[PATCH 1/4] arm64: KVM: perform save/restore of PAR_EL1

Marc Zyngier
2013-07-19T13:54:14Z

Not saving PAR_EL1 is an unfortunate oversight. If the guest
performs an AT* operation and gets scheduled out before reading
the result of the translation from PAREL1, 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@arm.com>
---
arch/arm64/include/asm/kvm_asm.h | 17 ++++++++++-------
arch/arm64/kvm/hyp.S | 10 ++++++++++
arch/arm64/kvm/sys_regs.c | 3 +++
3 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index c92de41..b25763b 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -42,14 +42,15 @@
#define TPIDR_EL1 18 /* Thread ID, Privileged */
#define AMAIR_EL1 19 /* Aux Memory Attribute Indirection Register */
#define CNTKCTL_EL1 20 /* Timer Control Register (EL1) */
+#define PAR_EL1 21 /* Physical Address Register */
/* 32bit specific registers. Keep them at the end of the range */
-#define DACR32_EL2 21 /* Domain Access Control Register */
-#define IFSR32_EL2 22 /* Instruction Fault Status Register */
-#define FPEXC32_EL2 23 /* Floating-Point Exception Control Register */
-#define DBGVCR32_EL2 24 /* Debug Vector Catch Register */
-#define TEECR32_EL1 25 /* ThumbEE Configuration Register */
-#define TEEHBR32_EL1 26 /* ThumbEE Handler Base Register */
-#define NR_SYS_REGS 27
+#define DACR32_EL2 22 /* Domain Access Control Register */
+#define IFSR32_EL2 23 /* Instruction Fault Status Register */
+#define FPEXC32_EL2 24 /* Floating-Point Exception Control Register */
+#define DBGVCR32_EL2 25 /* Debug Vector Catch Register */
+#define TEECR32_EL1 26 /* ThumbEE Configuration Register */
+#define TEEHBR32_EL1 27 /* ThumbEE Handler Base Register */
+#define NR_SYS_REGS 28

/* 32bit mapping */
#define c0_MPIDR (MPIDR_EL1 * 2) /* MultiProcessor ID Register */
@@ -69,6 +70,8 @@
#define c5_AIFSR (AFSR1_EL1 * 2) /* Auxiliary Instr Fault Status R */
#define c6_DFAR (FAR_EL1 * 2) /* Data Fault Address Register */
#define c6_IFAR (c6_DFAR + 1) /* Instruction Fault Address Register */
+#define c7_PAR (PAR_EL1 * 2) /* Physical Address Register */
+#define c7_PAR_high (c7_PAR + 1) /* PAR top 32 bits */
#define c10_PRRR (MAIR_EL1 * 2) /* Primary Region Remap Register */
#define c10_NMRR (c10_PRRR + 1) /* Normal Memory Remap Register */
#define c12_VBAR (VBAR_EL1 * 2) /* Vector Base Address Register */
diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
index ff985e3..218802f 100644
--- a/arch/arm64/kvm/hyp.S
+++ b/arch/arm64/kvm/hyp.S
@@ -214,6 +214,7 @@ __kvm_hyp_code_start:
mrs x21, tpidr_el1
mrs x22, amair_el1
mrs x23, cntkctl_el1
+ mrs x24, par_el1

stp x4, x5, [x3]
stp x6, x7, [x3, #16]
@@ -225,6 +226,7 @@ __kvm_hyp_code_start:
stp x18, x19, [x3, #112]
stp x20, x21, [x3, #128]
stp x22, x23, [x3, #144]
+ str x24, [x3, #160]
.endm

.macro restore_sysregs
@@ -243,6 +245,7 @@ __kvm_hyp_code_start:
ldp x18, x19, [x3, #112]
ldp x20, x21, [x3, #128]
ldp x22, x23, [x3, #144]
+ ldr x24, [x3, #160]

msr vmpidr_el2, x4
msr csselr_el1, x5
@@ -264,6 +267,7 @@ __kvm_hyp_code_start:
msr tpidr_el1, x21
msr amair_el1, x22
msr cntkctl_el1, x23
+ msr par_el1, x24
.endm

.macro skip_32bit_state tmp, target
@@ -753,6 +757,10 @@ el1_trap:
*/
tbnz x1, #7, 1f // S1PTW is set

+ /* Preserve PAR_EL1 */
+ mrs x3, par_el1
+ push x3, xzr
+
/*
* Permission fault, HPFAR_EL2 is invalid.
* Resolve the IPA the hard way using the guest VA.
@@ -766,6 +774,8 @@ el1_trap:

/* Read result */
mrs x3, par_el1
+ pop x0, xzr // Restore PAR_EL1 from the stack
+ msr par_el1, x0
tbnz x3, #0, 3f // Bail out if we failed the translation
ubfx x3, x3, #12, #36 // Extract IPA
lsl x3, x3, #4 // and present it like HPFAR
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 9492360..02e9d09 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -211,6 +211,9 @@ static const struct sys_reg_desc sys_reg_descs[] = {
/* FAR_EL1 */
{ Op0(0b11), Op1(0b000), CRn(0b0110), CRm(0b0000), Op2(0b000),
NULL, reset_unknown, FAR_EL1 },
+ /* PAR_EL1 */
+ { Op0(0b11), Op1(0b000), CRn(0b0111), CRm(0b0100), Op2(0b000),
+ NULL, reset_unknown, PAR_EL1 },

/* PMINTENSET_EL1 */
{ Op0(0b11), Op1(0b000), CRn(0b1001), CRm(0b1110), Op2(0b001),
--
1.8.2.3