From 37e5c4f4d2856290b1c56e573ced91dcd88db8ec Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Thu, 20 Aug 2026 04:20:18 +0200 Subject: [PATCH] bpf: Reject invalid LDSX instruction in disassembly The signed-load mnemonic table has entries for byte, half-word, and word loads because BPF_MEMSX does not support double-word loads. A BPF_MEMSX | BPF_DW instruction nevertheless selects index 3, past the end of this table. Program Structure diagnostics can disassemble a malformed instruction before check_and_resolve_insns() rejects its opcode. Placing the invalid signed double-word load at the end of a program therefore triggers an out-of-bounds access while reporting subprogram fallthrough. Treat signed double-word loads as invalid in the disassembler and use the existing BUG_ldx fallback instead. Fixes: a8f427835394 ("bpf: Report Program Structure CFG errors") Reported-by: syzbot+3544d9b2a9206be8ba37@syzkaller.appspotmail.com Signed-off-by: Kumar Kartikeya Dwivedi Signed-off-by: Daniel Borkmann Reviewed-by: Jiayuan Chen Link: https://lore.kernel.org/bpf/20260820022020.3450479-2-memxor@gmail.com --- kernel/bpf/disasm.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c index 50b3ca5149a0..b1a3fbe3fda5 100644 --- a/kernel/bpf/disasm.c +++ b/kernel/bpf/disasm.c @@ -295,7 +295,8 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs, verbose(cbs->private_data, "BUG_st_%02x", insn->code); } } else if (class == BPF_LDX) { - if (BPF_MODE(insn->code) != BPF_MEM && BPF_MODE(insn->code) != BPF_MEMSX) { + if ((BPF_MODE(insn->code) != BPF_MEM && BPF_MODE(insn->code) != BPF_MEMSX) || + (BPF_MODE(insn->code) == BPF_MEMSX && BPF_SIZE(insn->code) == BPF_DW)) { verbose(cbs->private_data, "BUG_ldx_%02x", insn->code); return; }