Re: [PATCH v6 2/7] selftests: x86: test_mremap_vdso: skip if vdso is msealed

[Liam R. Howlett]

* jeffxu@xxxxxxxxxxxx <jeffxu@xxxxxxxxxxxx> [250224 12:45]:
> From: Jeff Xu <jeffxu@xxxxxxxxxxxx>
> 
> Add code to detect if the vdso is memory sealed, skip the test
> if it is.

It also skips the test if fopen fails on smaps, but maybe that's super
rare?

> 
> Signed-off-by: Jeff Xu <jeffxu@xxxxxxxxxxxx>
> ---
>  .../testing/selftests/x86/test_mremap_vdso.c  | 38 +++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/tools/testing/selftests/x86/test_mremap_vdso.c b/tools/testing/selftests/x86/test_mremap_vdso.c
> index d53959e03593..c68077c56b22 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 +56,50 @@ 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)
> +{
> +	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\n");

fork() below prints errno, should this also print errno?

> +		return 0;

I guess the logic here is that you might fail later because it's sealed
but you don't know?  Is this rare enough not to matter?

> +	}
> +
> +	if (vdso_sealed(maps)) {
> +		ksft_test_result_skip("vdso is sealed\n");
> +		return 0;
> +	}
> +

This file also has an #ifdef __i386__ later,  Using it here would
prevent unnecessary scanning of the maps file.  Probably not a big deal?

Do you need to close the maps file?

>  	child = fork();
>  	if (child == -1)
>  		ksft_exit_fail_msg("failed to fork (%d): %m\n", errno);
> -- 
> 2.48.1.601.g30ceb7b040-goog
>