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

[Peter Zijlstra]

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@xxxxxxxxxxxxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>

Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>

> ---
>  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
>