linux-kernel - Re: [PATCH] x86/kprobes: Fix 1 byte conditional jump target

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Message-Id: <5DFB6E19-210E-4EA8-8D71-66FF4A787942@gmail.com>
Date:   Sun, 5 Feb 2023 09:49:56 +0200
From:   Nadav Amit <nadav.amit@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        X86 ML <x86@...nel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] x86/kprobes: Fix 1 byte conditional jump target



> On Feb 4, 2023, at 11:08 PM, Nadav Amit <nadav.amit@...il.com> wrote:
> 
> From: Nadav Amit <namit@...are.com>
> 
> Commit 3bc753c06dd0 ("kbuild: treat char as always unsigned") broke
> kprobes.  Setting a probe-point on 1 byte conditional jump can cause the
> kernel to crash, as the branch target is not sign extended.
> 
> Fix by using s8 instead of char and use immediate.value instead of
> immediate.bytes for consistency.

I guess I forgot to put a “Fixes” tag, since it is still not a real
regression. (The bug was introduced in 6.2).

Still, this fix should not fall between the cracks… Please let me know
whether v2 is needed with a “fixes” tag.