[bpf-next,v3,4/5] selftests/bpf: Add test for reading from STACK_INVALID slots

Commit Message

Kumar Kartikeya Dwivedi Dec. 2, 2024, 8:38 a.m. UTC

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 <[e-mail]>
---
 .../selftests/bpf/progs/verifier_spill_fill.c   | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

Comments

Eduard Zingerman Dec. 2, 2024, 10:50 p.m. UTC | #1

On Mon, 2024-12-02 at 00:38 -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.
> 
> Signed-off-by: Kumar Kartikeya Dwivedi <[e-mail]>
> ---

Acked-by: Eduard Zingerman <[e-mail]>

[...]

Andrii Nakryiko Dec. 3, 2024, 12:16 a.m. UTC | #2

On Mon, Dec 2, 2024 at 12:38 AM Kumar Kartikeya Dwivedi
<[e-mail]> 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 <[e-mail]>
> ---
>  .../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
>

Patch

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)
+__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";