From: Steven Rostedt <rostedt@goodmis.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
Ivan Babrou <ivan@cloudflare.com>,
Peter Zijlstra <peterz@infradead.org>,
stable@vger.kernel.org
Subject: Re: [PATCH 1/2] x86/unwind/orc: Disable KASAN checking in the ORC unwinder, part 2
Date: Fri, 5 Feb 2021 09:51:11 -0500 [thread overview]
Message-ID: <20210205095111.2dba8515@gandalf.local.home> (raw)
In-Reply-To: <9583327904ebbbeda399eca9c56d6c7085ac20fe.1612534649.git.jpoimboe@redhat.com>
On Fri, 5 Feb 2021 08:24:02 -0600
Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> KASAN reserves "redzone" areas between stack frames in order to detect
> stack overruns. A read or write to such an area triggers a KASAN
> "stack-out-of-bounds" BUG.
>
> Normally, the ORC unwinder stays in-bounds and doesn't access the
> redzone. But sometimes it can't find ORC metadata for a given
> instruction. This can happen for code which is missing ORC metadata, or
> for generated code. In such cases, the unwinder attempts to fall back
> to frame pointers, as a best-effort type thing.
>
> This fallback often works, but when it doesn't, the unwinder can get
> confused and go off into the weeds into the KASAN redzone, triggering
> the aforementioned KASAN BUG.
>
> But in this case, the unwinder's confusion is actually harmless and
> working as designed. It already has checks in place to prevent
> off-stack accesses, but those checks get short-circuited by the KASAN
> BUG. And a BUG is a lot more disruptive than a harmless unwinder
> warning.
>
> Disable the KASAN checks by using READ_ONCE_NOCHECK() for all stack
> accesses. This finishes the job started by commit 881125bfe65b
> ("x86/unwind: Disable KASAN checking in the ORC unwinder"), which only
> partially fixed the issue.
>
> Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
> Reported-by: Ivan Babrou <ivan@cloudflare.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
-- Steve
next prev parent reply other threads:[~2021-02-05 22:52 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-05 14:24 [PATCH 0/2] x86/unwind/orc: Handle missing ORC data better Josh Poimboeuf
2021-02-05 14:24 ` [PATCH 1/2] x86/unwind/orc: Disable KASAN checking in the ORC unwinder, part 2 Josh Poimboeuf
2021-02-05 14:51 ` Steven Rostedt [this message]
2021-02-05 18:27 ` Ivan Babrou
2021-03-04 8:51 ` [tip: x86/urgent] " tip-bot2 for Josh Poimboeuf
2021-03-06 10:44 ` tip-bot2 for Josh Poimboeuf
2021-03-06 12:18 ` tip-bot2 for Josh Poimboeuf
2021-02-05 14:24 ` [PATCH 2/2] x86/unwind/orc: Silence warnings caused by missing ORC data Josh Poimboeuf
2021-02-08 19:56 ` Josh Poimboeuf
2021-02-08 20:00 ` Ivan Babrou
2021-02-24 14:52 ` Peter Zijlstra
2021-02-24 15:18 ` Josh Poimboeuf
2021-02-24 18:07 ` Peter Zijlstra
2021-02-24 18:12 ` Josh Poimboeuf
2021-03-04 8:51 ` [tip: x86/urgent] " tip-bot2 for Josh Poimboeuf
2021-03-06 10:44 ` tip-bot2 for Josh Poimboeuf
2021-03-06 12:18 ` tip-bot2 for Josh Poimboeuf
2021-02-24 12:02 ` [PATCH 0/2] x86/unwind/orc: Handle missing ORC data better Miroslav Benes
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