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From: Yonghong Song <yhs@fb.com>
To: <bpf@vger.kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>, <kernel-team@fb.com>,
	Dave Marchevsky <davemarchevsky@fb.com>
Subject: [PATCH bpf-next v4 03/18] libbpf: Fix an error in 64bit relocation value computation
Date: Thu, 2 Jun 2022 18:59:10 -0700	[thread overview]
Message-ID: <20220603015910.1188721-1-yhs@fb.com> (raw)
In-Reply-To: <20220603015855.1187538-1-yhs@fb.com>

Currently, the 64bit relocation value in the instruction
is computed as follows:
  __u64 imm = insn[0].imm + ((__u64)insn[1].imm << 32)

Suppose insn[0].imm = -1 (0xffffffff) and insn[1].imm = 1.
With the above computation, insn[0].imm will first sign-extend
to 64bit -1 (0xffffffffFFFFFFFF) and then add 0x1FFFFFFFF,
producing incorrect value 0xFFFFFFFF. The correct value
should be 0x1FFFFFFFF.

Changing insn[0].imm to __u32 first will prevent 64bit sign
extension and fix the issue. Merging high and low 32bit values
also changed from '+' to '|' to be consistent with other
similar occurences in kernel and libbpf.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 tools/lib/bpf/relo_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/relo_core.c b/tools/lib/bpf/relo_core.c
index 0dce5644877b..073a54ed7432 100644
--- a/tools/lib/bpf/relo_core.c
+++ b/tools/lib/bpf/relo_core.c
@@ -1027,7 +1027,7 @@ int bpf_core_patch_insn(const char *prog_name, struct bpf_insn *insn,
 			return -EINVAL;
 		}
 
-		imm = insn[0].imm + ((__u64)insn[1].imm << 32);
+		imm = (__u32)insn[0].imm | ((__u64)insn[1].imm << 32);
 		if (res->validate && imm != orig_val) {
 			pr_warn("prog '%s': relo #%d: unexpected insn #%d (LDIMM64) value: got %llu, exp %llu -> %llu\n",
 				prog_name, relo_idx,
-- 
2.30.2


  parent reply	other threads:[~2022-06-03  1:59 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-03  1:58 [PATCH bpf-next v4 00/18] bpf: Add 64bit enum value support Yonghong Song
2022-06-03  1:59 ` [PATCH bpf-next v4 01/18] bpf: Add btf enum64 support Yonghong Song
2022-06-03  1:59 ` [PATCH bpf-next v4 02/18] libbpf: Permit 64bit relocation value Yonghong Song
2022-06-03  1:59 ` Yonghong Song [this message]
2022-06-03  1:59 ` [PATCH bpf-next v4 04/18] libbpf: Refactor btf__add_enum() for future code sharing Yonghong Song
2022-06-03  1:59 ` [PATCH bpf-next v4 05/18] libbpf: Add enum64 parsing and new enum64 public API Yonghong Song
2022-06-03  1:59 ` [PATCH bpf-next v4 06/18] libbpf: Add enum64 deduplication support Yonghong Song
2022-06-03 21:44   ` Andrii Nakryiko
2022-06-03  1:59 ` [PATCH bpf-next v4 07/18] libbpf: Add enum64 support for btf_dump Yonghong Song
2022-06-03 21:46   ` Andrii Nakryiko
2022-06-03  1:59 ` [PATCH bpf-next v4 08/18] libbpf: Add enum64 sanitization Yonghong Song
2022-06-03  1:59 ` [PATCH bpf-next v4 09/18] libbpf: Add enum64 support for bpf linking Yonghong Song
2022-06-03  1:59 ` [PATCH bpf-next v4 10/18] libbpf: Add enum64 relocation support Yonghong Song
2022-06-03 21:49   ` Andrii Nakryiko
2022-06-03  1:59 ` [PATCH bpf-next v4 11/18] bpftool: Add btf enum64 support Yonghong Song
2022-06-03  1:59 ` [PATCH bpf-next v4 12/18] selftests/bpf: Fix selftests failure Yonghong Song
2022-06-03  2:00 ` [PATCH bpf-next v4 13/18] selftests/bpf: Test new enum kflag and enum64 API functions Yonghong Song
2022-06-03  2:00 ` [PATCH bpf-next v4 14/18] selftests/bpf: Add BTF_KIND_ENUM64 unit tests Yonghong Song
2022-06-03  2:00 ` [PATCH bpf-next v4 15/18] selftests/bpf: Test BTF_KIND_ENUM64 for deduplication Yonghong Song
2022-06-03  2:00 ` [PATCH bpf-next v4 16/18] selftests/bpf: Add a test for enum64 value relocations Yonghong Song
2022-06-03 15:14   ` Alexei Starovoitov
2022-06-03 20:22     ` Andrii Nakryiko
2022-06-03 20:24       ` Andrii Nakryiko
2022-06-04  2:51     ` Yonghong Song
2022-06-04  9:34       ` Alexei Starovoitov
2022-06-03  2:00 ` [PATCH bpf-next v4 17/18] selftests/bpf: Clarify llvm dependency with possible selftest failures Yonghong Song
2022-06-03  2:00 ` [PATCH bpf-next v4 18/18] docs/bpf: Update documentation for BTF_KIND_ENUM64 support Yonghong Song

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