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

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Message-ID: <20241105145842.GH10375@noisy.programming.kicks-ass.net>
Date: Tue, 5 Nov 2024 15:58:42 +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 06:32:12AM -0800, Christoph Hellwig wrote:
> On Tue, Nov 05, 2024 at 03:27:20PM +0100, Peter Zijlstra wrote:
> > > I don't think that is the case at all.  The is a relatively small number
> > > of exported symbols that are called indirectly.  I'd much rather mark
> > > those explicitly.
> > 
> > I'm not claiming they have their address taken -- just saying that
> > traditionally this has always been a valid thing to do.
> > 
> > Anyway, I raised this point last time, and I think back then the
> > consensus was to explicitly mark those you should not be able to call.
> 
> Who came to that consensus?  There really is just a relatively well

The people who found that thread.

> 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.

I think the idea was that we add EXPORT_SYMBOL{,_GPL}_SEALED() and go
convert everything over to that.

Anyway, 0-day just informed me that this patch has a wee build issue :-/
That robot always waits until after you post to tell you.