Re: [PATCH v2 3/3] x86: call instrumentation hooks from copy_mc.c

[Marco Elver]

On Wed, 20 Mar 2024 at 11:19, Alexander Potapenko <glider@xxxxxxxxxx> wrote:
>
> Memory accesses in copy_mc_to_kernel() and copy_mc_to_user() are performed
> by assembly routines and are invisible to KASAN, KCSAN, and KMSAN.
> Add hooks from instrumentation.h to tell the tools these functions have
> memcpy/copy_from_user semantics.
>
> The call to copy_mc_fragile() in copy_mc_fragile_handle_tail() is left
> intact, because the latter is only called from the assembly implementation
> of copy_mc_fragile(), so the memory accesses in it are covered by the
> instrumentation in copy_mc_to_kernel() and copy_mc_to_user().
>
> Link: https://lore.kernel.org/all/3b7dbd88-0861-4638-b2d2-911c97a4cadf@xxxxxxxxxxxxxxxxxxx/
> Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>

Reviewed-by: Marco Elver <elver@xxxxxxxxxx>

> ---
> v2:
>  - as requested by Linus Torvalds, move the instrumentation outside the
>    uaccess section
> ---
>  arch/x86/lib/copy_mc.c | 21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/lib/copy_mc.c b/arch/x86/lib/copy_mc.c
> index 6e8b7e600def5..97e88e58567bf 100644
> --- a/arch/x86/lib/copy_mc.c
> +++ b/arch/x86/lib/copy_mc.c
> @@ -4,6 +4,7 @@
>  #include <linux/jump_label.h>
>  #include <linux/uaccess.h>
>  #include <linux/export.h>
> +#include <linux/instrumented.h>
>  #include <linux/string.h>
>  #include <linux/types.h>
>
> @@ -61,10 +62,20 @@ unsigned long copy_mc_enhanced_fast_string(void *dst, const void *src, unsigned
>   */
>  unsigned long __must_check copy_mc_to_kernel(void *dst, const void *src, unsigned len)
>  {
> -       if (copy_mc_fragile_enabled)
> -               return copy_mc_fragile(dst, src, len);
> -       if (static_cpu_has(X86_FEATURE_ERMS))
> -               return copy_mc_enhanced_fast_string(dst, src, len);
> +       unsigned long ret;
> +
> +       if (copy_mc_fragile_enabled) {
> +               instrument_memcpy_before(dst, src, len);
> +               ret = copy_mc_fragile(dst, src, len);
> +               instrument_memcpy_after(dst, src, len, ret);
> +               return ret;
> +       }
> +       if (static_cpu_has(X86_FEATURE_ERMS)) {
> +               instrument_memcpy_before(dst, src, len);
> +               ret = copy_mc_enhanced_fast_string(dst, src, len);
> +               instrument_memcpy_after(dst, src, len, ret);
> +               return ret;
> +       }
>         memcpy(dst, src, len);
>         return 0;
>  }
> @@ -75,6 +86,7 @@ unsigned long __must_check copy_mc_to_user(void __user *dst, const void *src, un
>         unsigned long ret;
>
>         if (copy_mc_fragile_enabled) {
> +               instrument_copy_to_user(dst, src, len);
>                 __uaccess_begin();
>                 ret = copy_mc_fragile((__force void *)dst, src, len);
>                 __uaccess_end();
> @@ -82,6 +94,7 @@ unsigned long __must_check copy_mc_to_user(void __user *dst, const void *src, un
>         }
>
>         if (static_cpu_has(X86_FEATURE_ERMS)) {
> +               instrument_copy_to_user(dst, src, len);
>                 __uaccess_begin();
>                 ret = copy_mc_enhanced_fast_string((__force void *)dst, src, len);
>                 __uaccess_end();
> --
> 2.44.0.291.gc1ea87d7ee-goog
>