linux-kernel - Re: [PATCH 1/2] selftests/x86/signal: Adjust the test to the kernel's altstack check

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Date:   Thu, 16 Jun 2022 16:47:34 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     "Chang S. Bae" <chang.seok.bae@...el.com>,
        linux-kselftest@...r.kernel.org, shuah@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     dave.hansen@...ux.intel.com, tglx@...utronix.de, bp@...e.de,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 1/2] selftests/x86/signal: Adjust the test to the kernel's
 altstack check

On 4/1/22 4:10 PM, Chang S. Bae wrote:
> The test assumes an insufficient altstack is allowed. Then it raises a
> signal to test the delivery failure due to an altstack overflow.
> 
> The kernel now provides an option to tweak sigaltstack()'s sanity check to
> prevent an insufficient altstack. ENOMEM is returned on the check failure.
> 
> Adjust the code to skip the test when this option is on.

Mention the option name here and in the Skip message.

> 
> Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
> Cc: linux-kselftest@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---
>   tools/testing/selftests/x86/sigaltstack.c | 12 +++++++++++-
>   1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/x86/sigaltstack.c b/tools/testing/selftests/x86/sigaltstack.c
> index f689af75e979..22a88b764a8e 100644
> --- a/tools/testing/selftests/x86/sigaltstack.c
> +++ b/tools/testing/selftests/x86/sigaltstack.c
> @@ -88,8 +88,18 @@ static void sigalrm(int sig, siginfo_t *info, void *ctx_void)
>   
>   static void test_sigaltstack(void *altstack, unsigned long size)
>   {
> -	if (setup_altstack(altstack, size))
> +	if (setup_altstack(altstack, size)) {
> +		/*
> +		 * The kernel may return ENOMEM when the altstack size
> +		 * is insufficient. Skip the test in this case.
> +		 */
> +		if (errno == ENOMEM && size < at_minstack_size) {
> +			printf("[SKIP]\tThe running kernel disallows an insufficient size.\n");

Please improve this message to clearly why it is okay to skip the test.
Mention that the option to disallowing insufficient is enabled and that
the test can't be run.


> +			return;
> +		}
> +
>   		err(1, "sigaltstack()");
> +	}
>   
>   	sigalrm_expected = (size > at_minstack_size) ? true : false;
>   
> 

With these changes:

Reviewed-by: Shuah Khan <skhan@...uxfoundation.org>

thanks,
-- Shuah