linux-kernel - [PATCH 3.12 121/127] KVM: check for !is_zero_pfn() in kvm_is_mmio

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Message-Id: <ad45f7ce6e45cadf13dd92e1b0cfb7525be9a20d.1480062521.git.jslaby@suse.cz>
Date:   Fri, 25 Nov 2016 09:30:34 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 121/127] KVM: check for !is_zero_pfn() in kvm_is_mmio_pfn()

From: Ard Biesheuvel <ard.biesheuvel@...aro.org>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 85c8555ff07ef09261bd50d603cd4290cff5a8cc upstream.

Read-only memory ranges may be backed by the zero page, so avoid
misidentifying it a a MMIO pfn.

This fixes another issue I identified when testing QEMU+KVM_UEFI, where
a read to an uninitialized emulated NOR flash brought in the zero page,
but mapped as a read-write device region, because kvm_is_mmio_pfn()
misidentifies it as a MMIO pfn due to its PG_reserved bit being set.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Fixes: b88657674d39 ("ARM: KVM: user_mem_abort: support stage 2 MMIO page mapping")
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 virt/kvm/kvm_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3351605d2608..e7a1166c3eb4 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -104,7 +104,7 @@ static bool largepages_enabled = true;
 bool kvm_is_mmio_pfn(pfn_t pfn)
 {
 	if (pfn_valid(pfn))
-		return PageReserved(pfn_to_page(pfn));
+		return !is_zero_pfn(pfn) && PageReserved(pfn_to_page(pfn));
 
 	return true;
 }
-- 
2.10.2