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Re: [Qemu-devel] [PATCH] tcg/i386: Check the size of instruction being t
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] tcg/i386: Check the size of instruction being translated |
Date: |
Fri, 24 Mar 2017 11:49:52 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 |
Queued, thanks.
Paolo
On 23/03/2017 18:58, Pranith Kumar wrote:
> Sending again since I messed by pbonzini's email.
>
> 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
>
> CC: Richard Henderson <address@hidden>
> CC: Peter Maydell <address@hidden>
> CC: Paolo Bonzini <address@hidden>
> Reported-by: Jann Horn <address@hidden>
> Signed-off-by: Pranith Kumar <address@hidden>
> ---
> 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. */
>