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

[Jeff Xu]

On Mon, Feb 24, 2025 at 10:15 PM Lorenzo Stoakes
<lorenzo.stoakes@xxxxxxxxxx> wrote:
>
> 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?
>
sure.

> > +{
> > +     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
> >