linux-kernel - [PATCH 3.16 033/254] arm64: KVM: fix VTTBR_BADDR_MASK BUG

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Message-ID: <lsq.1519831218.496839452@decadent.org.uk>
Date:   Wed, 28 Feb 2018 15:20:18 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Marc Zyngier" <marc.zyngier@....com>,
        "Suzuki K Poulose" <suzuki.poulose@....com>,
        "Kristina Martsenko" <kristina.martsenko@....com>,
        "Christoffer Dall" <christoffer.dall@...aro.org>
Subject: [PATCH 3.16 033/254] arm64: KVM: fix VTTBR_BADDR_MASK BUG_ON
 off-by-one

3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Kristina Martsenko <kristina.martsenko@....com>

commit 26aa7b3b1c0fb3f1a6176a0c1847204ef4355693 upstream.

VTTBR_BADDR_MASK is used to sanity check the size and alignment of the
VTTBR address. It seems to currently be off by one, thereby only
allowing up to 47-bit addresses (instead of 48-bit) and also
insufficiently checking the alignment. This patch fixes it.

As an example, with 4k pages, before this patch we have:

  PHYS_MASK_SHIFT = 48
  VTTBR_X = 37 - 24 = 13
  VTTBR_BADDR_SHIFT = 13 - 1 = 12
  VTTBR_BADDR_MASK = ((1 << 35) - 1) << 12 = 0x00007ffffffff000

Which is wrong, because the mask doesn't allow bit 47 of the VTTBR
address to be set, and only requires the address to be 12-bit (4k)
aligned, while it actually needs to be 13-bit (8k) aligned because we
concatenate two 4k tables.

With this patch, the mask becomes 0x0000ffffffffe000, which is what we
want.

Fixes: 0369f6a34b9f ("arm64: KVM: EL2 register definitions")
Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
Reviewed-by: Christoffer Dall <christoffer.dall@...aro.org>
Signed-off-by: Kristina Martsenko <kristina.martsenko@....com>
Signed-off-by: Marc Zyngier <marc.zyngier@....com>
Signed-off-by: Christoffer Dall <christoffer.dall@...aro.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/arm64/include/asm/kvm_arm.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/arch/arm64/include/asm/kvm_arm.h
+++ b/arch/arm64/include/asm/kvm_arm.h
@@ -164,8 +164,7 @@
 #define VTTBR_X		(37 - VTCR_EL2_T0SZ_40B)
 #endif
 
-#define VTTBR_BADDR_SHIFT (VTTBR_X - 1)
-#define VTTBR_BADDR_MASK  (((UL(1) << (PHYS_MASK_SHIFT - VTTBR_X)) - 1) << VTTBR_BADDR_SHIFT)
+#define VTTBR_BADDR_MASK  (((UL(1) << (PHYS_MASK_SHIFT - VTTBR_X)) - 1) << VTTBR_X)
 #define VTTBR_VMID_SHIFT  (UL(48))
 #define VTTBR_VMID_MASK	  (UL(0xFF) << VTTBR_VMID_SHIFT)