linux-kernel - Re: [PATCH 01/21] objtool: Fix seg fault in BT

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Date:   Thu, 14 Jan 2021 14:04:01 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com, Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH 01/21] objtool: Fix seg fault in BT_FUNC() with fake jump

On Thu, Jan 14, 2021 at 01:39:57PM -0600, Josh Poimboeuf wrote:
> Objtool appends a temporary fake jump at the end of alternative
> replacement instructions.  If the replacement code is empty -- resulting
> in patched nops -- the fake jump doesn't have a section.  When running
> objtool with '--backtrace', the fake jump's missing section can cause
> BT_FUNC() to trigger a seg fault when the NULL insn->sec is passed to
> offstr().
> 
> Fix it by ensuring fake jumps always have a section.
> 
> Fixes: 7697eee3ddd7 ("objtool: Add --backtrace support")
> Reported-by: Sami Tolvanen <samitolvanen@...gle.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>

This patch will probably end up getting dropped because fake jumps are
going away \o/

-- 
Josh