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Subject[PATCH 4.19 048/114] arm64: cpufeature: Detect SSBS and advertise to userspace
Date
From: Will Deacon <will.deacon@arm.com>

commit d71be2b6c0e19180b5f80a6d42039cc074a693a2 upstream.

Armv8.5 introduces a new PSTATE bit known as Speculative Store Bypass
Safe (SSBS) which can be used as a mitigation against Spectre variant 4.

Additionally, a CPU may provide instructions to manipulate PSTATE.SSBS
directly, so that userspace can toggle the SSBS control without trapping
to the kernel.

This patch probes for the existence of SSBS and advertise the new instructions
to userspace if they exist.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm64/include/asm/cpucaps.h | 3 ++-
arch/arm64/include/asm/sysreg.h | 16 ++++++++++++----
arch/arm64/include/uapi/asm/hwcap.h | 1 +
arch/arm64/kernel/cpufeature.c | 19 +++++++++++++++++--
arch/arm64/kernel/cpuinfo.c | 1 +
5 files changed, 33 insertions(+), 7 deletions(-)

--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -52,7 +52,8 @@
#define ARM64_MISMATCHED_CACHE_TYPE 31
#define ARM64_HAS_STAGE2_FWB 32
#define ARM64_WORKAROUND_1463225 33
+#define ARM64_SSBS 34

-#define ARM64_NCAPS 34
+#define ARM64_NCAPS 35

#endif /* __ASM_CPUCAPS_H */
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -419,6 +419,7 @@
#define SYS_ICH_LR15_EL2 __SYS__LR8_EL2(7)

/* Common SCTLR_ELx flags. */
+#define SCTLR_ELx_DSSBS (1UL << 44)
#define SCTLR_ELx_EE (1 << 25)
#define SCTLR_ELx_IESB (1 << 21)
#define SCTLR_ELx_WXN (1 << 19)
@@ -439,7 +440,7 @@
(1 << 10) | (1 << 13) | (1 << 14) | (1 << 15) | \
(1 << 17) | (1 << 20) | (1 << 24) | (1 << 26) | \
(1 << 27) | (1 << 30) | (1 << 31) | \
- (0xffffffffUL << 32))
+ (0xffffefffUL << 32))

#ifdef CONFIG_CPU_BIG_ENDIAN
#define ENDIAN_SET_EL2 SCTLR_ELx_EE
@@ -453,7 +454,7 @@
#define SCTLR_EL2_SET (SCTLR_ELx_IESB | ENDIAN_SET_EL2 | SCTLR_EL2_RES1)
#define SCTLR_EL2_CLEAR (SCTLR_ELx_M | SCTLR_ELx_A | SCTLR_ELx_C | \
SCTLR_ELx_SA | SCTLR_ELx_I | SCTLR_ELx_WXN | \
- ENDIAN_CLEAR_EL2 | SCTLR_EL2_RES0)
+ SCTLR_ELx_DSSBS | ENDIAN_CLEAR_EL2 | SCTLR_EL2_RES0)

#if (SCTLR_EL2_SET ^ SCTLR_EL2_CLEAR) != 0xffffffffffffffff
#error "Inconsistent SCTLR_EL2 set/clear bits"
@@ -477,7 +478,7 @@
(1 << 29))
#define SCTLR_EL1_RES0 ((1 << 6) | (1 << 10) | (1 << 13) | (1 << 17) | \
(1 << 27) | (1 << 30) | (1 << 31) | \
- (0xffffffffUL << 32))
+ (0xffffefffUL << 32))

#ifdef CONFIG_CPU_BIG_ENDIAN
#define ENDIAN_SET_EL1 (SCTLR_EL1_E0E | SCTLR_ELx_EE)
@@ -494,7 +495,7 @@
ENDIAN_SET_EL1 | SCTLR_EL1_UCI | SCTLR_EL1_RES1)
#define SCTLR_EL1_CLEAR (SCTLR_ELx_A | SCTLR_EL1_CP15BEN | SCTLR_EL1_ITD |\
SCTLR_EL1_UMA | SCTLR_ELx_WXN | ENDIAN_CLEAR_EL1 |\
- SCTLR_EL1_RES0)
+ SCTLR_ELx_DSSBS | SCTLR_EL1_RES0)

