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Thu, 03 Sep 2026 06:34:44 -0700 (PDT) Received: from DESKTOP-NFZVUTU.localdomain ([176.240.169.64]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49cee60bae6sm88131755e9.9.2026.09.03.06.34.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Sep 2026 06:34:44 -0700 (PDT) From: Utku Erol To: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com Cc: martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, qmo@kernel.org, emil@etsalapatis.com, ihor.solodrai@linux.dev, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Utku Erol Subject: [PATCH] bpf: disasm: guard print_bpf_insn against BPF_MEMSX | BPF_DW Date: Thu, 3 Sep 2026 16:34:34 +0300 Message-Id: <20260903133434.17860-1-utkuerol71@gmail.com> X-Mailer: git-send-email 2.34.1 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" print_bpf_insn() renders a BPF_LDX by indexing one of two size tables with BPF_SIZE(insn->code) >> 3. For BPF_MEMSX it uses bpf_ldsx_string[], which has only three entries (W/H/B) because a sign-extended doubleword load is not a valid instruction. The LDX branch checks only that the mode is BPF_MEM or BPF_MEMSX; it never rejects BPF_MEMSX | BPF_DW. For that opcode BPF_SIZE(code) >> 3 =3D=3D BPF_DW >> 3 =3D=3D 3, one element past the end o= f the 3-entry array: UBSAN: array-index-out-of-bounds: index 3 out of range for 'char *[3]' KASAN: global-out-of-bounds: 8-byte read in print_bpf_insn The out-of-bounds slot is then dereferenced as %s. The disassembler is expected to run on unvalidated instructions. Since commit b9c5d822f677 ("bpf: Add source and instruction diagnostic context") the diagnostics facility disassembles instruction context from check_subprogs(), before check_insn_fields() has rejected the opcode, so a raw BPF_MEMSX | BPF_DW insn reaches print_bpf_insn on the ordinary bpf_prog_load() path whenever a verifier log is requested (log_level >=3D 1= ). Reject the impossible size the same way the branch already rejects an unexpected mode, keeping the disassembler total for any opcode. Fixes: b9c5d822f677 ("bpf: Add source and instruction diagnostic context") Signed-off-by: Utku Erol --- kernel/bpf/disasm.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c index 50b3ca5149a0..70c2b281cfe9 100644 --- a/kernel/bpf/disasm.c +++ b/kernel/bpf/disasm.c @@ -299,6 +299,10 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs, verbose(cbs->private_data, "BUG_ldx_%02x", insn->code); return; } + if (BPF_MODE(insn->code) =3D=3D BPF_MEMSX && BPF_SIZE(insn->code) =3D=3D= BPF_DW) { + verbose(cbs->private_data, "BUG_ldsx_%02x", insn->code); + return; + } verbose(cbs->private_data, "(%02x) r%d =3D *(%s *)(r%d %+d)", insn->code, insn->dst_reg, BPF_MODE(insn->code) =3D=3D BPF_MEM ? --=20 2.34.1