On 01/04/2018 07:08 AM, Will Deacon wrote:
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.
Signed-off-by: Will Deacon <[email protected]>
---
arch/arm64/include/asm/sysreg.h | 1 +
arch/arm64/kernel/cpufeature.c | 7 ++++++-
2 files changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 08cc88574659..ae519bbd3f9e 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -437,6 +437,7 @@
#define ID_AA64ISAR1_DPB_SHIFT 0
/* id_aa64pfr0 */
+#define ID_AA64PFR0_CSV3_SHIFT 60
#define ID_AA64PFR0_SVE_SHIFT 32
#define ID_AA64PFR0_GIC_SHIFT 24
#define ID_AA64PFR0_ASIMD_SHIFT 20
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 9f0545dfe497..e11c11bb5b02 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -145,6 +145,7 @@ static const struct arm64_ftr_bits ftr_id_aa64isar1[] = {
};
static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
+ ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE,
ID_AA64PFR0_CSV3_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE,
ID_AA64PFR0_SVE_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE,
ID_AA64PFR0_GIC_SHIFT, 4, 0),
S_ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE,
ID_AA64PFR0_ASIMD_SHIFT, 4, ID_AA64PFR0_ASIMD_NI),
@@ -851,6 +852,8 @@ 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_sanitised_ftr_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",
@@ -862,7 +865,9 @@ 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)
Nit: we only print a message if it's forced on the command line,
can we get a message similar to x86 regardless of state to
clearly indicate if KPTI is enabled?
Thanks,
Laura
