Re: [PATCH v4 07/45] kmsan: introduce __no_sanitize_memory and __no_kmsan_checks

Marco Elver
2022-07-12T14:18:22Z

On Fri, 1 Jul 2022 at 16:23, Alexander Potapenko <glider@google.com> wrote:
>
> __no_sanitize_memory is a function attribute that instructs KMSAN to
> skip a function during instrumentation. This is needed to e.g. implement
> the noinstr functions.
>
> __no_kmsan_checks is a function attribute that makes KMSAN
> ignore the uninitialized values coming from the function's
> inputs, and initialize the function's outputs.
>
> Functions marked with this attribute can't be inlined into functions
> not marked with it, and vice versa. This behavior is overridden by
> __always_inline.
>
> __SANITIZE_MEMORY__ is a macro that's defined iff the file is
> instrumented with KMSAN. This is not the same as CONFIG_KMSAN, which is
> defined for every file.
>
> Signed-off-by: Alexander Potapenko <glider@google.com>

Reviewed-by: Marco Elver <elver@google.com>

> ---
> Link: https://linux-review.googlesource.com/id/I004ff0360c918d3cd8b18767ddd1381c6d3281be
> ---
> include/linux/compiler-clang.h | 23 +++++++++++++++++++++++
> include/linux/compiler-gcc.h | 6 ++++++
> 2 files changed, 29 insertions(+)
>
> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
> index c84fec767445d..4fa0cc4cbd2c8 100644
> --- a/include/linux/compiler-clang.h
> +++ b/include/linux/compiler-clang.h
> @@ -51,6 +51,29 @@
> #define __no_sanitize_undefined
> #endif
>
> +#if __has_feature(memory_sanitizer)
> +#define __SANITIZE_MEMORY__
> +/*
> + * Unlike other sanitizers, KMSAN still inserts code into functions marked with
> + * no_sanitize("kernel-memory"). Using disable_sanitizer_instrumentation
> + * provides the behavior consistent with other __no_sanitize_ attributes,
> + * guaranteeing that __no_sanitize_memory functions remain uninstrumented.
> + */
> +#define __no_sanitize_memory __disable_sanitizer_instrumentation
> +
> +/*
> + * The __no_kmsan_checks attribute ensures that a function does not produce
> + * false positive reports by:
> + * - initializing all local variables and memory stores in this function;
> + * - skipping all shadow checks;
> + * - passing initialized arguments to this function's callees.
> + */
> +#define __no_kmsan_checks __attribute__((no_sanitize("kernel-memory")))
> +#else
> +#define __no_sanitize_memory
> +#define __no_kmsan_checks
> +#endif
> +
> /*
> * Support for __has_feature(coverage_sanitizer) was added in Clang 13 together
> * with no_sanitize("coverage"). Prior versions of Clang support coverage
> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> index a0c55eeaeaf16..63eb90eddad77 100644
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -125,6 +125,12 @@
> #define __SANITIZE_ADDRESS__
> #endif
>
> +/*
> + * GCC does not support KMSAN.
> + */
> +#define __no_sanitize_memory
> +#define __no_kmsan_checks
> +
> /*
> * Turn individual warnings and errors on and off locally, depending
> * on version.
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>