[3.16.y-ckt stable] Patch "KVM: MMU: fix smap permission check" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    KVM: MMU: fix smap permission check

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt13.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From b577fcb3bf21f20aafd8526498c912ffa9124031 Mon Sep 17 00:00:00 2001
From: Xiao Guangrong <guangrong.xiao at linux.intel.com>
Date: Thu, 7 May 2015 16:20:15 +0800
Subject: KVM: MMU: fix smap permission check

commit 7cbeed9bce7580479bb97457dad220cb3594b875 upstream.

Current permission check assumes that RSVD bit in PFEC is always zero,
however, it is not true since MMIO #PF will use it to quickly identify
MMIO access

Fix it by clearing the bit if walking guest page table is needed

Signed-off-by: Xiao Guangrong <guangrong.xiao at linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/x86/kvm/mmu.h         | 2 ++
 arch/x86/kvm/paging_tmpl.h | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index b982112d2ca5..6baa9221829e 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -174,6 +174,8 @@ static inline bool permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
 	int index = (pfec >> 1) +
 		    (smap >> (X86_EFLAGS_AC_BIT - PFERR_RSVD_BIT + 1));

+	WARN_ON(pfec & PFERR_RSVD_MASK);
+
 	return (mmu->permissions[index] >> pte_access) & 1;
 }

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 410776528265..484711d2c71f 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -706,6 +706,13 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
 					      mmu_is_nested(vcpu));
 		if (likely(r != RET_MMIO_PF_INVALID))
 			return r;
+
+		/*
+		 * page fault with PFEC.RSVD  = 1 is caused by shadow
+		 * page fault, should not be used to walk guest page
+		 * table.
+		 */
+		error_code &= ~PFERR_RSVD_MASK;
 	};

 	r = mmu_topup_memory_caches(vcpu);