linux-kernel - Re: [PATCH v7 2/7] selftests: x86: test_mremap

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Message-ID: <f09fa8de-468b-40bb-aee3-a33ba0678dcd@lucifer.local>
Date: Wed, 26 Feb 2025 05:58:23 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Jeff Xu <jeffxu@...omium.org>
Cc: akpm@...ux-foundation.org, keescook@...omium.org, jannh@...gle.com,
        torvalds@...ux-foundation.org, vbabka@...e.cz, Liam.Howlett@...cle.com,
        adhemerval.zanella@...aro.org, oleg@...hat.com, avagin@...il.com,
        benjamin@...solutions.net, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org, linux-mm@...ck.org,
        jorgelo@...omium.org, sroettger@...gle.com, hch@....de,
        ojeda@...nel.org, thomas.weissschuh@...utronix.de, adobriyan@...il.com,
        johannes@...solutions.net, pedro.falcato@...il.com, hca@...ux.ibm.com,
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        enh@...gle.com, rientjes@...gle.com, groeck@...omium.org,
        mpe@...erman.id.au, aleksandr.mikhalitsyn@...onical.com,
        mike.rapoport@...il.com, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v7 2/7] selftests: x86: test_mremap_vdso: skip if vdso is
 msealed

On Tue, Feb 25, 2025 at 02:37:46PM -0800, Jeff Xu wrote:
> On Mon, Feb 24, 2025 at 10:15 PM Lorenzo Stoakes
> <lorenzo.stoakes@...cle.com> wrote:
> >
> > On Mon, Feb 24, 2025 at 10:52:41PM +0000, jeffxu@...omium.org wrote:
> > > From: Jeff Xu <jeffxu@...omium.org>
> > >
> > > 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@...omium.org>
> > > Reviewed-by: Kees Cook <kees@...nel.org>
> >
> > Anyway, this aside, this looks fine, aside from nit below, so:
> >
> > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> >
> > > ---
> > >  .../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.

Thanks! :)

>
> > > +{
> > > +     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
> > >