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Date: Wed, 20 Mar 2024 15:47:34 +0000
From: Lee Jones <lee@kernel.org>
To: Michal Hocko <mhocko@suse.com>
Cc: cve@kernel.org, linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Felix Kuehling <felix.kuehling@amd.com>
Subject: Re: CVE-2024-26628: drm/amdkfd: Fix lock dependency warning
Message-ID: <20240320154734.GU1522089@google.com>
References: <2024030649-CVE-2024-26628-f6ce@gregkh>
 <Zerheyn-4rB5kySt@tiehlicka>
 <20240314110938.GM1522089@google.com>
 <ZfsBpal_29lihveI@tiehlicka>
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On Wed, 20 Mar 2024, Michal Hocko wrote:

> On Thu 14-03-24 11:09:38, Lee Jones wrote:
> > On Fri, 08 Mar 2024, Michal Hocko wrote:
> > 
> > > On Wed 06-03-24 06:46:11, Greg KH wrote:
> > > [...]
> > > >  Possible unsafe locking scenario:
> > > > 
> > > >        CPU0                    CPU1
> > > >        ----                    ----
> > > >   lock(&svms->lock);
> > > >                                lock(&mm->mmap_lock);
> > > >                                lock(&svms->lock);
> > > >   lock((work_completion)(&svm_bo->eviction_work));
> > > > 
> > > > I believe this cannot really lead to a deadlock in practice, because
> > > > svm_range_evict_svm_bo_worker only takes the mmap_read_lock if the BO
> > > > refcount is non-0. That means it's impossible that svm_range_bo_release
> > > > is running concurrently. However, there is no good way to annotate this.
> > > 
> > > OK, so is this even a bug (not to mention a security/weakness)?
> > 
> > Looks like the patch fixes a warning which can crash some kernels.  So
> > the CVE appears to be fixing that, rather than the impossible deadlock.
> 
> Are you talking about lockdep warning or anything else?

Anything that triggers a BUG() or a WARN() (as per the splat in the
commit message).  Many in-field kernels are configured to panic on
BUG()s and WARN()s, thus triggering them are presently considered local
DoS and attract CVE status.

-- 
Lee Jones [李琼斯]