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 <[email protected]> CC: Peter Maydell <[email protected]> CC: Paolo Bonzini <[email protected]> Reported-by: Jann Horn <[email protected]> Signed-off-by: Pranith Kumar <[email protected]> Message-Id: <[email protected]> Signed-off-by: Paolo Bonzini <[email protected]>
itfvck · Mar 24, 2017 · 30663fd · 30663fd
1 parent 7140778
commit 30663fd
Showing 1 changed file with 7 additions and 0 deletions.
diff --git 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.  */