-From ebe182a7c6221878cbb5d03e1eafa8002494f8cb Mon Sep 17 00:00:00 2001
-From: Ladi Prosek <lprosek@redhat.com>
-Date: Tue, 10 Oct 2017 17:30:59 +0200
-Subject: [CVE-2017-12188 2/2] KVM: MMU: always terminate page walks at level 1
-MIME-Version: 1.0
-Content-Type: text/plain; charset=UTF-8
-Content-Transfer-Encoding: 8bit
-
-is_last_gpte() is not equivalent to the pseudo-code given in commit
-6bb69c9b69c31 ("KVM: MMU: simplify last_pte_bitmap") because an incorrect
-value of last_nonleaf_level may override the result even if level == 1.
-
-It is critical for is_last_gpte() to return true on level == 1 to
-terminate page walks. Otherwise memory corruption may occur as level
-is used as an index to various data structures throughout the page
-walking code. Even though the actual bug would be wherever the MMU is
-initialized (as in the previous patch), be defensive and ensure here
-that is_last_gpte() returns the correct value.
-
-This patch is also enough to fix CVE-2017-12188, and suggested for
-stable and distro kernels.
-
-Fixes: 6bb69c9b69c315200ddc2bc79aee14c0184cf5b2
-Cc: stable@vger.kernel.org
-Cc: Andy Honig <ahonig@google.com>
-Signed-off-by: Ladi Prosek <lprosek@redhat.com>
-[Panic if walk_addr_generic gets an incorrect level; this is a serious
- bug and it's not worth a WARN_ON where the recovery path might hide
- further exploitable issues; suggested by Andrew Honig. - Paolo]
-Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
----
- arch/x86/kvm/paging_tmpl.h | 3 ++-
- arch/x86/kvm/mmu.c | 14 +++++++-------
- 2 files changed, 9 insertions(+), 8 deletions(-)
-
-diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
-index b0454c7e4cff..da06dc8c4fc4 100644
---- a/arch/x86/kvm/paging_tmpl.h
-+++ b/arch/x86/kvm/paging_tmpl.h
-@@ -334,10 +334,11 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
- --walker->level;
-
- index = PT_INDEX(addr, walker->level);
--
- table_gfn = gpte_to_gfn(pte);
- offset = index * sizeof(pt_element_t);
- pte_gpa = gfn_to_gpa(table_gfn) + offset;
-+
-+ BUG_ON(walker->level < 1);
- walker->table_gfn[walker->level - 1] = table_gfn;
- walker->pte_gpa[walker->level - 1] = pte_gpa;
-
-diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
-index ca0112742343..2e4a6732aaa9 100644
---- a/arch/x86/kvm/mmu.c
-+++ b/arch/x86/kvm/mmu.c
-@@ -3934,13 +3934,6 @@ static bool sync_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, gfn_t gfn,
- static inline bool is_last_gpte(struct kvm_mmu *mmu,
- unsigned level, unsigned gpte)
- {
-- /*
-- * PT_PAGE_TABLE_LEVEL always terminates. The RHS has bit 7 set
-- * iff level <= PT_PAGE_TABLE_LEVEL, which for our purpose means
-- * level == PT_PAGE_TABLE_LEVEL; set PT_PAGE_SIZE_MASK in gpte then.
-- */
-- gpte |= level - PT_PAGE_TABLE_LEVEL - 1;
--
- /*
- * The RHS has bit 7 set iff level < mmu->last_nonleaf_level.
- * If it is clear, there are no large pages at this level, so clear
-@@ -3948,6 +3941,13 @@ static inline bool is_last_gpte(struct kvm_mmu *mmu,
- */
- gpte &= level - mmu->last_nonleaf_level;
-
-+ /*
-+ * PT_PAGE_TABLE_LEVEL always terminates. The RHS has bit 7 set
-+ * iff level <= PT_PAGE_TABLE_LEVEL, which for our purpose means
-+ * level == PT_PAGE_TABLE_LEVEL; set PT_PAGE_SIZE_MASK in gpte then.
-+ */
-+ gpte |= level - PT_PAGE_TABLE_LEVEL - 1;
-+
- return gpte & PT_PAGE_SIZE_MASK;
- }
-
---
-2.14.1
-