linux-kernel - Re: [PATCH] x86/kprobes: Fix optprobe to detect padding int3 correctly

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Date:   Fri, 11 Dec 2020 11:39:15 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Adam Zabrocki <pi3@....com.pl>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Solar Designer <solar@...nwall.com>
Subject: Re: [PATCH] x86/kprobes: Fix optprobe to detect padding int3
 correctly

On Fri, Dec 11, 2020 at 04:04:17PM +0900, Masami Hiramatsu wrote:
> Fix optprobe to detect padding int3 correctly.
> 
> Since commit 7705dc855797 ("x86/vmlinux: Use INT3 instead of NOP
> for linker fill bytes") changed the padding bytes between functions
> from nop to int3, when optprobe decodes a target function it finds
> int3 and gives up the jump optimization.
> 
> Instead of giving up any int3 detection, this checks whether the
> rest of bytes to the end of the function are int3 or not. If all
> of those are int3, those come from the linker. In that case,
> optprobe continues jump optimization.
> 
> Fixes: 7705dc855797 ("x86/vmlinux: Use INT3 instead of NOP for linker fill bytes")
> Cc: stable@...r.kernel.org
> Reported-by: Adam Zabrocki <pi3@....com.pl>
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook