linux-kernel - Re: [PATCH 0/7] livepatch,module: Remove .klp.arch and module_disable

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Message-ID: <10594420-de7b-bfab-d3cd-1e73d2f20af2@redhat.com>
Date:   Tue, 14 Apr 2020 21:37:53 -0400
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Jessica Yu <jeyu@...nel.org>
Subject: Re: [PATCH 0/7] livepatch,module: Remove .klp.arch and
 module_disable_ro()

On 4/14/20 9:31 PM, Josh Poimboeuf wrote:
> On Tue, Apr 14, 2020 at 08:57:15PM -0400, Joe Lawrence wrote:
>> On 4/14/20 12:28 PM, Josh Poimboeuf wrote:
>>> Better late than never, these patches add simplifications and
>>> improvements for some issues Peter found six months ago, as part of his
>>> non-writable text code (W^X) cleanups.
>>>
>>> Highlights:
>>>
>>> - Remove the livepatch arch-specific .klp.arch sections, which were used
>>>     to do paravirt patching and alternatives patching for livepatch
>>>     replacement code.
>>>
>>> - Add support for jump labels in patched code.
>>
>> Re: jump labels and late-module patching support...
>>
>> Is there still an issue of a non-exported static key defined in a
>> to-be-patched module referenced and resolved via klp-relocation when the
>> livepatch module is loaded first?  (Basically the same case I asked Petr
>> about in his split livepatch module PoC. [1])
>>
>> Or should we declare this an invalid klp-relocation use case and force the
>> livepatch author to use static_key_enabled()?
>>
>> [1] https://lore.kernel.org/lkml/20200407205740.GA17061@redhat.com/
> 
> Right, if the static key lives in a module, then it's still not possible
> for a jump label to use it.  I added a check in kpatch-build to block
> that case and suggest static_key_enabled() instead.
> 

Ok good.  I didn't see a negative test case for this, so I wanted to 
make sure that kpatch-build wouldn't accidentally create unsupported 
klp-relocations for them.  I'll try to review those changes over on 
github tomorrow.

-- Joe