linux-kernel - Re: [PATCH 2/3] livepatch: Allow user to specify functions to search for on a stack

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Message-ID: <YZd5yeql//37xSuw@hirez.programming.kicks-ass.net>
Date:   Fri, 19 Nov 2021 11:17:45 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     jpoimboe@...hat.com, jikos@...nel.org, pmladek@...e.com,
        joe.lawrence@...hat.com, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org, shuah@...nel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 2/3] livepatch: Allow user to specify functions to search
 for on a stack

On Fri, Nov 19, 2021 at 10:03:26AM +0100, Miroslav Benes wrote:
> livepatch's consistency model requires that no live patched function
> must be found on any task's stack during a transition process after a
> live patch is applied. It is achieved by walking through stacks of all
> blocked tasks.
> 
> The user might also want to define more functions to search for without
> them being patched at all. It may either help with preparing a live
> patch, which would otherwise require additional touches to achieve the
> consistency, or it can be used to overcome deficiencies the stack
> checking inherently has. For example, GCC may optimize a function so
> that a part of it is moved to a different section and the function would
> jump to it. This child function would not be found on a stack in this
> case, but it may be important to search for it so that, again, the
> consistency is achieved.
> 
> Allow the user to specify such functions on klp_object level.

Ok, so this relies on the patch generator to DTRT but then it should
work.

Thanks!