From: Sean Christopherson <seanjc@google.com> stable inclusion from stable-v6.6.144 commit 488e386484ec8c0e558be6e156edf34ed9f4d5c8 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/16072 CVE: CVE-2026-53359 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- commit 0cb2af2ea66ad8ff195c156ea690f11216285bdf upstream. The shadow MMU computes GFNs for direct shadow pages using sp->gfn plus the SPTE index. This assumption breaks for shadow paging if the guest page tables are modified between VM entries (similar to commit aad885e77496, "KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE", 2026-03-27). The flow is as follows: - a PDE is installed for a 2MB mapping, and a page in that area is accessed. KVM creates a kvm_mmu_page consisting of 512 4KB pages; the kvm_mmu_page is marked by FNAME(fetch) as direct-mapped because the guest's mapping is a huge page (and thus contiguous). - the PDE mapping is changed from outside the guest. - the guest accesses another page in the same 2MB area. KVM installs a new leaf SPTE and rmap entry; the SPTE uses the "correct" GFN (i.e. based on the new mapping, as changed in the previous step) but that GFN is outside of the [sp->gfn, sp->gfn + 511] range; therefore the rmap entry cannot be found and removed when the kvm_mmu_page is zapped. - the memslot that covers the first 2MB mapping is deleted, and the kvm_mmu_page for the now-invalid GPA is zapped. However, rmap_remove() only looks at the [sp->gfn, sp->gfn + 511] range established in step 1, and fails to find the rmap entry that was recorded by step 3. - any operation that causes an rmap walk for the same page accessed by step 3 then walks a stale rmap and dereferences a freed kvm_mmu_page. This includes dirty logging or MMU notifier invalidations (e.g., from MADV_DONTNEED). The underlying issue is that KVM's walking of shadow PTEs assumes that if a SPTE is present when KVM wants to install a non-leaf SPTE, then the existing kvm_mmu_page must be for the correct gfn. Because the only way for the gfn to be wrong is if KVM messed up and failed to zap a SPTE... which shouldn't happen, but *actually* only happens in response to a guest write. That bug dates back literally forever, as even the first version of KVM assumes that the GFN matches and walks into the "wrong" shadow page. However, that was only an imprecision until 2032a93d66fa ("KVM: MMU: Don't allocate gfns page for direct mmu pages") came along. Fix it by checking for a target gfn mismatch and zapping the existing SPTE. That way the old SP and rmap entries are gone, KVM installs the rmap in the right location, and everyone is happy. Fixes: 2032a93d66fa ("KVM: MMU: Don't allocate gfns page for direct mmu pages") Fixes: 6aa8b732ca01 ("kvm: userspace interface") Reported-by: Alexander Bulekov <bkov@amazon.com> Reported-by: Fred Griffoul <fgriffo@amazon.co.uk> Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson <seanjc@google.com> Link: https://patch.msgid.link/20260503201029.106481-1-pbonzini@redhat.com/ Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Sasha Levin <sashal@kernel.org> Conflicts: arch/x86/kvm/mmu/mmu.c [20ba462dfda6 ("KVM: x86/mmu: Convert "runtime" WARN_ON() assertions to WARN_ON_ONCE()") not merged] Signed-off-by: Zhang Kunbo <zhangkunbo@huawei.com> --- arch/x86/kvm/mmu/mmu.c | 35 ++++++++++++++--------------------- 1 file changed, 14 insertions(+), 21 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 6ee54414295b..f281f8952608 100755 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -169,6 +169,8 @@ struct kmem_cache *mmu_page_header_cache; static struct percpu_counter kvm_total_used_mmu_pages; static void mmu_spte_set(u64 *sptep, u64 spte); +static int mmu_page_zap_pte(struct kvm *kvm, struct kvm_mmu_page *sp, + u64 *spte, struct list_head *invalid_list); struct kvm_mmu_role_regs { const unsigned long cr0; @@ -1176,19 +1178,6 @@ static void drop_spte(struct kvm *kvm, u64 *sptep) rmap_remove(kvm, sptep); } -static void drop_large_spte(struct kvm *kvm, u64 *sptep, bool flush) -{ - struct kvm_mmu_page *sp; - - sp = sptep_to_sp(sptep); - WARN_ON(sp->role.level == PG_LEVEL_4K); - - drop_spte(kvm, sptep); - - if (flush) - kvm_flush_remote_tlbs_sptep(kvm, sptep); -} - /* * Write-protect on the specified @sptep, @pt_protect indicates whether * spte write-protection is caused by protecting shadow page table. @@ -2259,7 +2248,8 @@ static struct kvm_mmu_page *kvm_mmu_get_child_sp(struct kvm_vcpu *vcpu, { union kvm_mmu_page_role role; - if (is_shadow_present_pte(*sptep) && !is_large_pte(*sptep)) + if (is_shadow_present_pte(*sptep) && !is_large_pte(*sptep) && + spte_to_child_sp(*sptep) && spte_to_child_sp(*sptep)->gfn == gfn) return ERR_PTR(-EEXIST); role = kvm_mmu_child_role(sptep, direct, access); @@ -2337,13 +2327,16 @@ static void __link_shadow_page(struct kvm *kvm, BUILD_BUG_ON(VMX_EPT_WRITABLE_MASK != PT_WRITABLE_MASK); - /* - * If an SPTE is present already, it must be a leaf and therefore - * a large one. Drop it, and flush the TLB if needed, before - * installing sp. - */ - if (is_shadow_present_pte(*sptep)) - drop_large_spte(kvm, sptep, flush); + if (is_shadow_present_pte(*sptep)) { + struct kvm_mmu_page *parent_sp; + LIST_HEAD(invalid_list); + + parent_sp = sptep_to_sp(sptep); + WARN_ON_ONCE(parent_sp->role.level == PG_LEVEL_4K); + + mmu_page_zap_pte(kvm, parent_sp, sptep, &invalid_list); + kvm_mmu_remote_flush_or_zap(kvm, &invalid_list, true); + } spte = make_nonleaf_spte(sp->spt, sp_ad_disabled(sp)); -- 2.34.1