From 31b977ab3ec9061614c2605212565e2d0640cd1b Mon Sep 17 00:00:00 2001 From: Pranith Kumar Date: Fri, 2 Mar 2018 14:19:28 -0500 Subject: [PATCH] tcg/i386: Check the size of instruction being translated This fixes the bug: 'user-to-root privesc inside VM via bad translation caching' reported by Jann Horn here: https://bugs.chromium.org/p/project-zero/issues/detail?id=1122 Backports commit 30663fd26c0307e414622c7a8607fbc04f92ec14 from qemu --- qemu/target/i386/translate.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/qemu/target/i386/translate.c b/qemu/target/i386/translate.c index c89503ed..cf98375f 100644 --- a/qemu/target/i386/translate.c +++ b/qemu/target/i386/translate.c @@ -5048,6 +5048,13 @@ static target_ulong disas_insn(CPUX86State *env, DisasContext *s, s->vex_l = 0; s->vex_v = 0; next_byte: + /* x86 has an upper limit of 15 bytes for an instruction. Since we + * do not want to decode and generate IR for an illegal + * instruction, the following check limits the instruction size to + * 25 bytes: 14 prefix + 1 opc + 6 (modrm+sib+ofs) + 4 imm */ + if (s->pc - pc_start > 14) { + goto illegal_op; + } b = cpu_ldub_code(env, s->pc); s->pc++; /* Collect prefixes. */