linux-kernel - Re: [PATCH 1/8] x86,kcfi: Fix EXPORT

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Message-ID: <20241105161104.GK10375@noisy.programming.kicks-ass.net>
Date: Tue, 5 Nov 2024 17:11:04 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Christoph Hellwig <hch@...radead.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, alyssa.milburn@...el.com,
	scott.d.constable@...el.com, joao@...rdrivepizza.com,
	andrew.cooper3@...rix.com, jpoimboe@...nel.org,
	alexei.starovoitov@...il.com, ebiggers@...nel.org,
	samitolvanen@...gle.com, kees@...nel.org
Subject: Re: [PATCH 1/8] x86,kcfi: Fix EXPORT_SYMBOL vs kCFI

On Tue, Nov 05, 2024 at 04:47:40PM +0100, Peter Zijlstra wrote:
> On Tue, Nov 05, 2024 at 07:41:13AM -0800, Christoph Hellwig wrote:
> > On Tue, Nov 05, 2024 at 03:58:42PM +0100, Peter Zijlstra wrote:
> > > > bounded number of functions that are used as either default methods
> > > > or as ready made callbacks.  Everything else has no business being
> > > > called indirectly.  While disallowing this might be a bit of work,
> > > > I think it would be a great security improvement.
> > > 
> > > Well, we don't disagree. But since most of the EXPORT'ed functions are
> > > done in C, we need something that works there too.
> > 
> > Yes, absolutely.  In fact I doubt there are more than a handful of
> > assembly exports that are valid targets for indirect calls.
> 
> Yeah, I went overboard here. Let me tone it down a little.

OK, I removed a ton of them and fixed the build fallout. I've pushed it
out to the git tree mentioned somewhere, and will re-post in a few days.