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SubjectRe: Doubled "opcode != 0x9a" check
On Wed, 26 Jul 2017 21:55:34 +0200
Denys Vlasenko <vda.linux@googlemail.com> wrote:

> commit bd0b90676c30fe640e7ead919b3e38846ac88ab7
> Author: Masami Hiramatsu <mhiramat@kernel.org>
> Date: Wed Mar 29 13:56:56 2017 +0900
>
> kprobes/x86: Fix kprobe-booster not to boost far call instructions
>
> Fix the kprobe-booster not to boost far call instruction,
> because a call may store the address in the single-step
> execution buffer to the stack, which should be modified
> after single stepping.
>
> Currently, this instruction will be filtered as not
> boostable in resume_execution(), so this is not a
> critical issue.
> ... case 0x70:
> return 0; /* can't boost conditional jump */
> + case 0x90:
> + return opcode != 0x9a; /* can't boost call far */
> case 0xc0:
>
>
> Masami. You missed the fact that later, there is this:

Oops, right. Hmm, it should be reverted.
Ingo, could you revert this commit?

Thank you!

>
> default:
> /* segment override prefixes are boostable */
> if (opcode == 0x26 || opcode == 0x36 || opcode == 0x3e)
> goto retry; /* prefixes */
> /* CS override prefix and call are not boostable */
> return (opcode != 0x2e && opcode != 0x9a);
> ^^^^^^^^^^^^^^^^


--
Masami Hiramatsu <mhiramat@kernel.org>

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