct 2019 at 13:18, Mark Rutland <mark.rutland@arm.com> wrote:
>
> Hi Marco,
>
> On Wed, Oct 16, 2019 at 10:39:58AM +0200, Marco Elver wrote:
> > This adds KCSAN instrumentation to atomic-instrumented.h.
> >
> > Signed-off-by: Marco Elver <elver@google.com>
> > ---
> >  include/asm-generic/atomic-instrumented.h | 192 +++++++++++++++++++++-
> >  scripts/atomic/gen-atomic-instrumented.sh |   9 +-
> >  2 files changed, 199 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/asm-generic/atomic-instrumented.h b/include/asm-generic/atomic-instrumented.h
> > index e8730c6b9fe2..9e487febc610 100644
> > --- a/include/asm-generic/atomic-instrumented.h
> > +++ b/include/asm-generic/atomic-instrumented.h
> > @@ -19,11 +19,13 @@
> >
> >  #include <linux/build_bug.h>
> >  #include <linux/kasan-checks.h>
> > +#include <linux/kcsan-checks.h>
> >
> >  static inline int
> >  atomic_read(const atomic_t *v)
> >  {
> >       kasan_check_read(v, sizeof(*v));
> > +     kcsan_check_atomic(v, sizeof(*v), false);
>
> For legibility and consistency with kasan, it would be nicer to avoid
> the bool argument here and have kcsan_check_atomic_{read,write}()
> helpers...
>
> > diff --git a/scripts/atomic/gen-atomic-instrumented.sh b/scripts/atomic/gen-atomic-instrumented.sh
> > index e09812372b17..c0553743a6f4 100755
> > --- a/scripts/atomic/gen-atomic-instrumented.sh
> > +++ b/scripts/atomic/gen-atomic-instrumented.sh
> > @@ -12,15 +12,20 @@ gen_param_check()
> >       local type="${arg%%:*}"
> >       local name="$(gen_param_name "${arg}")"
> >       local rw="write"
> > +     local is_write="true"
> >
> >       case "${type#c}" in
> >       i) return;;
> >       esac
> >
> >       # We don't write to constant parameters
> > -     [ ${type#c} != ${type} ] && rw="read"
> > +     if [ ${type#c} != ${type} ]; then
> > +             rw="read"
> > +             is_write="false"
> > +     fi
> >
> >       printf "\tkasan_check_${rw}(${name}, sizeof(*${name}));\n"
> > +     printf "\tkcsan_check_atomic(${name}, sizeof(*${name}), ${is_write});\n"
>
> ... which would also simplify this.
>
> Though as below, we might want to wrap both in a helper local to
> atomic-instrumented.h.
>
> >  }
> >
> >  #gen_param_check(arg...)
> > @@ -108,6 +113,7 @@ cat <<EOF
> >  ({                                                                   \\
> >       typeof(ptr) __ai_ptr = (ptr);                                   \\
> >       kasan_check_write(__ai_ptr, ${mult}sizeof(*__ai_ptr));          \\
> > +     kcsan_check_atomic(__ai_ptr, ${mult}sizeof(*__ai_ptr), true);   \\
> >       arch_${xchg}(__ai_ptr, __VA_ARGS__);                            \\
> >  })
> >  EOF
> > @@ -148,6 +154,7 @@ cat << EOF
> >
> >  #include <linux/build_bug.h>
> >  #include <linux/kasan-checks.h>
> > +#include <linux/kcsan-checks.h>
>
> We could add the following to this preamble:
>
> static inline void __atomic_check_read(const volatile void *v, size_t size)
> {
>         kasan_check_read(v, sizeof(*v));
>         kcsan_check_atomic(v, sizeof(*v), false);
> }
>
> static inline void __atomic_check_write(const volatile void *v, size_t size)
> {
>         kasan_check_write(v, sizeof(*v));
>         kcsan_check_atomic(v, sizeof(*v), true);
> }
>
> ... and only have the one call in each atomic wrapper.
>
> Otherwise, this looks good to me.

Thanks, incorporated suggestions for v2: for readability rename
kcsan_check_access -> kcsan_check_{read,write}, and for
atomic-instrumented.h, adding the suggested preamble.

Thanks,
-- Marco