From: Will Deacon will.deacon@arm.com
commit 179a56f6f9fb upstream.
For non-KASLR kernels where the KPTI behaviour has not been overridden on the command line we can use ID_AA64PFR0_EL1.CSV3 to determine whether or not we should unmap the kernel whilst running at EL0.
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 [Alex: s/read_sanitised_ftr_reg/read_system_reg/ to match v4.9 naming] Signed-off-by: Alex Shi alex.shi@linaro.org [v4.9 backport] [Mark: correct zero bits in ftr_id_aa64pfr0 to account for CSV3] Signed-off-by: Mark Rutland mark.rutland@arm.com [v4.9 backport] --- arch/arm64/include/asm/sysreg.h | 1 + arch/arm64/kernel/cpufeature.c | 10 ++++++++-- 2 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h index 7393cc767edb..7cb7f7cdcfbc 100644 --- a/arch/arm64/include/asm/sysreg.h +++ b/arch/arm64/include/asm/sysreg.h @@ -117,6 +117,7 @@ #define ID_AA64ISAR0_AES_SHIFT 4
/* id_aa64pfr0 */ +#define ID_AA64PFR0_CSV3_SHIFT 60 #define ID_AA64PFR0_GIC_SHIFT 24 #define ID_AA64PFR0_ASIMD_SHIFT 20 #define ID_AA64PFR0_FP_SHIFT 16 diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 74b168c51abd..d24e59cedae5 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -93,7 +93,8 @@ static const struct arm64_ftr_bits ftr_id_aa64isar0[] = { };
static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = { - ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 32, 32, 0), + ARM64_FTR_BITS(FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_CSV3_SHIFT, 4, 0), + ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 32, 28, 0), ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 28, 4, 0), ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64PFR0_GIC_SHIFT, 4, 0), S_ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_ASIMD_SHIFT, 4, ID_AA64PFR0_ASIMD_NI), @@ -752,6 +753,8 @@ static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry, int __unused) { + u64 pfr0 = read_system_reg(SYS_ID_AA64PFR0_EL1); + /* Forced on command line? */ if (__kpti_forced) { pr_info_once("kernel page table isolation forced %s by command line option\n", @@ -763,7 +766,9 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry, if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) return true;
- return false; + /* Defer to CPU feature registers */ + return !cpuid_feature_extract_unsigned_field(pfr0, + ID_AA64PFR0_CSV3_SHIFT); }
static int __init parse_kpti(char *str) @@ -865,6 +870,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = { }, #ifdef CONFIG_UNMAP_KERNEL_AT_EL0 { + .desc = "Kernel page table isolation (KPTI)", .capability = ARM64_UNMAP_KERNEL_AT_EL0, .def_scope = SCOPE_SYSTEM, .matches = unmap_kernel_at_el0,