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From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
	rostedt@goodmis.org, mhiramat@kernel.org, bristot@redhat.com,
	jbaron@akamai.com, torvalds@linux-foundation.org,
	tglx@linutronix.de, mingo@kernel.org, namit@vmware.com,
	hpa@zytor.com, luto@kernel.org, ard.biesheuvel@linaro.org,
	jeyu@kernel.org, live-patching@vger.kernel.org
Subject: Re: [PATCH v4 15/16] module: Move where we mark modules RO,X
Date: Thu, 24 Oct 2019 15:16:34 +0200
Message-ID: <20191024131634.GC4131@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20191023170025.f34g3vxaqr4f5gqh@treble>

On Wed, Oct 23, 2019 at 12:00:25PM -0500, Josh Poimboeuf wrote:

> > This then raises a number of questions:
> > 
> >  1) why is that RELA (that obviously does not depend on any module)
> >     applied so late?
> 
> Good question.  The 'pv_ops' symbol is exported by the core kernel, so I
> can't see any reason why we'd need to apply that rela late.  In theory,
> kpatch-build isn't supposed to convert that to a klp rela.  Maybe
> something went wrong in the patch creation code.
> 
> I'm also questioning why we even need to apply the parainstructions
> section late.  Maybe we can remove that apply_paravirt() call
> altogether, along with .klp.arch.parainstruction sections.
> 
> I'll need to look into it...

Right, that really should be able to run early. Esp. after commit

  11e86dc7f274 ("x86/paravirt: Detect over-sized patching bugs in paravirt_patch_call()")

paravirt patching is unconditional. We _never_ run with the indirect
call except very early boot, but modules should have them patched way
before their init section runs.

We rely on this for spectre-v2 and friends.

> >  3) Is there ever a possible module-dependent RELA to a paravirt /
> >     alternative site?
> 
> Good question...

> > Then for 3) we only have alternatives left, and I _think_ it unlikely to
> > be the case, but I'll have to have a hard look at that.
> 
> I'm not sure about alternatives, but maybe we can enforce such
> limitations with tooling and/or kernel checks.

Right, so on IRC you implied you might have some additional details on
how alternatives were affected; did you manage to dig that up?

  reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20191018073525.768931536@infradead.org>
     [not found] ` <20191018074634.801435443@infradead.org>
     [not found]   ` <20191021135312.jbbxsuipxldocdjk@treble>
     [not found]     ` <20191021141402.GI1817@hirez.programming.kicks-ass.net>
     [not found]       ` <20191023114835.GT1817@hirez.programming.kicks-ass.net>
2019-10-23 17:00         ` Josh Poimboeuf
2019-10-24 13:16           ` Peter Zijlstra [this message]
2019-10-25  6:44             ` Petr Mladek
2019-10-25  8:43               ` Peter Zijlstra
2019-10-25 10:06                 ` Peter Zijlstra
2019-10-25 13:50                   ` Josh Poimboeuf
2019-10-26  1:17                   ` Josh Poimboeuf
2019-10-28 10:07                     ` Peter Zijlstra
2019-10-28 10:43                     ` Peter Zijlstra
2019-10-25  9:16               ` Peter Zijlstra

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