Re: [PATCH v7 2/7] selftests: x86: test_mremap_vdso: skip if vdso is msealed

[Lorenzo Stoakes]

On Mon, Feb 24, 2025 at 10:52:41PM +0000, jeffxu@xxxxxxxxxxxx wrote:
> From: Jeff Xu <jeffxu@xxxxxxxxxxxx>
>
> Add code to detect if the vdso is memory sealed, skip the test
> if it is.

I feel this is a little succinct of a commit message, but I guess it gets to the
heart of what you're doing here.

Fundamentally I mean it makes sense, but I'm concerned that x86 has a test
-expliictly checking- whether mremap() of VDSO is possible - are there cases
where x86 might want to do this internal to the kernel?

I guess not since this is essentially a userland self test and probably
asserting you can do this in the way rr, etc. do.

>
> Signed-off-by: Jeff Xu <jeffxu@xxxxxxxxxxxx>
> Reviewed-by: Kees Cook <kees@xxxxxxxxxx>

Anyway, this aside, this looks fine, aside from nit below, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>

> ---
>  .../testing/selftests/x86/test_mremap_vdso.c  | 43 +++++++++++++++++++
>  1 file changed, 43 insertions(+)
>
> diff --git a/tools/testing/selftests/x86/test_mremap_vdso.c b/tools/testing/selftests/x86/test_mremap_vdso.c
> index d53959e03593..94bee6e0c813 100644
> --- a/tools/testing/selftests/x86/test_mremap_vdso.c
> +++ b/tools/testing/selftests/x86/test_mremap_vdso.c
> @@ -14,6 +14,7 @@
>  #include <errno.h>
>  #include <unistd.h>
>  #include <string.h>
> +#include <stdbool.h>
>
>  #include <sys/mman.h>
>  #include <sys/auxv.h>
> @@ -55,13 +56,55 @@ static int try_to_remap(void *vdso_addr, unsigned long size)
>
>  }
>
> +#define VDSO_NAME "[vdso]"
> +#define VMFLAGS "VmFlags:"
> +#define MSEAL_FLAGS "sl"
> +#define MAX_LINE_LEN 512
> +
> +bool vdso_sealed(FILE *maps)

Should be static?

> +{
> +	char line[MAX_LINE_LEN];
> +	bool has_vdso = false;
> +
> +	while (fgets(line, sizeof(line), maps)) {
> +		if (strstr(line, VDSO_NAME))
> +			has_vdso = true;
> +
> +		if (has_vdso && !strncmp(line, VMFLAGS, strlen(VMFLAGS))) {
> +			if (strstr(line, MSEAL_FLAGS))
> +				return true;
> +
> +			return false;
> +		}
> +	}
> +
> +	return false;
> +}
> +
>  int main(int argc, char **argv, char **envp)
>  {
>  	pid_t child;
> +	FILE *maps;
>
>  	ksft_print_header();
>  	ksft_set_plan(1);
>
> +	maps = fopen("/proc/self/smaps", "r");
> +	if (!maps) {
> +		ksft_test_result_skip(
> +			"Could not open /proc/self/smaps, errno=%d\n",
> +			 errno);
> +
> +		return 0;
> +	}
> +
> +	if (vdso_sealed(maps)) {
> +		ksft_test_result_skip("vdso is sealed\n");
> +		return 0;
> +	}
> +
> +	fclose(maps);
> +
>  	child = fork();
>  	if (child == -1)
>  		ksft_exit_fail_msg("failed to fork (%d): %m\n", errno);
> --
> 2.48.1.658.g4767266eb4-goog
>