linux-kernel - Re: [PATCH] fs: export anon_inode_make_secure

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Message-ID: <20250623142836.GT1613200@noisy.programming.kicks-ass.net>
Date: Mon, 23 Jun 2025 16:28:36 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Christoph Hellwig <hch@...radead.org>,
	Christian Brauner <brauner@...nel.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Mike Rapoport <rppt@...nel.org>, Shivank Garg <shivankg@....com>,
	david@...hat.com, akpm@...ux-foundation.org, paul@...l-moore.com,
	viro@...iv.linux.org.uk, willy@...radead.org, pbonzini@...hat.com,
	tabba@...gle.com, afranji@...gle.com, ackerleytng@...gle.com,
	jack@...e.cz, cgzones@...glemail.com, ira.weiny@...el.com,
	roypat@...zon.co.uk, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH] fs: export anon_inode_make_secure_inode() and fix
 secretmem LSM bypass

On Mon, Jun 23, 2025 at 04:21:15PM +0200, Vlastimil Babka wrote:
> On 6/23/25 16:01, Christoph Hellwig wrote:
> > On Mon, Jun 23, 2025 at 07:00:39AM -0700, Christoph Hellwig wrote:
> >> On Mon, Jun 23, 2025 at 12:16:27PM +0200, Christian Brauner wrote:
> >> > I'm more than happy to switch a bunch of our exports so that we only
> >> > allow them for specific modules. But for that we also need
> >> > EXPOR_SYMBOL_FOR_MODULES() so we can switch our non-gpl versions.
> >> 
> >> Huh?  Any export for a specific in-tree module (or set thereof) is
> >> by definition internals and an _GPL export if perfectly fine and
> >> expected.
> 
> Peterz tells me EXPORT_SYMBOL_GPL_FOR_MODULES() is not limited to in-tree
> modules, so external module with GPL and matching name can import.
> 
> But if we're targetting in-tree stuff like kvm, we don't need to provide a
> non-GPL variant I think?

So the purpose was to limit specific symbols to known in-tree module
users (hence GPL only).

Eg. KVM; x86 exports a fair amount of low level stuff just because KVM.
Nobody else should be touching those symbols.

If you have a pile of symbols for !GPL / out-of-tree consumers, it
doesn't really make sense to limit the export to a named set of modules,
does it?

So yes, nothing limits things to in-tree modules per-se. The
infrastructure only really cares about module names (and implicitly
trusts the OS to not overwrite existing kernel modules etc.). So you
could add an out-of-tree module name to the list (or have an out-of-free
module have a name that matches a glob; "kvm-vmware" would match "kvm-*"
for example).

But that is very much beyond the intention of things.