Commit acc730d7 authored by Sean Christopherson's avatar Sean Christopherson Committed by Ye Bin
Browse files

KVM: SVM: Flush pages under kvm->lock to fix UAF in svm_register_enc_region() 

mainline inclusion
from mainline-v6.8
commit 5ef1d8c1ddbf696e47b226e11888eaf8d9e8e807
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9Q8ZA
CVE: CVE-2024-35791

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5ef1d8c1ddbf696e47b226e11888eaf8d9e8e807



--------------------------------

Do the cache flush of converted pages in svm_register_enc_region() before
dropping kvm->lock to fix use-after-free issues where region and/or its
array of pages could be freed by a different task, e.g. if userspace has
__unregister_enc_region_locked() already queued up for the region.

Note, the "obvious" alternative of using local variables doesn't fully
resolve the bug, as region->pages is also dynamically allocated.  I.e. the
region structure itself would be fine, but region->pages could be freed.

Flushing multiple pages under kvm->lock is unfortunate, but the entire
flow is a rare slow path, and the manual flush is only needed on CPUs that
lack coherency for encrypted memory.

Fixes: 19a23da5 ("Fix unsynchronized access to sev members through svm_register_enc_region")
Reported-by: default avatarGabe Kirkpatrick <gkirkpatrick@google.com>
Cc: Josh Eads <josheads@google.com>
Cc: Peter Gonda <pgonda@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20240217013430.2079561-1-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarYe Bin <yebin10@huawei.com>
parent 3e487df5

arch/x86/kvm/svm/sev.c

+9 −7
Original line number Diff line number Diff line
@@ -1027,20 +1027,22 @@ int svm_register_enc_region(struct kvm *kvm, 
		goto e_free;

	}



	region->uaddr = range->addr;

	region->size = range->size;



	list_add_tail(&region->list, &sev->regions_list);

	mutex_unlock(&kvm->lock);



	/*

	 * The guest may change the memory encryption attribute from C=0 -> C=1

	 * or vice versa for this memory range. Lets make sure caches are

	 * flushed to ensure that guest data gets written into memory with

	 * correct C-bit.

	 * correct C-bit.  Note, this must be done before dropping kvm->lock,

	 * as region and its array of pages can be freed by a different task

	 * once kvm->lock is released.

	 */

	sev_clflush_pages(region->pages, region->npages);



	region->uaddr = range->addr;

	region->size = range->size;



	list_add_tail(&region->list, &sev->regions_list);

	mutex_unlock(&kvm->lock);



	return ret;



e_free: