Re: [PATCH bpf-next v2 3/4] selftests/bpf: Add test for reading from STACK_INVALID slots

[Eduard Zingerman <eddyz87@gmail.com>]

On Thu, 2024-11-28 at 02:57 +0100, Kumar Kartikeya Dwivedi wrote:
> On Thu, 28 Nov 2024 at 02:50, Eduard Zingerman <eddyz87@gmail.com> wrote:
> > 
> > On Wed, 2024-11-27 at 13:20 -0800, Kumar Kartikeya Dwivedi wrote:
> > > Ensure that when CAP_PERFMON is dropped, and the verifier sees
> > > allow_ptr_leaks as false, we are not permitted to read from a
> > > STACK_INVALID slot. Without the fix, the test will report unexpected
> > > success in loading.
> > > 
> > > Since we need to control the capabilities when loading this test to only
> > > retain CAP_BPF, refactor support added to do the same for
> > > test_verifier_mtu and reuse it for this selftest to avoid copy-paste.
> > > 
> > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> > > ---
> > >  .../selftests/bpf/prog_tests/verifier.c       | 41 ++++++++++++++++---
> > >  .../bpf/progs/verifier_stack_noperfmon.c      | 21 ++++++++++
> > >  2 files changed, 56 insertions(+), 6 deletions(-)
> > >  create mode 100644 tools/testing/selftests/bpf/progs/verifier_stack_noperfmon.c
> > > 
> > > diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
> > > index d9f65adb456b..aaf4324e8ef0 100644
> > > --- a/tools/testing/selftests/bpf/prog_tests/verifier.c
> > > +++ b/tools/testing/selftests/bpf/prog_tests/verifier.c
> > > @@ -63,6 +63,7 @@
> > >  #include "verifier_prevent_map_lookup.skel.h"
> > >  #include "verifier_private_stack.skel.h"
> > >  #include "verifier_raw_stack.skel.h"
> > > +#include "verifier_stack_noperfmon.skel.h"
> > >  #include "verifier_raw_tp_writable.skel.h"
> > >  #include "verifier_reg_equal.skel.h"
> > >  #include "verifier_ref_tracking.skel.h"
> > > @@ -226,22 +227,50 @@ void test_verifier_xdp_direct_packet_access(void) { RUN(verifier_xdp_direct_pack
> > >  void test_verifier_bits_iter(void) { RUN(verifier_bits_iter); }
> > >  void test_verifier_lsm(void)                  { RUN(verifier_lsm); }
> > > 
> > > -void test_verifier_mtu(void)
> > > +static int test_verifier_disable_caps(__u64 *caps)
> > 
> > The original thread [0] discusses __caps_unpriv macro.
> > I'd prefer such macro over these changes to prog_tests/verifier.c,
> > were there any technical problems with code suggested in [0]?
> > 
> > [0] https://lore.kernel.org/bpf/a1e48f5d9ae133e19adc6adf27e19d585e06bab4.camel@gmail.com/#t
> > 
> 
> I think that patch worked as well, but I got to look at this now after
> all these months, and concluded that
> what Daniel did in
> https://lore.kernel.org/bpf/20241021152809.33343-5-daniel@iogearbox.net
> was also
> acceptable and preferred.
> 
> I can add your patch to this set and respin, or post a follow-up converting
> test_verifier_mtu to it as well. Whatever is preferred.

Patch #1 would need a respin because the comment for mark_stack_slot_misc() needs fixing.
If you agree with adding __caps_unpriv, could you please make it a part of v3?

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