From: Eduard Zingerman <eddyz87@gmail.com>
To: Andrii Nakryiko <andrii@kernel.org>,
bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
martin.lau@kernel.org
Cc: kernel-team@meta.com
Subject: Re: [PATCH v2 bpf-next 07/10] selftests/bpf: validate zero preservation for sub-slot loads
Date: Tue, 21 Nov 2023 18:20:28 +0200 [thread overview]
Message-ID: <0aea72de9d5d283be329e1f95fa8373bcba5e86a.camel@gmail.com> (raw)
In-Reply-To: <20231121002221.3687787-8-andrii@kernel.org>
On Mon, 2023-11-20 at 16:22 -0800, Andrii Nakryiko wrote:
[...]
> +SEC("raw_tp")
> +__log_level(2)
> +__success
> +__naked void partial_stack_load_preserves_zeros(void)
> +{
> + asm volatile (
> + /* fp-8 is all STACK_ZERO */
> + "*(u64 *)(r10 -8) = 0;"
This fails when compiled with llvm-16, bpf st assembly support is only
present in llvm-18. If we want to preserve support for llvm-16 this
test would require ifdefs or the following patch:
@@ -3,6 +3,7 @@
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
+#include "../../../include/linux/filter.h"
#include "bpf_misc.h"
struct {
@@ -510,7 +511,7 @@ __naked void partial_stack_load_preserves_zeros(void)
{
asm volatile (
/* fp-8 is all STACK_ZERO */
- "*(u64 *)(r10 -8) = 0;"
+ ".8byte %[fp8_st_zero];"
/* fp-16 is const zero register */
"r0 = 0;"
@@ -559,7 +560,8 @@ __naked void partial_stack_load_preserves_zeros(void)
"r0 = 0;"
"exit;"
:
- : __imm_ptr(single_byte_buf)
+ : __imm_ptr(single_byte_buf),
+ __imm_insn(fp8_st_zero, BPF_ST_MEM(BPF_DW, BPF_REG_FP, -8, 0))
: __clobber_common);
}
> + /* fp-16 is const zero register */
> + "r0 = 0;"
> + "*(u64 *)(r10 -16) = r0;"
> +
> + /* load single U8 from non-aligned STACK_ZERO slot */
> + "r1 = %[single_byte_buf];"
> + "r2 = *(u8 *)(r10 -1);"
> + "r1 += r2;" /* this should be fine */
Question: the comment suggests that adding something other than
zero would be an error, however error would only be
reported if *r1 is attempted, maybe add such access?
E.g. "*(u8 *)(r1 + 0) = r2;"?
[...]
next prev parent reply other threads:[~2023-11-21 16:20 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-21 0:22 [PATCH v2 bpf-next 00/10] Complete BPF verifier precision tracking support for register spills Andrii Nakryiko
2023-11-21 0:22 ` [PATCH v2 bpf-next 01/10] bpf: support non-r10 register spill/fill to/from stack in precision tracking Andrii Nakryiko
2023-11-21 0:22 ` [PATCH v2 bpf-next 02/10] selftests/bpf: add stack access precision test Andrii Nakryiko
2023-11-21 0:42 ` Eduard Zingerman
2023-11-21 0:22 ` [PATCH v2 bpf-next 03/10] bpf: fix check for attempt to corrupt spilled pointer Andrii Nakryiko
2023-11-21 0:22 ` [PATCH v2 bpf-next 04/10] bpf: preserve STACK_ZERO slots on partial reg spills Andrii Nakryiko
2023-11-21 0:22 ` [PATCH v2 bpf-next 05/10] selftests/bpf: validate STACK_ZERO is preserved on subreg spill Andrii Nakryiko
2023-11-21 0:55 ` Eduard Zingerman
2023-11-21 0:22 ` [PATCH v2 bpf-next 06/10] bpf: preserve constant zero when doing partial register restore Andrii Nakryiko
2023-11-21 16:20 ` Eduard Zingerman
2023-11-21 18:14 ` Andrii Nakryiko
2023-11-21 20:22 ` Eduard Zingerman
2023-11-21 0:22 ` [PATCH v2 bpf-next 07/10] selftests/bpf: validate zero preservation for sub-slot loads Andrii Nakryiko
2023-11-21 16:20 ` Eduard Zingerman [this message]
2023-11-21 18:15 ` Andrii Nakryiko
2023-11-21 0:22 ` [PATCH v2 bpf-next 08/10] bpf: track aligned STACK_ZERO cases as imprecise spilled registers Andrii Nakryiko
2023-11-21 20:38 ` Alexei Starovoitov
2023-11-21 22:01 ` Andrii Nakryiko
2023-11-21 0:22 ` [PATCH v2 bpf-next 09/10] selftests/bpf: validate precision logic in partial_stack_load_preserves_zeros Andrii Nakryiko
2023-11-21 16:20 ` Eduard Zingerman
2023-11-21 0:22 ` [PATCH v2 bpf-next 10/10] bpf: use common instruction history across all states Andrii Nakryiko
2023-11-21 16:20 ` Eduard Zingerman
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