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Subject[RFC 15/17] arm64: enable ptrauth earlier
Date
When the kernel is compiled with pointer auth instructions, the boot CPU
needs to start using pointer auth very early, so change the cpucap to
account for this.

A function that enables pointer auth cannot return, so inline such
functions or compile them without pointer auth.

Do not use the cpu_enable callback, to avoid compiling the whole
callchain down to cpu_enable without pointer auth.

Note the change in behavior: if the boot CPU has pointer auth and a late
CPU does not, we panic. Until now we would have just disabled pointer
auth in this case.

Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com>
---
arch/arm64/include/asm/cpufeature.h | 9 +++++++++
arch/arm64/include/asm/pointer_auth.h | 18 ++++++++++++++++++
arch/arm64/kernel/cpufeature.c | 14 ++++----------
arch/arm64/kernel/smp.c | 7 ++++++-
4 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 1717ba1db35d..af4ca92a5fa9 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -292,6 +292,15 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
*/
#define ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE ARM64_CPUCAP_SCOPE_BOOT_CPU

+/*
+ * CPU feature used early in the boot based on the boot CPU. It is safe for a
+ * late CPU to have this feature even though the boot CPU hasn't enabled it,
+ * although the feature will not be used by Linux in this case. If the boot CPU
+ * has enabled this feature already, then every late CPU must have it.
+ */
+#define ARM64_CPUCAP_BOOT_CPU_FEATURE \
+ (ARM64_CPUCAP_SCOPE_BOOT_CPU | ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU)
+
struct arm64_cpu_capabilities {
const char *desc;
u16 capability;
diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
index e60f225d9fa2..0634f06c3af2 100644
--- a/arch/arm64/include/asm/pointer_auth.h
+++ b/arch/arm64/include/asm/pointer_auth.h
@@ -11,6 +11,13 @@

#ifdef CONFIG_ARM64_PTR_AUTH
/*
+ * Compile the function without pointer authentication instructions. This
+ * allows pointer authentication to be enabled/disabled within the function
+ * (but leaves the function unprotected by pointer authentication).
+ */
+#define __no_ptrauth __attribute__((target("sign-return-address=none")))
+
+/*
* Each key is a 128-bit quantity which is split across a pair of 64-bit
* registers (Lo and Hi).
*/
@@ -51,6 +58,15 @@ static inline void ptrauth_keys_switch(struct ptrauth_keys *keys)
__ptrauth_key_install(APIA, keys->apia);
}

+static __always_inline void ptrauth_cpu_enable(void)
+{
+ if (!cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH))
+ return;
+
+ sysreg_clear_set(sctlr_el1, 0, SCTLR_ELx_ENIA);
+ isb();
+}
+
/*
* The EL0 pointer bits used by a pointer authentication code.
* This is dependent on TBI0 being enabled, or bits 63:56 would also apply.
@@ -71,8 +87,10 @@ static inline unsigned long ptrauth_strip_insn_pac(unsigned long ptr)
ptrauth_keys_init(&(tsk)->thread_info.keys_user)

#else /* CONFIG_ARM64_PTR_AUTH */
+#define __no_ptrauth
#define ptrauth_strip_insn_pac(lr) (lr)
#define ptrauth_task_init_user(tsk)
+#define ptrauth_cpu_enable(tsk)
#endif /* CONFIG_ARM64_PTR_AUTH */

#endif /* __ASM_POINTER_AUTH_H */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 3157685aa56a..380ee01145e8 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1040,15 +1040,10 @@ static void cpu_has_fwb(const struct arm64_cpu_capabilities *__unused)
}

#ifdef CONFIG_ARM64_PTR_AUTH
-static void cpu_enable_address_auth(struct arm64_cpu_capabilities const *cap)
-{
- sysreg_clear_set(sctlr_el1, 0, SCTLR_ELx_ENIA);
-}
-
static bool has_address_auth(const struct arm64_cpu_capabilities *entry,
int __unused)
{
- u64 isar1 = read_sanitised_ftr_reg(SYS_ID_AA64ISAR1_EL1);
+ u64 isar1 = read_sysreg(id_aa64isar1_el1);
bool api, apa;

apa = cpuid_feature_extract_unsigned_field(isar1,
@@ -1251,7 +1246,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
{
.desc = "Address authentication (architected algorithm)",
.capability = ARM64_HAS_ADDRESS_AUTH_ARCH,
- .type = ARM64_CPUCAP_SYSTEM_FEATURE,
+ .type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
.sys_reg = SYS_ID_AA64ISAR1_EL1,
.sign = FTR_UNSIGNED,
.field_pos = ID_AA64ISAR1_APA_SHIFT,
@@ -1261,7 +1256,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
{
.desc = "Address authentication (IMP DEF algorithm)",
.capability = ARM64_HAS_ADDRESS_AUTH_IMP_DEF,
- .type = ARM64_CPUCAP_SYSTEM_FEATURE,
+ .type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
.sys_reg = SYS_ID_AA64ISAR1_EL1,
.sign = FTR_UNSIGNED,
.field_pos = ID_AA64ISAR1_API_SHIFT,
@@ -1270,9 +1265,8 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
},
{
.capability = ARM64_HAS_ADDRESS_AUTH,
- .type = ARM64_CPUCAP_SYSTEM_FEATURE,
+ .type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
.matches = has_address_auth,
- .cpu_enable = cpu_enable_address_auth,
},
#endif /* CONFIG_ARM64_PTR_AUTH */
{},
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 25fcd22a4bb2..09690024dce8 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -53,6 +53,7 @@
#include <asm/numa.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
+#include <asm/pointer_auth.h>
#include <asm/processor.h>
#include <asm/smp_plat.h>
#include <asm/sections.h>
@@ -211,6 +212,8 @@ asmlinkage notrace void secondary_start_kernel(void)
*/
check_local_cpu_capabilities();

+ ptrauth_cpu_enable();
+
if (cpu_ops[cpu]->cpu_postboot)
cpu_ops[cpu]->cpu_postboot();

@@ -405,7 +408,7 @@ void __init smp_cpus_done(unsigned int max_cpus)
mark_linear_text_alias_ro();
}

-void __init smp_prepare_boot_cpu(void)
+void __init __no_ptrauth smp_prepare_boot_cpu(void)
{
set_my_cpu_offset(per_cpu_offset(smp_processor_id()));
/*
@@ -414,6 +417,8 @@ void __init smp_prepare_boot_cpu(void)
*/
jump_label_init();
cpuinfo_store_boot_cpu();
+
+ ptrauth_cpu_enable();
}

static u64 __init of_get_cpu_mpidr(struct device_node *dn)
--
2.11.0
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