[PATCH] ARM: KVM: perform save/restore of PAR

[Marc Zyngier]

Not saving PAR is an unfortunate oversight. If the guest performs
an AT* operation and gets scheduled out before reading the result
of the translation from PAR, it could become corrupted by another
guest or the host.

Saving this register is made slightly more complicated as KVM also
uses it on the permission fault handling path, leading to an ugly
"stash and restore" sequence. Fortunately, this is already a slow
path so we don't really care. Also, Linux doesn't do any AT*
operation, so Linux guests are not impacted by this bug.

Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
---
 arch/arm/include/asm/kvm_asm.h | 22 ++++++++++++----------
 arch/arm/kvm/coproc.c          |  4 ++++
 arch/arm/kvm/interrupts.S      | 12 +++++++++++-
 arch/arm/kvm/interrupts_head.S | 10 ++++++++--
 4 files changed, 35 insertions(+), 13 deletions(-)

diff --git a/arch/arm/include/asm/kvm_asm.h b/arch/arm/include/asm/kvm_asm.h
index 18d5032..4bb08e3 100644
--- a/arch/arm/include/asm/kvm_asm.h
+++ b/arch/arm/include/asm/kvm_asm.h
@@ -37,16 +37,18 @@
 #define c5_AIFSR	15	/* Auxilary Instrunction Fault Status R */
 #define c6_DFAR		16	/* Data Fault Address Register */
 #define c6_IFAR		17	/* Instruction Fault Address Register */
-#define c9_L2CTLR	18	/* Cortex A15 L2 Control Register */
-#define c10_PRRR	19	/* Primary Region Remap Register */
-#define c10_NMRR	20	/* Normal Memory Remap Register */
-#define c12_VBAR	21	/* Vector Base Address Register */
-#define c13_CID		22	/* Context ID Register */
-#define c13_TID_URW	23	/* Thread ID, User R/W */
-#define c13_TID_URO	24	/* Thread ID, User R/O */
-#define c13_TID_PRIV	25	/* Thread ID, Privileged */
-#define c14_CNTKCTL	26	/* Timer Control Register (PL1) */
-#define NR_CP15_REGS	27	/* Number of regs (incl. invalid) */
+#define c7_PAR		18	/* Physical Address Register */
+#define c7_PAR_high	19	/* PAR top 32 bits */
+#define c9_L2CTLR	20	/* Cortex A15 L2 Control Register */
+#define c10_PRRR	21	/* Primary Region Remap Register */
+#define c10_NMRR	22	/* Normal Memory Remap Register */
+#define c12_VBAR	23	/* Vector Base Address Register */
+#define c13_CID		24	/* Context ID Register */
+#define c13_TID_URW	25	/* Thread ID, User R/W */
+#define c13_TID_URO	26	/* Thread ID, User R/O */
+#define c13_TID_PRIV	27	/* Thread ID, Privileged */
+#define c14_CNTKCTL	28	/* Timer Control Register (PL1) */
+#define NR_CP15_REGS	29	/* Number of regs (incl. invalid) */
 
 #define ARM_EXCEPTION_RESET	  0
 #define ARM_EXCEPTION_UNDEFINED   1
diff --git a/arch/arm/kvm/coproc.c b/arch/arm/kvm/coproc.c
index 8eea97b..4a51990 100644
--- a/arch/arm/kvm/coproc.c
+++ b/arch/arm/kvm/coproc.c
@@ -180,6 +180,10 @@ static const struct coproc_reg cp15_regs[] = {
 			NULL, reset_unknown, c6_DFAR },
 	{ CRn( 6), CRm( 0), Op1( 0), Op2( 2), is32,
 			NULL, reset_unknown, c6_IFAR },
+
+	/* PAR swapped by interrupt.S */
+	{ CRn( 7), Op1( 0), is64, NULL, reset_unknown64, c7_PAR },
+
 	/*
 	 * DC{C,I,CI}SW operations:
 	 */
diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S
index f7793df..d0a8fa3 100644
--- a/arch/arm/kvm/interrupts.S
+++ b/arch/arm/kvm/interrupts.S
@@ -414,6 +414,10 @@ guest_trap:
 	mrcne	p15, 4, r2, c6, c0, 4	@ HPFAR
 	bne	3f
 
+	/* Preserve PAR */
+	mrrc	p15, 0, r0, r1, c7	@ PAR
+	push	{r0, r1}
+
 	/* Resolve IPA using the xFAR */
 	mcr	p15, 0, r2, c7, c8, 0	@ ATS1CPR
 	isb
@@ -424,13 +428,19 @@ guest_trap:
 	lsl	r2, r2, #4
 	orr	r2, r2, r1, lsl #24
 
+	/* Restore PAR */
+	pop	{r0, r1}
+	mcrr	p15, 0, r0, r1, c7	@ PAR
+
 3:	load_vcpu			@ Load VCPU pointer to r0
 	str	r2, [r0, #VCPU_HPFAR]
 
 1:	mov	r1, #ARM_EXCEPTION_HVC
 	b	__kvm_vcpu_return
 
-4:	pop	{r0, r1, r2}		@ Failed translation, return to guest
+4:	pop	{r0, r1}		@ Failed translation, return to guest
+	mcrr	p15, 0, r0, r1, c7	@ PAR
+	pop	{r0, r1, r2}
 	eret
 
 /*
diff --git a/arch/arm/kvm/interrupts_head.S b/arch/arm/kvm/interrupts_head.S
index 3c8f2f0..2478af1 100644
--- a/arch/arm/kvm/interrupts_head.S
+++ b/arch/arm/kvm/interrupts_head.S
@@ -302,11 +302,14 @@ vcpu	.req	r0		@ vcpu pointer always in r0
 	.endif
 
 	mrc	p15, 0, r2, c14, c1, 0	@ CNTKCTL
+	mrrc	p15, 0, r3, r4, c7	@ PAR
 
 	.if \store_to_vcpu == 0
-	push	{r2}
+	push	{r2-r4}
 	.else
 	str	r2, [vcpu, #CP15_OFFSET(c14_CNTKCTL)]
+	add	r12, vcpu, #CP15_OFFSET(c7_PAR)
+	strd	r3, r4, [r12]
 	.endif
 .endm
 
@@ -319,12 +322,15 @@ vcpu	.req	r0		@ vcpu pointer always in r0
  */
 .macro write_cp15_state read_from_vcpu
 	.if \read_from_vcpu == 0
-	pop	{r2}
+	pop	{r2-r4}
 	.else
 	ldr	r2, [vcpu, #CP15_OFFSET(c14_CNTKCTL)]
+	add	r12, vcpu, #CP15_OFFSET(c7_PAR)
+	ldrd	r3, r4, [r12]
 	.endif
 
 	mcr	p15, 0, r2, c14, c1, 0	@ CNTKCTL
+	mcrr	p15, 0, r3, r4, c7	@ PAR
 
 	.if \read_from_vcpu == 0
 	pop	{r2-r12}
-- 
1.8.2.3