Patch "MIPS: KVM: Fix mapped fault broken commpage handling" has been added to the 4.7-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    MIPS: KVM: Fix mapped fault broken commpage handling

to the 4.7-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mips-kvm-fix-mapped-fault-broken-commpage-handling.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From c604cffa93478f8888bec62b23d6073dad03d43a Mon Sep 17 00:00:00 2001
From: James Hogan <james.hogan@imgtec.com>
Date: Thu, 11 Aug 2016 11:58:12 +0100
Subject: MIPS: KVM: Fix mapped fault broken commpage handling
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: James Hogan <james.hogan@imgtec.com>

commit c604cffa93478f8888bec62b23d6073dad03d43a upstream.

kvm_mips_handle_mapped_seg_tlb_fault() appears to map the guest page at
virtual address 0 to PFN 0 if the guest has created its own mapping
there. The intention is unclear, but it may have been an attempt to
protect the zero page from being mapped to anything but the comm page in
code paths you wouldn't expect from genuine commpage accesses (guest
kernel mode cache instructions on that address, hitting trapping
instructions when executing from that address with a coincidental TLB
eviction during the KVM handling, and guest user mode accesses to that
address).

Fix this to check for mappings exactly at KVM_GUEST_COMMPAGE_ADDR (it
may not be at address 0 since commit 42aa12e74e91 ("MIPS: KVM: Move
commpage so 0x0 is unmapped")), and set the corresponding EntryLo to be
interpreted as 0 (invalid).

Fixes: 858dd5d45733 ("KVM/MIPS32: MMU/TLB operations for the Guest.")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Cc: <stable@vger.kernel.org> # 3.10.x-
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
[james.hogan@imgtec.com: Backport to v4.7]
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/mips/kvm/tlb.c |   45 ++++++++++++++++++++++++++-------------------
 1 file changed, 26 insertions(+), 19 deletions(-)

--- a/arch/mips/kvm/tlb.c
+++ b/arch/mips/kvm/tlb.c
@@ -373,25 +373,32 @@ int kvm_mips_handle_mapped_seg_tlb_fault
 	unsigned long entryhi = 0, entrylo0 = 0, entrylo1 = 0;
 	struct kvm *kvm = vcpu->kvm;
 	kvm_pfn_t pfn0, pfn1;
+	long tlb_lo[2];
 	int ret;
 
-	if ((tlb->tlb_hi & VPN2_MASK) == 0) {
-		pfn0 = 0;
-		pfn1 = 0;
-	} else {
-		if (kvm_mips_map_page(kvm, mips3_tlbpfn_to_paddr(tlb->tlb_lo0)
-					   >> PAGE_SHIFT) < 0)
-			return -1;
-
-		if (kvm_mips_map_page(kvm, mips3_tlbpfn_to_paddr(tlb->tlb_lo1)
-					   >> PAGE_SHIFT) < 0)
-			return -1;
-
-		pfn0 = kvm->arch.guest_pmap[mips3_tlbpfn_to_paddr(tlb->tlb_lo0)
-					    >> PAGE_SHIFT];
-		pfn1 = kvm->arch.guest_pmap[mips3_tlbpfn_to_paddr(tlb->tlb_lo1)
-					    >> PAGE_SHIFT];
-	}
+	tlb_lo[0] = tlb->tlb_lo0;
+	tlb_lo[1] = tlb->tlb_lo1;
+
+	/*
+	 * The commpage address must not be mapped to anything else if the guest
+	 * TLB contains entries nearby, or commpage accesses will break.
+	 */
+	if (!((tlb->tlb_hi ^ KVM_GUEST_COMMPAGE_ADDR) &
+			VPN2_MASK & (PAGE_MASK << 1)))
+		tlb_lo[(KVM_GUEST_COMMPAGE_ADDR >> PAGE_SHIFT) & 1] = 0;
+
+	if (kvm_mips_map_page(kvm, mips3_tlbpfn_to_paddr(tlb_lo[0])
+				   >> PAGE_SHIFT) < 0)
+		return -1;
+
+	if (kvm_mips_map_page(kvm, mips3_tlbpfn_to_paddr(tlb_lo[1])
+				   >> PAGE_SHIFT) < 0)
+		return -1;
+
+	pfn0 = kvm->arch.guest_pmap[mips3_tlbpfn_to_paddr(tlb_lo[0])
+				    >> PAGE_SHIFT];
+	pfn1 = kvm->arch.guest_pmap[mips3_tlbpfn_to_paddr(tlb_lo[1])
+				    >> PAGE_SHIFT];
 
 	if (hpa0)
 		*hpa0 = pfn0 << PAGE_SHIFT;
@@ -401,9 +408,9 @@ int kvm_mips_handle_mapped_seg_tlb_fault
 
 	/* Get attributes from the Guest TLB */
 	entrylo0 = mips3_paddr_to_tlbpfn(pfn0 << PAGE_SHIFT) | (0x3 << 3) |
-		   (tlb->tlb_lo0 & MIPS3_PG_D) | (tlb->tlb_lo0 & MIPS3_PG_V);
+		   (tlb_lo[0] & MIPS3_PG_D) | (tlb_lo[0] & MIPS3_PG_V);
 	entrylo1 = mips3_paddr_to_tlbpfn(pfn1 << PAGE_SHIFT) | (0x3 << 3) |
-		   (tlb->tlb_lo1 & MIPS3_PG_D) | (tlb->tlb_lo1 & MIPS3_PG_V);
+		   (tlb_lo[1] & MIPS3_PG_D) | (tlb_lo[1] & MIPS3_PG_V);
 
 	kvm_debug("@ %#lx tlb_lo0: 0x%08lx tlb_lo1: 0x%08lx\n", vcpu->arch.pc,
 		  tlb->tlb_lo0, tlb->tlb_lo1);


Patches currently in stable-queue which might be from james.hogan@imgtec.com are

queue-4.7/mips-kvm-add-missing-gfn-range-check.patch
queue-4.7/mips-kvm-propagate-kseg0-mapped-tlb-fault-errors.patch
queue-4.7/mips-kvm-fix-mapped-fault-broken-commpage-handling.patch
queue-4.7/mips-kvm-fix-gfn-range-check-in-kseg0-tlb-faults.patch