linux-kernel - Re: [PATCH 2/2] x86/retpoline,kprobes: Avoid treating rethunk as an indirect jump

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Message-ID: <20230705085857.GG462772@hirez.programming.kicks-ass.net>
Date:   Wed, 5 Jul 2023 10:58:57 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Petr Pavlu <petr.pavlu@...e.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mhiramat@...nel.org,
        samitolvanen@...gle.com, x86@...nel.org,
        linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86/retpoline,kprobes: Avoid treating rethunk as an
 indirect jump

On Wed, Jul 05, 2023 at 10:15:47AM +0200, Petr Pavlu wrote:
> Functions can_optimize() and insn_is_indirect_jump() consider jumps to
> the range [__indirect_thunk_start, __indirect_thunk_end] as indirect
> jumps and prevent use of optprobes in functions containing them.

Why ?!? I mean, doing an opt-probe of an indirect jump/call instruction
itself doesn't really make sense and I can see why you'd want to not do
that. But why disallow an opt-probe if there's one in the function as a
whole, but not the probe target?