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

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Message-ID: <ZyosbEMNzMU6fOe_@infradead.org>
Date: Tue, 5 Nov 2024 06:32:12 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Christoph Hellwig <hch@...radead.org>, 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 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
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.