Re: [PATCH v2 2/3] instrumented.h: add instrument_memcpy_before, instrument_memcpy_after

[Marco Elver]

On Wed, 20 Mar 2024 at 11:19, Alexander Potapenko <glider@xxxxxxxxxx> wrote:
>
> Bug detection tools based on compiler instrumentation may miss memory
> accesses in custom memcpy implementations (such as copy_mc_to_kernel).
> Provide instrumentation hooks that tell KASAN, KCSAN, and KMSAN about
> such accesses.
>
> Link: https://lore.kernel.org/all/3b7dbd88-0861-4638-b2d2-911c97a4cadf@xxxxxxxxxxxxxxxxxxx/
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>

Reviewed-by: Marco Elver <elver@xxxxxxxxxx>

> ---
>  v2: fix a copypasto in a comment spotted by Linus
> ---
>  include/linux/instrumented.h | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
>
> diff --git a/include/linux/instrumented.h b/include/linux/instrumented.h
> index 1b608e00290aa..711a1f0d1a735 100644
> --- a/include/linux/instrumented.h
> +++ b/include/linux/instrumented.h
> @@ -147,6 +147,41 @@ instrument_copy_from_user_after(const void *to, const void __user *from,
>         kmsan_unpoison_memory(to, n - left);
>  }
>
> +/**
> + * instrument_memcpy_before - add instrumentation before non-instrumented memcpy
> + * @to: destination address
> + * @from: source address
> + * @n: number of bytes to copy
> + *
> + * Instrument memory accesses that happen in custom memcpy implementations. The
> + * instrumentation should be inserted before the memcpy call.
> + */
> +static __always_inline void instrument_memcpy_before(void *to, const void *from,
> +                                                    unsigned long n)
> +{
> +       kasan_check_write(to, n);
> +       kasan_check_read(from, n);
> +       kcsan_check_write(to, n);
> +       kcsan_check_read(from, n);
> +}
> +
> +/**
> + * instrument_memcpy_after - add instrumentation after non-instrumented memcpy
> + * @to: destination address
> + * @from: source address
> + * @n: number of bytes to copy
> + * @left: number of bytes not copied (if known)
> + *
> + * Instrument memory accesses that happen in custom memcpy implementations. The
> + * instrumentation should be inserted after the memcpy call.
> + */
> +static __always_inline void instrument_memcpy_after(void *to, const void *from,
> +                                                   unsigned long n,
> +                                                   unsigned long left)
> +{
> +       kmsan_memmove(to, from, n - left);
> +}
> +
>  /**
>   * instrument_get_user() - add instrumentation to get_user()-like macros
>   * @to: destination variable, may not be address-taken
> --
> 2.44.0.291.gc1ea87d7ee-goog
>