From 829ee279aed43faa5cb1e4d65c0cad52f2426c53 Mon Sep 17 00:00:00 2001 From: Ladi Prosek Date: Thu, 5 Oct 2017 11:10:23 +0200 Subject: [PATCH] KVM: MMU: always terminate page walks at level 1 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. Fixes: 6bb69c9b69c315200ddc2bc79aee14c0184cf5b2 Cc: stable@vger.kernel.org Cc: Andy Honig Signed-off-by: Ladi Prosek [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 --- arch/x86/kvm/mmu.c | 14 +++++++------- arch/x86/kvm/paging_tmpl.h | 3 ++- 2 files changed, 9 insertions(+), 8 deletions(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 3c25f20115bc..7a69cf053711 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -3973,13 +3973,6 @@ 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 @@ -3987,6 +3980,13 @@ 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; } diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h index 86b68dc5a649..f18d1f8d332b 100644 --- a/arch/x86/kvm/paging_tmpl.h +++ b/arch/x86/kvm/paging_tmpl.h @@ -334,10 +334,11 @@ retry_walk: --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;