On Mon, Dec 2, 2024 at 12:38 AM Kumar Kartikeya Dwivedi
<memxor@xxxxxxxxx> 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.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> ---
> .../selftests/bpf/progs/verifier_spill_fill.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
> index 671d9f415dbf..f5cd21326811 100644
> --- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
> +++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
> @@ -1244,4 +1244,21 @@ __naked void old_stack_misc_vs_cur_ctx_ptr(void)
> : __clobber_all);
> }
>
> +SEC("tc")
> +__description("stack_noperfmon: reject read of invalid slots")
> +__success __failure_unpriv __msg_unpriv("invalid read from stack off -8+1 size 8")
> +__caps_unpriv(CAP_BPF)
same styling nit about __success staying on a separate line
I'd actually do it this way to make it a bit more explicit that we
have custom unpriv caps:
__success
__caps_unpriv(CAP_BPF)
__failure_unpriv __msg_unpriv("...")
but it's minor
> +__naked void stack_noperfmon_reject_invalid_read(void)
> +{
> + asm volatile (" \
> + r2 = 1; \
> + r6 = r10; \
> + r6 += -8; \
> + *(u8 *)(r6 + 0) = r2; \
> + r2 = *(u64 *)(r6 + 0); \
> + r0 = 0; \
> + exit; \
> +" ::: __clobber_all);
> +}
> +
> char _license[] SEC("license") = "GPL";
> --
> 2.43.5
>
