Re: [PATCH 7/8] locking/atomics, kcsan: Add KCSAN instrumentation

Marco Elver
2019-10-16T11:47:44Z

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