Re: [PATCH] selftests/mm: fix ptrace PEEKDATA check in memfd_secret test

[Mike Rapoport]

On Tue, Sep 08, 2026 at 10:51:11AM +0800, Hongfu Li wrote:
> From: Hongfu Li <lihongfu@xxxxxxxxxx>
> 
> try_ptrace() treats PTRACE_PEEKDATA return value as a boolean
> check. A successful read returns non-zero data (memory filled with
> 0x55), causing the test to incorrectly report PASS when secret memory
> protection is broken.
> 
> Check the return value against -1 instead. The test should only pass
> when PTRACE_PEEKDATA fails, which means secret memory protection works.
> 
> Fixes: 76fe17ef588a ("secretmem: test: add basic selftest for memfd_secret(2)")
> Signed-off-by: Hongfu Li <lihongfu@xxxxxxxxxx>

Acked-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>

> ---
>  tools/testing/selftests/mm/memfd_secret.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/mm/memfd_secret.c b/tools/testing/selftests/mm/memfd_secret.c
> index c55d84c5e613..dd08a3a1ef14 100644
> --- a/tools/testing/selftests/mm/memfd_secret.c
> +++ b/tools/testing/selftests/mm/memfd_secret.c
> @@ -145,7 +145,7 @@ static void try_ptrace(int fd, int pipefd[2])
>  		exit(KSFT_FAIL);
>  	}
>  
> -	if (ptrace(PTRACE_PEEKDATA, ppid, mem, 0))
> +	if (ptrace(PTRACE_PEEKDATA, ppid, mem, 0) == -1)
>  		exit(KSFT_PASS);
>  
>  	exit(KSFT_FAIL);
> -- 
> 2.54.0
> 
> 

-- 
Sincerely yours,
Mike.