diff mbox series

[bpf-next,1/2] bpf: Fix verifier log for async callback return values

Message ID 20231009161414.235829-1-void@manifault.com
State New
Headers
Series [bpf-next,1/2] bpf: Fix verifier log for async callback return values |

Commit Message

David Vernet Oct. 9, 2023, 4:14 p.m. UTC 
  The verifier, as part of check_return_code(), verifies that async
callbacks such as from e.g. timers, will return 0. It does this by
correctly checking that R0->var_off is in tnum_const(0), which
effectively checks that it's in a range of 0. If this condition fails,
however, it prints an error message which says that the value should
have been in (0x0; 0x1). This results in possibly confusing output such
as the following in which an async callback returns 1:

At async callback the register R0 has value (0x1; 0x0) should have been
in (0x0; 0x1)

The fix is easy -- we should just pass the tnum_const(0) as the correct
range to verbose_invalid_scalar(), which will then print the following:

At async callback the register R0 has value (0x1; 0x0) should have been
in (0x0; 0x0)

Fixes: bfc6bb74e4f1 ("bpf: Implement verifier support for validation of async callbacks.")
Signed-off-by: David Vernet <void@manifault.com>
---
 kernel/bpf/verifier.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

patchwork-bot+netdevbpf@kernel.org Oct. 9, 2023, 9:20 p.m. UTC | #1 
Hello:

This series was applied to bpf/bpf.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Mon,  9 Oct 2023 11:14:13 -0500 you wrote:
> The verifier, as part of check_return_code(), verifies that async
> callbacks such as from e.g. timers, will return 0. It does this by
> correctly checking that R0->var_off is in tnum_const(0), which
> effectively checks that it's in a range of 0. If this condition fails,
> however, it prints an error message which says that the value should
> have been in (0x0; 0x1). This results in possibly confusing output such
> as the following in which an async callback returns 1:
> 
> [...]

Here is the summary with links:
  - [bpf-next,1/2] bpf: Fix verifier log for async callback return values
    https://git.kernel.org/bpf/bpf/c/829955981c55
  - [bpf-next,2/2] bpf/selftests: Add testcase for async callback return value failure
    https://git.kernel.org/bpf/bpf/c/57ddeb86b311

You are awesome, thank you!
diff mbox series

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index eed7350e15f4..9093fb74c88e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -14729,7 +14729,7 @@  static int check_return_code(struct bpf_verifier_env *env, int regno)
 	struct tnum enforce_attach_type_range = tnum_unknown;
 	const struct bpf_prog *prog = env->prog;
 	struct bpf_reg_state *reg;
-	struct tnum range = tnum_range(0, 1);
+	struct tnum range = tnum_range(0, 1), const_0 = tnum_const(0);
 	enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
 	int err;
 	struct bpf_func_state *frame = env->cur_state->frame[0];
@@ -14777,8 +14777,8 @@  static int check_return_code(struct bpf_verifier_env *env, int regno)
 			return -EINVAL;
 		}
 
-		if (!tnum_in(tnum_const(0), reg->var_off)) {
-			verbose_invalid_scalar(env, reg, &range, "async callback", "R0");
+		if (!tnum_in(const_0, reg->var_off)) {
+			verbose_invalid_scalar(env, reg, &const_0, "async callback", "R0");
 			return -EINVAL;
 		}
 		return 0;