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authorFenghua Yu <fenghua.yu@intel.com>2022-04-28 21:00:41 +0300
committerThomas Gleixner <tglx@linutronix.de>2022-05-01 11:17:17 +0300
commit2667ed10d9f01e250ba806276740782c89d77fda (patch)
tree336c0eee41ba462a199134a9c7c2d6c3749ea382 /kernel/fork.c
parent57ae8a492116910bad2b3497ffe555b3a4b4180f (diff)
downloadlinux-2667ed10d9f01e250ba806276740782c89d77fda.tar.xz
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
Diffstat (limited to 'kernel/fork.c')
-rw-r--r--kernel/fork.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 9796897560ab..35a3beff140b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -792,6 +792,7 @@ 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);
@@ -1190,7 +1191,6 @@ static inline void __mmput(struct mm_struct *mm)
}
if (mm->binfmt)
module_put(mm->binfmt->module);
- mm_pasid_drop(mm);
mmdrop(mm);
}