Re: [PATCH 2/5] x86/uaccess: instrument copy_from_user_nmi()

Peter Zijlstra
2022-11-02T12:53:01Z

On Wed, Nov 02, 2022 at 12:06:08PM +0100, Alexander Potapenko wrote:
> Make sure usercopy hooks from linux/instrumented.h are invoked for
> copy_from_user_nmi().
> This fixes KMSAN false positives reported when dumping opcodes for a
> stack trace.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: x86@kernel.org
> Signed-off-by: Alexander Potapenko <glider@google.com>

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

> ---
> arch/x86/lib/usercopy.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
> index f1bb186171562..24b48af274173 100644
> --- a/arch/x86/lib/usercopy.c
> +++ b/arch/x86/lib/usercopy.c
> @@ -6,6 +6,7 @@
>
> #include <linux/uaccess.h>
> #include <linux/export.h>
> +#include <linux/instrumented.h>
>
> #include <asm/tlbflush.h>
>
> @@ -44,7 +45,9 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
> * called from other contexts.
> */
> pagefault_disable();
> + instrument_copy_from_user_before(to, from, n);
> ret = raw_copy_from_user(to, from, n);
> + instrument_copy_from_user_after(to, from, n, ret);
> pagefault_enable();
>
> return ret;
> --
> 2.38.1.273.g43a17bfeac-goog
>