Re: [RFC 15/17] arm64: enable ptrauth earlier
From: Amit Kachhap
Date: Sat Oct 06 2018 - 08:52:52 EST
On 10/05/2018 02:17 PM, Kristina Martsenko wrote:
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@xxxxxxx>
---
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)
This function secondary_start_kernel attribute can be set to
__no_ptrauth for better redability as below, although no functionality
is broken as this function does not return.
*/
check_local_cpu_capabilities();
+ ptrauth_cpu_enable();
There are some function calls before so wondering if pointer
authentication and cpu capabilities check required by ptrauth can be
moved still up.
+
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)