Re: CVE-2024-26628: drm/amdkfd: Fix lock dependency warning

[Pavel Machek]

On Wed 2024-03-20 15:47:34, 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.

So... because it is possible to configure machine to reboot on
warning, now every warning is a security issue?

Lockdep is for debugging, if someone uses it in production with panic
on reboot, they are getting exactly what they are asking for.

Not a security problem.
								Pavel
-- 
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