From fd19d3b45164466a4adce7cbff448ba9189e1427 Mon Sep 17 00:00:00 2001 From: Ladi Prosek Date: Thu, 5 Oct 2017 11:10:22 +0200 Subject: [PATCH 1/4] KVM: nVMX: update last_nonleaf_level when initializing nested EPT The function updates context->root_level but didn't call update_last_nonleaf_level so the previous and potentially wrong value was used for page walks. For example, a zero value of last_nonleaf_level would allow a potential out-of-bounds access in arch/x86/mmu/paging_tmpl.h's walk_addr_generic function (CVE-2017-12188). Fixes: 155a97a3d7c78b46cef6f1a973c831bc5a4f82bb Signed-off-by: Ladi Prosek Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 106d4a029a8a..3c25f20115bc 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -4555,6 +4555,7 @@ void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly, update_permission_bitmask(vcpu, context, true); update_pkru_bitmask(vcpu, context, true); + update_last_nonleaf_level(vcpu, context); reset_rsvds_bits_mask_ept(vcpu, context, execonly); reset_ept_shadow_zero_bits_mask(vcpu, context, execonly); } From 829ee279aed43faa5cb1e4d65c0cad52f2426c53 Mon Sep 17 00:00:00 2001 From: Ladi Prosek Date: Thu, 5 Oct 2017 11:10:23 +0200 Subject: [PATCH 2/4] 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 @@ 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; From 8eb3f87d903168bdbd1222776a6b1e281f50513e Mon Sep 17 00:00:00 2001 From: Haozhong Zhang Date: Tue, 10 Oct 2017 15:01:22 +0800 Subject: [PATCH 3/4] KVM: nVMX: fix guest CR4 loading when emulating L2 to L1 exit When KVM emulates an exit from L2 to L1, it loads L1 CR4 into the guest CR4. Before this CR4 loading, the guest CR4 refers to L2 CR4. Because these two CR4's are in different levels of guest, we should vmx_set_cr4() rather than kvm_set_cr4() here. The latter, which is used to handle guest writes to its CR4, checks the guest change to CR4 and may fail if the change is invalid. The failure may cause trouble. Consider we start a L1 guest with non-zero L1 PCID in use, (i.e. L1 CR4.PCIDE == 1 && L1 CR3.PCID != 0) and a L2 guest with L2 PCID disabled, (i.e. L2 CR4.PCIDE == 0) and following events may happen: 1. If kvm_set_cr4() is used in load_vmcs12_host_state() to load L1 CR4 into guest CR4 (in VMCS01) for L2 to L1 exit, it will fail because of PCID check. As a result, the guest CR4 recorded in L0 KVM (i.e. vcpu->arch.cr4) is left to the value of L2 CR4. 2. Later, if L1 attempts to change its CR4, e.g., clearing VMXE bit, kvm_set_cr4() in L0 KVM will think L1 also wants to enable PCID, because the wrong L2 CR4 is used by L0 KVM as L1 CR4. As L1 CR3.PCID != 0, L0 KVM will inject GP to L1 guest. Fixes: 4704d0befb072 ("KVM: nVMX: Exiting from L2 to L1") Cc: qemu-stable@nongnu.org Signed-off-by: Haozhong Zhang Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index a2b804e10c95..95a01609d7ee 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -11297,7 +11297,7 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu, /* Same as above - no reason to call set_cr4_guest_host_mask(). */ vcpu->arch.cr4_guest_owned_bits = ~vmcs_readl(CR4_GUEST_HOST_MASK); - kvm_set_cr4(vcpu, vmcs12->host_cr4); + vmx_set_cr4(vcpu, vmcs12->host_cr4); nested_ept_uninit_mmu_context(vcpu); From 8a60aea62100c79fb5d151a1e261f11534c3dbff Mon Sep 17 00:00:00 2001 From: Thomas Huth Date: Mon, 9 Oct 2017 16:34:01 +0200 Subject: [PATCH 4/4] MAINTAINERS: Add Paul Mackerras as maintainer for KVM/powerpc Paul is handling almost all of the powerpc related KVM patches nowadays, so he should be mentioned in the MAINTAINERS file accordingly. Signed-off-by: Thomas Huth Signed-off-by: Paolo Bonzini --- MAINTAINERS | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/MAINTAINERS b/MAINTAINERS index 2d3d750b19c0..6457e5163f93 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -7571,7 +7571,7 @@ F: arch/mips/include/asm/kvm* F: arch/mips/kvm/ KERNEL VIRTUAL MACHINE FOR POWERPC (KVM/powerpc) -M: Alexander Graf +M: Paul Mackerras L: kvm-ppc@vger.kernel.org W: http://www.linux-kvm.org/ T: git git://github.com/agraf/linux-2.6.git