linux-kernel - Re: [PATCH 1/2] arm64: Implement arch_stack_walk

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <iajk7zuxy7fun7f7sv52ydhq7siqub3ec2lmguomdd3fhdw4s2@cwyfihj3gvpn>
Date: Tue, 18 Mar 2025 11:45:40 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Song Liu <song@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-toolchains@...r.kernel.org, live-patching@...r.kernel.org, indu.bhagat@...cle.com, 
	puranjay@...nel.org, wnliu@...gle.com, irogers@...gle.com, joe.lawrence@...hat.com, 
	mark.rutland@....com, peterz@...radead.org, roman.gushchin@...ux.dev, 
	rostedt@...dmis.org, will@...nel.org, kernel-team@...a.com
Subject: Re: [PATCH 1/2] arm64: Implement arch_stack_walk_reliable

On Fri, Mar 07, 2025 at 05:27:41PM -0800, Song Liu wrote:
> With proper exception boundary detection, it is possible to implment
> arch_stack_walk_reliable without sframe.
> 
> Note that, arch_stack_walk_reliable does not guarantee getting reliable
> stack in all scenarios. Instead, it can reliably detect when the stack
> trace is not reliable, which is enough to provide reliable livepatching.
> 
> This version has been inspired by Weinan Liu's patch [1].
> 
> [1] https://lore.kernel.org/live-patching/20250127213310.2496133-7-wnliu@google.com/
> Signed-off-by: Song Liu <song@...nel.org>

This looks incomplete.  The reliable unwinder needs to be extra
paranoid.  There are several already-checked-for errors in the unwinder
that don't actually set the unreliable bit.

There are likely other failure modes it should also be checking for.
For example I don't see where it confirms that the unwind completed to
the end of the stack (which is typically at a certain offset).

See for example all the error conditions in the x86 version of
arch_stack_walk_reliable() and in arch/x86/kernel/unwind_frame.c.

-- 
Josh