#if (SCTLR_EL1_SET ^ SCTLR_EL1_CLEAR) != 0xffffffffffffffff
#error "Inconsistent SCTLR_EL1 set/clear bits"
@@ -544,6 +545,13 @@
#define ID_AA64PFR0_EL0_64BIT_ONLY 0x1
#define ID_AA64PFR0_EL0_32BIT_64BIT 0x2

+/* id_aa64pfr1 */
+#define ID_AA64PFR1_SSBS_SHIFT 4
+
+#define ID_AA64PFR1_SSBS_PSTATE_NI 0
+#define ID_AA64PFR1_SSBS_PSTATE_ONLY 1
+#define ID_AA64PFR1_SSBS_PSTATE_INSNS 2
+
/* id_aa64mmfr0 */
#define ID_AA64MMFR0_TGRAN4_SHIFT 28
#define ID_AA64MMFR0_TGRAN64_SHIFT 24
--- a/arch/arm64/include/uapi/asm/hwcap.h
+++ b/arch/arm64/include/uapi/asm/hwcap.h
@@ -48,5 +48,6 @@
#define HWCAP_USCAT (1 << 25)
#define HWCAP_ILRCPC (1 << 26)
#define HWCAP_FLAGM (1 << 27)
+#define HWCAP_SSBS (1 << 28)

#endif /* _UAPI__ASM_HWCAP_H */
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -164,6 +164,11 @@ static const struct arm64_ftr_bits ftr_i
ARM64_FTR_END,
};

+static const struct arm64_ftr_bits ftr_id_aa64pfr1[] = {
+ ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR1_SSBS_SHIFT, 4, ID_AA64PFR1_SSBS_PSTATE_NI),
+ ARM64_FTR_END,
+};
+
static const struct arm64_ftr_bits ftr_id_aa64mmfr0[] = {
/*
* We already refuse to boot CPUs that don't support our configured
@@ -379,7 +384,7 @@ static const struct __ftr_reg_entry {

/* Op1 = 0, CRn = 0, CRm = 4 */
ARM64_FTR_REG(SYS_ID_AA64PFR0_EL1, ftr_id_aa64pfr0),
- ARM64_FTR_REG(SYS_ID_AA64PFR1_EL1, ftr_raz),
+ ARM64_FTR_REG(SYS_ID_AA64PFR1_EL1, ftr_id_aa64pfr1),
ARM64_FTR_REG(SYS_ID_AA64ZFR0_EL1, ftr_raz),

/* Op1 = 0, CRn = 0, CRm = 5 */
@@ -669,7 +674,6 @@ void update_cpu_features(int cpu,

/*
* EL3 is not our concern.
- * ID_AA64PFR1 is currently RES0.
*/
taint |= check_update_ftr_reg(SYS_ID_AA64PFR0_EL1, cpu,
info->reg_id_aa64pfr0, boot->reg_id_aa64pfr0);
@@ -1254,6 +1258,16 @@ static const struct arm64_cpu_capabiliti
.cpu_enable = cpu_enable_hw_dbm,
},
#endif
+ {
+ .desc = "Speculative Store Bypassing Safe (SSBS)",
+ .capability = ARM64_SSBS,
+ .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE,
+ .matches = has_cpuid_feature,
+ .sys_reg = SYS_ID_AA64PFR1_EL1,
+ .field_pos = ID_AA64PFR1_SSBS_SHIFT,
+ .sign = FTR_UNSIGNED,
+ .min_field_value = ID_AA64PFR1_SSBS_PSTATE_ONLY,
+ },
{},
};

@@ -1299,6 +1313,7 @@ static const struct arm64_cpu_capabiliti
#ifdef CONFIG_ARM64_SVE
HWCAP_CAP(SYS_ID_AA64PFR0_EL1, ID_AA64PFR0_SVE_SHIFT, FTR_UNSIGNED, ID_AA64PFR0_SVE, CAP_HWCAP, HWCAP_SVE),
#endif
+ HWCAP_CAP(SYS_ID_AA64PFR1_EL1, ID_AA64PFR1_SSBS_SHIFT, FTR_UNSIGNED, ID_AA64PFR1_SSBS_PSTATE_INSNS, CAP_HWCAP, HWCAP_SSBS),
{},
};

--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c
@@ -81,6 +81,7 @@ static const char *const hwcap_str[] = {
"uscat",
"ilrcpc",
"flagm",
+ "ssbs",
NULL
};


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