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