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Wed, 17 Dec 2025 01:55:07 -0800 (PST) From: Menglong Dong X-Google-Original-From: Menglong Dong To: ast@kernel.org, andrii@kernel.org Cc: davem@davemloft.net, dsahern@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH bpf-next v4 2/9] bpf: use last 8-bits for the nr_args in trampoline Date: Wed, 17 Dec 2025 17:54:38 +0800 Message-ID: <20251217095445.218428-3-dongml2@chinatelecom.cn> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251217095445.218428-1-dongml2@chinatelecom.cn> References: <20251217095445.218428-1-dongml2@chinatelecom.cn> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit For now, ctx[-1] is used to store the nr_args in the trampoline. However, 1-byte is enough to store such information. Therefor, we use only the last byts of ctx[-1] to store the nr_args, and reverve the rest for other usages. Signed-off-by: Menglong Dong --- kernel/bpf/verifier.c | 35 +++++++++++++++++++---------------- kernel/trace/bpf_trace.c | 4 ++-- 2 files changed, 21 insertions(+), 18 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d399bfd2413f..96753833c090 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -23275,15 +23275,16 @@ static int do_misc_fixups(struct bpf_verifier_env *env) insn->imm == BPF_FUNC_get_func_arg) { /* Load nr_args from ctx - 8 */ insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8); - insn_buf[1] = BPF_JMP32_REG(BPF_JGE, BPF_REG_2, BPF_REG_0, 6); - insn_buf[2] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_2, 3); - insn_buf[3] = BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_1); - insn_buf[4] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_2, 0); - insn_buf[5] = BPF_STX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, 0); - insn_buf[6] = BPF_MOV64_IMM(BPF_REG_0, 0); - insn_buf[7] = BPF_JMP_A(1); - insn_buf[8] = BPF_MOV64_IMM(BPF_REG_0, -EINVAL); - cnt = 9; + insn_buf[1] = BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xFF); + insn_buf[2] = BPF_JMP32_REG(BPF_JGE, BPF_REG_2, BPF_REG_0, 6); + insn_buf[3] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_2, 3); + insn_buf[4] = BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_1); + insn_buf[5] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_2, 0); + insn_buf[6] = BPF_STX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, 0); + insn_buf[7] = BPF_MOV64_IMM(BPF_REG_0, 0); + insn_buf[8] = BPF_JMP_A(1); + insn_buf[9] = BPF_MOV64_IMM(BPF_REG_0, -EINVAL); + cnt = 10; new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt); if (!new_prog) @@ -23303,12 +23304,13 @@ static int do_misc_fixups(struct bpf_verifier_env *env) eatype == BPF_MODIFY_RETURN) { /* Load nr_args from ctx - 8 */ insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8); - insn_buf[1] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_0, 3); - insn_buf[2] = BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_1); - insn_buf[3] = BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, 0); - insn_buf[4] = BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0); - insn_buf[5] = BPF_MOV64_IMM(BPF_REG_0, 0); - cnt = 6; + insn_buf[1] = BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xFF); + insn_buf[2] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_0, 3); + insn_buf[3] = BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_1); + insn_buf[4] = BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, 0); + insn_buf[5] = BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0); + insn_buf[6] = BPF_MOV64_IMM(BPF_REG_0, 0); + cnt = 7; } else { insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, -EOPNOTSUPP); cnt = 1; @@ -23329,8 +23331,9 @@ static int do_misc_fixups(struct bpf_verifier_env *env) insn->imm == BPF_FUNC_get_func_arg_cnt) { /* Load nr_args from ctx - 8 */ insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8); + insn_buf[1] = BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xFF); - new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, 1); + new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, 2); if (!new_prog) return -ENOMEM; diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index d57727abaade..10c9992d2745 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -1194,7 +1194,7 @@ const struct bpf_func_proto bpf_get_branch_snapshot_proto = { BPF_CALL_3(get_func_arg, void *, ctx, u32, n, u64 *, value) { /* This helper call is inlined by verifier. */ - u64 nr_args = ((u64 *)ctx)[-1]; + u64 nr_args = ((u64 *)ctx)[-1] & 0xFF; if ((u64) n >= nr_args) return -EINVAL; @@ -1214,7 +1214,7 @@ static const struct bpf_func_proto bpf_get_func_arg_proto = { BPF_CALL_2(get_func_ret, void *, ctx, u64 *, value) { /* This helper call is inlined by verifier. */ - u64 nr_args = ((u64 *)ctx)[-1]; + u64 nr_args = ((u64 *)ctx)[-1] & 0xFF; *value = ((u64 *)ctx)[nr_args]; return 0; -- 2.52.0