From 4868c0ecdb6cfde7c70cf478c46e06bb9c7e5865 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 16 Feb 2024 17:34:30 -0800 Subject: [PATCH] KVM: SVM: Flush pages under kvm->lock to fix UAF in svm_register_enc_region() commit 5ef1d8c1ddbf696e47b226e11888eaf8d9e8e807 upstream. 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 Cc: Josh Eads Cc: Peter Gonda Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson Message-Id: <20240217013430.2079561-1-seanjc@google.com> Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/svm/sev.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 3060fe4e9731..3dc0ee1fe9db 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -1958,20 +1958,22 @@ int sev_mem_enc_register_region(struct kvm *kvm, goto e_free; } + /* + * 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. 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(®ion->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. - */ - sev_clflush_pages(region->pages, region->npages); - return ret; e_free: