[LTP] [PATCH v2] syscalls/userfaultfd01: add hint about unprivileged_userfaultfd

[Li Wang]

On Mon, Jan 6, 2020 at 5:10 PM Yang Xu <xuyang2018.jy@cn.fujitsu.com> wrote:

> Hi Li
> >
> >
> > On Wed, Dec 18, 2019 at 12:02 PM Yang Xu <xuyang2018.jy@cn.fujitsu.com
> > <mailto:xuyang2018.jy@cn.fujitsu.com>> wrote:
> >
> >     Since commit cefdca0a86be ("userfaultfd/sysctl: add
> >     vm.unprivileged_userfaultfd").
> >     , it adds a global sysctl knob "vm.unprivileged_userfaultfd" to
> >     control whether
> >     unprivileged users can use the userfaultfd system calls. Set this to
> >     1 to allow
> >     unprivileged users to use the userfaultfd system calls, or set this
> >     to 0 to
> >     restrict userfaultfd to only privileged users (with SYS_CAP_PTRACE
> >     capability). The
> >     default value is 1. Add hint about it.
> >
> >
> > Can we do the "vm.unprivileged_userfaultfd" check in the setup() and do
> > set to 1 if it exists?
> I remembered Jan Stancek has a patch about bpf hint about
> unprivileged_bpf_disabled, I do as same as that patch did.
>

I just echo the nob file "unprivileged_bpf_disabled" and find it can't be
changed at runtime. So if the "vm.unprivileged_userfaultfd" is like this
behavior too, probably we can only do TCONF as your original patch. AnywayI
will take a close look at the kernel commit later.

# cat /proc/sys/kernel/unprivileged_bpf_disabled
1
# echo 0 > /proc/sys/kernel/unprivileged_bpf_disabled
-bash: echo: write error: Invalid argument



>
> Also, month agos about acct02 discussion, Cyril points about adjusting
> the threshold value of resume and suppend to make case passes.
>
> So, I have a question that we have unified standards about these cases
> (bpf, acct02, affected by sysctl)? Report TCONF or modify argument to
> make case passes?
>
> @Cyril and @Jan Stancek What do you think about it?
>
> > And maybe we need more tests for the global sysctl knob
> > "vm.unprivileged_userfaultfd".Eeven though we don't have case to test
> unprivileged_bpf_disabled. I
> still think testing unprivileged_userfaultfd is meaningful and we can
> begin with it.
>
> Best Regards
> Yang Xu
> >
> >
> >     Signed-off-by: Yang Xu <xuyang2018.jy@cn.fujitsu.com
> >     <mailto:xuyang2018.jy@cn.fujitsu.com>>
> >     ---
> >       .../syscalls/userfaultfd/userfaultfd01.c      | 19
> +++++++++++++------
> >       1 file changed, 13 insertions(+), 6 deletions(-)
> >
> >     diff --git a/testcases/kernel/syscalls/userfaultfd/userfaultfd01.c
> >     b/testcases/kernel/syscalls/userfaultfd/userfaultfd01.c
> >     index a5e142209..4e178b4f8 100644
> >     --- a/testcases/kernel/syscalls/userfaultfd/userfaultfd01.c
> >     +++ b/testcases/kernel/syscalls/userfaultfd/userfaultfd01.c
> >     @@ -82,12 +82,19 @@ static void run(void)
> >
> >              set_pages();
> >
> >     -       uffd = sys_userfaultfd(O_CLOEXEC | O_NONBLOCK);
> >     -
> >     -       if (uffd == -1)
> >     -               tst_brk(TBROK | TERRNO,
> >     -                       "Could not create userfault file
> descriptor");
> >     -
> >     +       TEST(sys_userfaultfd(O_CLOEXEC | O_NONBLOCK));
> >     +
> >     +       if (TST_RET == -1) {
> >     +               if (TST_ERR == EPERM) {
> >     +                       tst_res(TCONF, "Hint: check
> >     /proc/sys/vm/unprivileged_userfaultfd");
> >     +                       tst_brk(TCONF | TTERRNO,
> >     +                               "userfaultfd() requires
> >     CAP_SYS_PTRACE on this system");
> >     +               } else
> >     +                       tst_brk(TBROK | TTERRNO,
> >     +                               "Could not create userfault file
> >     descriptor");
> >     +       }
> >     +
> >     +       uffd = TST_RET;
> >              uffdio_api.api = UFFD_API;
> >              uffdio_api.features = 0;
> >              SAFE_IOCTL(uffd, UFFDIO_API, &uffdio_api);
> >     --
> >     2.18.0
> >
> >
> >
> >
> >     --
> >     Mailing list info: https://lists.linux.it/listinfo/ltp
> >
> >
> >
> > --
> > Regards,
> > Li Wang
>
>
>

-- 
Regards,
Li Wang
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