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Thu, 15 Jan 2026 03:23:21 -0800 (PST) From: Menglong Dong X-Google-Original-From: Menglong Dong To: ast@kernel.org, andrii@kernel.org Cc: 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, davem@davemloft.net, dsahern@kernel.org, tglx@linutronix.de, mingo@redhat.com, jiang.biao@linux.dev, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH bpf-next v10 02/12] bpf: use the least significant byte for the nr_args in trampoline Date: Thu, 15 Jan 2026 19:22:36 +0800 Message-ID: <20260115112246.221082-3-dongml2@chinatelecom.cn> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260115112246.221082-1-dongml2@chinatelecom.cn> References: <20260115112246.221082-1-dongml2@chinatelecom.cn> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" For now, ((u64 *)ctx)[-1] is used to store the nr_args in the trampoline. However, 1 byte is enough to store such information. Therefore, we use only the least significant byte of ((u64 *)ctx)[-1] to store the nr_args, and reserve the rest for other usages. Signed-off-by: Menglong Dong --- v10: - some adjustment to the subject and commit log to make the description more precise. v8: - fix the missed get_func_arg_cnt --- kernel/bpf/verifier.c | 35 +++++++++++++++++++---------------- kernel/trace/bpf_trace.c | 6 +++--- 2 files changed, 22 insertions(+), 19 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index db935eaddc2d..f7eec19df803 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -23319,15 +23319,16 @@ static int do_misc_fixups(struct bpf_verifier_env= *env) insn->imm =3D=3D BPF_FUNC_get_func_arg) { /* Load nr_args from ctx - 8 */ insn_buf[0] =3D BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8); - insn_buf[1] =3D BPF_JMP32_REG(BPF_JGE, BPF_REG_2, BPF_REG_0, 6); - insn_buf[2] =3D BPF_ALU64_IMM(BPF_LSH, BPF_REG_2, 3); - insn_buf[3] =3D BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_1); - insn_buf[4] =3D BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_2, 0); - insn_buf[5] =3D BPF_STX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, 0); - insn_buf[6] =3D BPF_MOV64_IMM(BPF_REG_0, 0); - insn_buf[7] =3D BPF_JMP_A(1); - insn_buf[8] =3D BPF_MOV64_IMM(BPF_REG_0, -EINVAL); - cnt =3D 9; + insn_buf[1] =3D BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xFF); + insn_buf[2] =3D BPF_JMP32_REG(BPF_JGE, BPF_REG_2, BPF_REG_0, 6); + insn_buf[3] =3D BPF_ALU64_IMM(BPF_LSH, BPF_REG_2, 3); + insn_buf[4] =3D BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_1); + insn_buf[5] =3D BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_2, 0); + insn_buf[6] =3D BPF_STX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, 0); + insn_buf[7] =3D BPF_MOV64_IMM(BPF_REG_0, 0); + insn_buf[8] =3D BPF_JMP_A(1); + insn_buf[9] =3D BPF_MOV64_IMM(BPF_REG_0, -EINVAL); + cnt =3D 10; =20 new_prog =3D bpf_patch_insn_data(env, i + delta, insn_buf, cnt); if (!new_prog) @@ -23347,12 +23348,13 @@ static int do_misc_fixups(struct bpf_verifier_env= *env) eatype =3D=3D BPF_MODIFY_RETURN) { /* Load nr_args from ctx - 8 */ insn_buf[0] =3D BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8); - insn_buf[1] =3D BPF_ALU64_IMM(BPF_LSH, BPF_REG_0, 3); - insn_buf[2] =3D BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_1); - insn_buf[3] =3D BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, 0); - insn_buf[4] =3D BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0); - insn_buf[5] =3D BPF_MOV64_IMM(BPF_REG_0, 0); - cnt =3D 6; + insn_buf[1] =3D BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xFF); + insn_buf[2] =3D BPF_ALU64_IMM(BPF_LSH, BPF_REG_0, 3); + insn_buf[3] =3D BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_1); + insn_buf[4] =3D BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, 0); + insn_buf[5] =3D BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0); + insn_buf[6] =3D BPF_MOV64_IMM(BPF_REG_0, 0); + cnt =3D 7; } else { insn_buf[0] =3D BPF_MOV64_IMM(BPF_REG_0, -EOPNOTSUPP); cnt =3D 1; @@ -23373,8 +23375,9 @@ static int do_misc_fixups(struct bpf_verifier_env *= env) insn->imm =3D=3D BPF_FUNC_get_func_arg_cnt) { /* Load nr_args from ctx - 8 */ insn_buf[0] =3D BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8); + insn_buf[1] =3D BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xFF); =20 - new_prog =3D bpf_patch_insn_data(env, i + delta, insn_buf, 1); + new_prog =3D bpf_patch_insn_data(env, i + delta, insn_buf, 2); if (!new_prog) return -ENOMEM; =20 diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 6e076485bf70..5f621f0403f8 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_p= roto =3D { BPF_CALL_3(get_func_arg, void *, ctx, u32, n, u64 *, value) { /* This helper call is inlined by verifier. */ - u64 nr_args =3D ((u64 *)ctx)[-1]; + u64 nr_args =3D ((u64 *)ctx)[-1] & 0xFF; =20 if ((u64) n >=3D nr_args) return -EINVAL; @@ -1214,7 +1214,7 @@ static const struct bpf_func_proto bpf_get_func_arg_p= roto =3D { BPF_CALL_2(get_func_ret, void *, ctx, u64 *, value) { /* This helper call is inlined by verifier. */ - u64 nr_args =3D ((u64 *)ctx)[-1]; + u64 nr_args =3D ((u64 *)ctx)[-1] & 0xFF; =20 *value =3D ((u64 *)ctx)[nr_args]; return 0; @@ -1231,7 +1231,7 @@ static const struct bpf_func_proto bpf_get_func_ret_p= roto =3D { BPF_CALL_1(get_func_arg_cnt, void *, ctx) { /* This helper call is inlined by verifier. */ - return ((u64 *)ctx)[-1]; + return ((u64 *)ctx)[-1] & 0xFF; } =20 static const struct bpf_func_proto bpf_get_func_arg_cnt_proto =3D { --=20 2.52.0