From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konstantin Khorenko Date: Mon, 10 Aug 2026 16:14:02 +0200 Subject: [Devel] [PATCH RHEL10 COMMIT] ms/KVM: x86: Check for invalid/obsolete root *after* making MMU pages available In-Reply-To: <20260807134731.2234723-1-ptikhomirov@virtuozzo.com> Message-ID: <202608101414.67AEE23d027571@f0.sw.ru> List-Id: The commit is pushed to "branch-rh10-6.12.0-211.39.1.16.x.vz10-ovz" and will appear at git at bitbucket.org:openvz/vzkernel.git after rh10-6.12.0-211.39.1.16.3.vz10 ------> commit 67f9b973e36d988ee141f0c7881255f77d430a6c Author: Sean Christopherson Date: Fri Aug 7 15:47:27 2026 +0200 ms/KVM: x86: Check for invalid/obsolete root *after* making MMU pages available Check for a "stale" page fault, i.e. for an invalid and/or obsolete root, after making MMU pages available for the shadow MMU. If reclaiming shadow pages zaps an in-use root, i.e. marks it invalid, then KVM will attempt to map memory into an invalid root. On its own, populating an invalid root is "fine", but because child shadow pages inherit their parent's role, any children created during the map/fetch will be created as invalid pages, thus violating KVM's invariant that invalid pages are never on the list of active MMU pages. Note, the underlying flaw has existed since KVM first started tracking invalid roots in 2008 (commit 2e53d63acba7, "KVM: MMU: ignore zapped root pagetables"), but the true badness only came along in 2020 (Linux 5.9) with the invariant that invalid shadow pages can't be on the list of active pages. Note #2, inheriting role.invalid when creating child shadow pages is also far from ideal; that flaw will be addressed separately. Reported-by: Hyunwoo Kim Fixes: f95eec9bed76 ("KVM: x86/mmu: Don't put invalid SPs back on the list of active pages") Cc: stable at vger.kernel.org Signed-off-by: Sean Christopherson Signed-off-by: Paolo Bonzini CVE-2026-64561 [Zapscape] Feature: fix ms/kvm https://virtuozzo.atlassian.net/browse/VSTOR-140678 (cherry picked from commit 2abd5287f08319fa35764566b15c6e22cb1068db) Signed-off-by: Pavel Tikhomirov Reviewed-by: Vasileios Almpanis --- arch/x86/kvm/mmu/mmu.c | 9 +++++---- arch/x86/kvm/mmu/paging_tmpl.h | 10 ++++++---- 2 files changed, 11 insertions(+), 8 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 6472b0e1b45db..04591cfe4f425 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4788,16 +4788,17 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault if (r != RET_PF_CONTINUE) return r; - r = RET_PF_RETRY; write_lock(&vcpu->kvm->mmu_lock); - if (is_page_fault_stale(vcpu, fault)) - goto out_unlock; - r = make_mmu_pages_available(vcpu); if (r) goto out_unlock; + if (is_page_fault_stale(vcpu, fault)) { + r = RET_PF_RETRY; + goto out_unlock; + } + r = direct_map(vcpu, fault); out_unlock: diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h index ed762bb4b007b..af220c9c8ab8d 100644 --- a/arch/x86/kvm/mmu/paging_tmpl.h +++ b/arch/x86/kvm/mmu/paging_tmpl.h @@ -827,15 +827,17 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault } #endif - r = RET_PF_RETRY; write_lock(&vcpu->kvm->mmu_lock); - if (is_page_fault_stale(vcpu, fault)) - goto out_unlock; - r = make_mmu_pages_available(vcpu); if (r) goto out_unlock; + + if (is_page_fault_stale(vcpu, fault)) { + r = RET_PF_RETRY; + goto out_unlock; + } + r = FNAME(fetch)(vcpu, fault, &walker); out_unlock: