From 30663fd26c0307e414622c7a8607fbc04f92ec14 Mon Sep 17 00:00:00 2001 From: Pranith Kumar Date: Thu, 23 Mar 2017 13:58:51 -0400 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 Reviewed-by: Richard Henderson CC: Peter Maydell CC: Paolo Bonzini Reported-by: Jann Horn Signed-off-by: Pranith Kumar Message-Id: <20170323175851.14342-1-bobby.prani@gmail.com> Signed-off-by: Paolo Bonzini --- target/i386/translate.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/target/i386/translate.c b/target/i386/translate.c index 72c1b03a2a..1d1372fb43 100644 --- a/target/i386/translate.c +++ b/target/i386/translate.c @@ -4418,6 +4418,13 @@ 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. */