Messages in this thread | | | Date | Wed, 20 Mar 2024 18:11:13 +0100 | From | Michal Hocko <> | Subject | Re: CVE-2024-26628: drm/amdkfd: Fix lock dependency warning |
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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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