On 26/09/2022 15:52, Ovidiu Panait wrote:
From: Mingwei Zhang mizhang@google.com
commit 683412ccf61294d727ead4a73d97397396e69a6b upstream.
Flush the CPU caches when memory is reclaimed from an SEV guest (where reclaim also includes it being unmapped from KVM's memslots). Due to lack of coherency for SEV encrypted memory, failure to flush results in silent data corruption if userspace is malicious/broken and doesn't ensure SEV guest memory is properly pinned and unpinned.
Cache coherency is not enforced across the VM boundary in SEV (AMD APM vol.2 Section 15.34.7). Confidential cachelines, generated by confidential VM guests have to be explicitly flushed on the host side. If a memory page containing dirty confidential cachelines was released by VM and reallocated to another user, the cachelines may corrupt the new user at a later time.
KVM takes a shortcut by assuming all confidential memory remain pinned until the end of VM lifetime. Therefore, KVM does not flush cache at mmu_notifier invalidation events. Because of this incorrect assumption and the lack of cache flushing, malicous userspace can crash the host kernel: creating a malicious VM and continuously allocates/releases unpinned confidential memory pages when the VM is running.
Add cache flush operations to mmu_notifier operations to ensure that any physical memory leaving the guest VM get flushed. In particular, hook mmu_notifier_invalidate_range_start and mmu_notifier_release events and flush cache accordingly. The hook after releasing the mmu lock to avoid contention with other vCPUs.
Cc: stable@vger.kernel.org Suggested-by: Sean Christpherson seanjc@google.com Reported-by: Mingwei Zhang mizhang@google.com Signed-off-by: Mingwei Zhang mizhang@google.com Message-Id: 20220421031407.2516575-4-mizhang@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com [OP: applied kvm_arch_guest_memory_reclaimed() calls in __kvm_set_memory_region() and kvm_mmu_notifier_invalidate_range_start(); OP: adjusted kvm_arch_guest_memory_reclaimed() to not use static_call_cond()] Signed-off-by: Ovidiu Panait ovidiu.panait@windriver.com
Reviewed-by: Liam Merwick liam.merwick@oracle.com
arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/svm.c | 9 +++++++++ arch/x86/kvm/x86.c | 6 ++++++ include/linux/kvm_host.h | 2 ++ virt/kvm/kvm_main.c | 16 ++++++++++++++-- 5 files changed, 32 insertions(+), 2 deletions(-)