In order to be able to disable BTI at runtime, whether it is
for testing purposes, or to work around HW issues, let's add
support for overriding the ID_AA64PFR1_EL1.BTI field.
This is further mapped on the arm64.nobti command-line alias.
Signed-off-by: Marc Zyngier <m...@kernel.org>
Reviewed-by: Catalin Marinas <catalin.mari...@arm.com>
Acked-by: David Brazdil <dbraz...@google.com>
---
Documentation/admin-guide/kernel-parameters.txt | 3 +++
arch/arm64/include/asm/cpufeature.h | 1 +
arch/arm64/kernel/cpufeature.c | 4 +++-
arch/arm64/kernel/idreg-override.c | 11 +++++++++++
arch/arm64/mm/mmu.c | 2 +-
5 files changed, 19 insertions(+), 2 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt
b/Documentation/admin-guide/kernel-parameters.txt
index 2786fd39a047..7599fd0f1ad7 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -373,6 +373,9 @@
arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
Format: <io>,<irq>,<nodeID>
+ arm64.nobti [ARM64] Unconditionally disable Branch Target
+ Identification support
+
ataflop= [HW,M68k]
atarimouse= [HW,MOUSE] Atari Mouse
diff --git a/arch/arm64/include/asm/cpufeature.h
b/arch/arm64/include/asm/cpufeature.h
index b0ed37da4067..4e2f2de9d0d7 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -819,6 +819,7 @@ static inline unsigned int get_vmid_bits(u64 mmfr1)
}
extern struct arm64_ftr_override id_aa64mmfr1_override;
+extern struct arm64_ftr_override id_aa64pfr1_override;
u32 get_kvm_ipa_limit(void);
void dump_cpu_features(void);
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index c1d6712c4249..bb99ddb212b5 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -558,6 +558,7 @@ static const struct arm64_ftr_bits ftr_raz[] = {
#define ARM64_FTR_REG(id, table) ARM64_FTR_REG_OVERRIDE(id, table,
&no_override)
struct arm64_ftr_override id_aa64mmfr1_override;
+struct arm64_ftr_override id_aa64pfr1_override;
static const struct __ftr_reg_entry {
u32 sys_id;
@@ -593,7 +594,8 @@ 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_id_aa64pfr1),
+ ARM64_FTR_REG_OVERRIDE(SYS_ID_AA64PFR1_EL1, ftr_id_aa64pfr1,
+ &id_aa64pfr1_override),
ARM64_FTR_REG(SYS_ID_AA64ZFR0_EL1, ftr_id_aa64zfr0),
/* Op1 = 0, CRn = 0, CRm = 5 */
diff --git a/arch/arm64/kernel/idreg-override.c
b/arch/arm64/kernel/idreg-override.c
index 3ccf51b84ba4..71349b644246 100644
--- a/arch/arm64/kernel/idreg-override.c
+++ b/arch/arm64/kernel/idreg-override.c
@@ -31,6 +31,15 @@ static const struct ftr_set_desc mmfr1 __initdata = {
},
};
+static const struct ftr_set_desc pfr1 __initdata = {
+ .name = "id_aa64pfr1",
+ .override = &id_aa64pfr1_override,
+ .fields = {
+ { "bt", ID_AA64PFR1_BT_SHIFT },
+ {}
+ },
+};
+
extern struct arm64_ftr_override kaslr_feature_override;
static const struct ftr_set_desc kaslr __initdata = {
@@ -46,6 +55,7 @@ static const struct ftr_set_desc kaslr __initdata = {
static const struct ftr_set_desc * const regs[] __initdata = {
&mmfr1,
+ &pfr1,
&kaslr,
};
@@ -55,6 +65,7 @@ static const struct {
} aliases[] __initdata = {
{ "kvm-arm.mode=nvhe", "id_aa64mmfr1.vh=0" },
{ "kvm-arm.mode=protected", "id_aa64mmfr1.vh=0" },
+ { "arm64.nobti", "id_aa64pfr1.bt=0" },
{ "nokaslr", "kaslr.disabled=1" },
};
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index ae0c3d023824..617e704c980b 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -628,7 +628,7 @@ static bool arm64_early_this_cpu_has_bti(void)
if (!IS_ENABLED(CONFIG_ARM64_BTI_KERNEL))
return false;
- pfr1 = read_sysreg_s(SYS_ID_AA64PFR1_EL1);
+ pfr1 = __read_sysreg_by_encoding(SYS_ID_AA64PFR1_EL1);
return cpuid_feature_extract_unsigned_field(pfr1,
ID_AA64PFR1_BT_SHIFT);
}
--
2.29.2
