linux-kernel - Re: [PATCH v15 10/11] livepatch: Remove ordering (stacking) of the livepatches

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Message-ID: <alpine.LSU.2.21.1901101456150.15065@pobox.suse.cz>
Date:   Thu, 10 Jan 2019 14:56:31 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Petr Mladek <pmladek@...e.com>
cc:     Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v15 10/11] livepatch: Remove ordering (stacking) of the
 livepatches

On Wed, 9 Jan 2019, Petr Mladek wrote:

> The atomic replace and cumulative patches were introduced as a more secure
> way to handle dependent patches. They simplify the logic:
> 
>   + Any new cumulative patch is supposed to take over shadow variables
>     and changes made by callbacks from previous livepatches.
> 
>   + All replaced patches are discarded and the modules can be unloaded.
>     As a result, there is only one scenario when a cumulative livepatch
>     gets disabled.
> 
> The different handling of "normal" and cumulative patches might cause
> confusion. It would make sense to keep only one mode. On the other hand,
> it would be rude to enforce using the cumulative livepatches even for
> trivial and independent (hot) fixes.
> 
> However, the stack of patches is not really necessary any longer.
> The patch ordering was never clearly visible via the sysfs interface.
> Also the "normal" patches need a lot of caution anyway.
> 
> Note that the list of enabled patches is still necessary but the ordering
> is not longer enforced.
> 
> Otherwise, the code is ready to disable livepatches in an random order.
> Namely, klp_check_stack_func() always looks for the function from
> the livepatch that is being disabled. klp_func structures are just
> removed from the related func_stack. Finally, the ftrace handlers
> is removed only when the func_stack becomes empty.
> 
> Signed-off-by: Petr Mladek <pmladek@...e.com>

Acked-by: Miroslav Benes <mbenes@...e.cz>

Miroslav