From: Sean Christopherson seanjc@google.com

mainline inclusion from mainline-v6.8 commit 5ef1d8c1ddbf696e47b226e11888eaf8d9e8e807 category: bugfix CVE: CVE-2024-35791

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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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: 19a23da53932 ("Fix unsynchronized access to sev members through svm_register_enc_region") Reported-by: Gabe Kirkpatrick gkirkpatrick@google.com Cc: Josh Eads josheads@google.com Cc: Peter Gonda pgonda@google.com Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20240217013430.2079561-1-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Ye Bin yebin10@huawei.com --- arch/x86/kvm/svm/sev.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index c2b34998c27d..52e14d6aa496 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -1024,20 +1024,22 @@ 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: