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Message-ID: <ZfsYsQUoizXAJR9N@tiehlicka>
Date: Wed, 20 Mar 2024 18:11:13 +0100
From: Michal Hocko <mhocko@...e.com>
To: Lee Jones <lee@...nel.org>
Cc: cve@...nel.org, linux-kernel@...r.kernel.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Felix Kuehling <felix.kuehling@....com>
Subject: Re: CVE-2024-26628: drm/amdkfd: Fix lock dependency warning
On Wed 20-03-24 16:51:27, Lee Jones wrote:
> On Wed, 20 Mar 2024, Lee Jones wrote:
>
> > 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.
yes I do agree that WARN() should be treated same as BUG() if
triggerable by an user (for reasons you have mentioned). Lockdep is a
different thing as you follow up below.
> We have discussed this internally and agree with your thinking.
>
> The splat in the circular lockdep detection code appears to be generated
> using some stacked pr_warn() calls, rather than a WARN().
>
> Thus, CVE-2024-26628 has now been rejected.
>
> https://lore.kernel.org/all/20240320164818.3778843-2-lee@kernel.org/
>
> Thank you for your input Michal.
Thanks!
--
Michal Hocko
SUSE Labs
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