From: Fenghua Yu fenghua.yu@intel.com
mainline inclusion from mainline-v5.18 commit 2667ed10d9f01e250ba806276740782c89d77fda category: bugfix bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I67QJ2 CVE: NA
Intel-SIG: commit 2667ed10d9f0 ("mm: Fix PASID use-after-free issue")
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mm: Fix PASID use-after-free issue
The PASID is being freed too early. It needs to stay around until after device drivers that might be using it have had a chance to clear it out of the hardware.
The relevant refcounts are:
mmget() /mmput() refcount the mm's address space mmgrab()/mmdrop() refcount the mm itself
The PASID is currently tied to the life of the mm's address space and freed in __mmput(). This makes logical sense because the PASID can't be used once the address space is gone.
But, this misses an important point: even after the address space is gone, the PASID will still be programmed into a device. Device drivers might, for instance, still need to flush operations that are outstanding and need to use that PASID. They do this at file->release() time.
Device drivers call the IOMMU driver to hold a reference on the mm itself and drop it at file->release() time. But, the IOMMU driver holds a reference on the mm itself, not the address space. The address space (and the PASID) is long gone by the time the driver tries to clean up. This is effectively a use-after-free bug on the PASID.
To fix this, move the PASID free operation from __mmput() to __mmdrop(). This ensures that the IOMMU driver's existing mmgrab() keeps the PASID allocated until it drops its mm reference.
Fixes: 701fac40384f ("iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit") Reported-by: Zhangfei Gao zhangfei.gao@foxmail.com Suggested-by: Jean-Philippe Brucker jean-philippe@linaro.org Suggested-by: Jacob Pan jacob.jun.pan@linux.intel.com Signed-off-by: Fenghua Yu fenghua.yu@intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-by: Zhangfei Gao zhangfei.gao@foxmail.com Reviewed-by: Jean-Philippe Brucker jean-philippe@linaro.org Link: https://lore.kernel.org/r/20220428180041.806809-1-fenghua.yu@intel.com Signed-off-by: Jason Zeng jason.zeng@intel.com --- kernel/fork.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/fork.c b/kernel/fork.c index 0ac2ae1e8f85..a01cda37dd25 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -688,6 +688,7 @@ void __mmdrop(struct mm_struct *mm) mmu_notifier_subscriptions_destroy(mm); check_mm(mm); put_user_ns(mm->user_ns); + mm_pasid_drop(mm); free_mm(mm); } EXPORT_SYMBOL_GPL(__mmdrop); @@ -1137,7 +1138,6 @@ static inline void __mmput(struct mm_struct *mm) } if (mm->binfmt) module_put(mm->binfmt->module); - mm_pasid_drop(mm); mmdrop(mm); }