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

[Eduard Zingerman <eddyz87@gmail.com>]

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

>  {
> -	__u64 caps = 0;
>  	int ret;
>  
>  	/* In case CAP_BPF and CAP_PERFMON is not set */
> -	ret = cap_enable_effective(1ULL << CAP_BPF | 1ULL << CAP_NET_ADMIN, &caps);
> +	ret = cap_enable_effective(1ULL << CAP_BPF | 1ULL << CAP_NET_ADMIN, caps);
>  	if (!ASSERT_OK(ret, "set_cap_bpf_cap_net_admin"))
> -		return;
> +		return -EINVAL;
>  	ret = cap_disable_effective(1ULL << CAP_SYS_ADMIN | 1ULL << CAP_PERFMON, NULL);
>  	if (!ASSERT_OK(ret, "disable_cap_sys_admin"))
> +		return -EINVAL;
> +	return 0;
> +}

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