[PATCH v8 3/6] arm64: ptrauth: Introduce Armv8.3 pointer authentication enhancements

Amit Daniel Kachhap
2020-09-14T08:38:41Z

Some Armv8.3 Pointer Authentication enhancements have been introduced
which are mandatory for Armv8.6 and optional for Armv8.3. These features
are,

* ARMv8.3-PAuth2 - An enhanced PAC generation logic is added which hardens
finding the correct PAC value of the authenticated pointer.

* ARMv8.3-FPAC - Fault is generated now when the ptrauth authentication
instruction fails in authenticating the PAC present in the address.
This is different from earlier case when such failures just adds an
error code in the top byte and waits for subsequent load/store to abort.
The ptrauth instructions which may cause this fault are autiasp, retaa
etc.

The above features are now represented by additional configurations
for the Address Authentication cpufeature and a new ESR exception class.

The userspace fault received in the kernel due to ARMv8.3-FPAC is treated
as Illegal instruction and hence signal SIGILL is injected with ILL_ILLOPN
as the signal code. Note that this is different from earlier ARMv8.3
ptrauth where signal SIGSEGV is issued due to Pointer authentication
failures. The in-kernel PAC fault causes kernel to crash.

Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
---
arch/arm64/include/asm/esr.h | 4 +++-
arch/arm64/include/asm/exception.h | 1 +
arch/arm64/include/asm/sysreg.h | 24 ++++++++++++++++--------
arch/arm64/kernel/entry-common.c | 21 +++++++++++++++++++++
arch/arm64/kernel/traps.c | 12 ++++++++++++
5 files changed, 53 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index 035003acfa87..22c81f1edda2 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -35,7 +35,9 @@
#define ESR_ELx_EC_SYS64 (0x18)
#define ESR_ELx_EC_SVE (0x19)
#define ESR_ELx_EC_ERET (0x1a) /* EL2 only */
-/* Unallocated EC: 0x1b - 0x1E */
+/* Unallocated EC: 0x1B */
+#define ESR_ELx_EC_FPAC (0x1C) /* EL1 and above */
+/* Unallocated EC: 0x1D - 0x1E */
#define ESR_ELx_EC_IMP_DEF (0x1f) /* EL3 only */
#define ESR_ELx_EC_IABT_LOW (0x20)
#define ESR_ELx_EC_IABT_CUR (0x21)
diff --git a/arch/arm64/include/asm/exception.h b/arch/arm64/include/asm/exception.h
index 7577a754d443..99b9383cd036 100644
--- a/arch/arm64/include/asm/exception.h
+++ b/arch/arm64/include/asm/exception.h
@@ -47,4 +47,5 @@ void bad_el0_sync(struct pt_regs *regs, int reason, unsigned int esr);
void do_cp15instr(unsigned int esr, struct pt_regs *regs);
void do_el0_svc(struct pt_regs *regs);
void do_el0_svc_compat(struct pt_regs *regs);
+void do_ptrauth_fault(struct pt_regs *regs, unsigned int esr);
#endif /* __ASM_EXCEPTION_H */
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 554a7e8ecb07..b738bc793369 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -636,14 +636,22 @@
#define ID_AA64ISAR1_APA_SHIFT 4
#define ID_AA64ISAR1_DPB_SHIFT 0

-#define ID_AA64ISAR1_APA_NI 0x0
-#define ID_AA64ISAR1_APA_ARCHITECTED 0x1
-#define ID_AA64ISAR1_API_NI 0x0
-#define ID_AA64ISAR1_API_IMP_DEF 0x1
-#define ID_AA64ISAR1_GPA_NI 0x0
-#define ID_AA64ISAR1_GPA_ARCHITECTED 0x1
-#define ID_AA64ISAR1_GPI_NI 0x0
-#define ID_AA64ISAR1_GPI_IMP_DEF 0x1
+#define ID_AA64ISAR1_APA_NI 0x0
+#define ID_AA64ISAR1_APA_ARCHITECTED 0x1
+#define ID_AA64ISAR1_APA_ARCH_EPAC 0x2
+#define ID_AA64ISAR1_APA_ARCH_EPAC2 0x3
+#define ID_AA64ISAR1_APA_ARCH_EPAC2_FPAC 0x4
+#define ID_AA64ISAR1_APA_ARCH_EPAC2_FPAC_CMB 0x5
+#define ID_AA64ISAR1_API_NI 0x0
+#define ID_AA64ISAR1_API_IMP_DEF 0x1
+#define ID_AA64ISAR1_API_IMP_DEF_EPAC 0x2
+#define ID_AA64ISAR1_API_IMP_DEF_EPAC2 0x3
+#define ID_AA64ISAR1_API_IMP_DEF_EPAC2_FPAC 0x4
+#define ID_AA64ISAR1_API_IMP_DEF_EPAC2_FPAC_CMB 0x5
+#define ID_AA64ISAR1_GPA_NI 0x0
+#define ID_AA64ISAR1_GPA_ARCHITECTED 0x1
+#define ID_AA64ISAR1_GPI_NI 0x0
+#define ID_AA64ISAR1_GPI_IMP_DEF 0x1

/* id_aa64pfr0 */
#define ID_AA64PFR0_CSV3_SHIFT 60
diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index d3be9dbf5490..43d4c329775f 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -66,6 +66,13 @@ static void notrace el1_dbg(struct pt_regs *regs, unsigned long esr)
}
NOKPROBE_SYMBOL(el1_dbg);

+static void notrace el1_fpac(struct pt_regs *regs, unsigned long esr)
+{
+ local_daif_inherit(regs);
+ do_ptrauth_fault(regs, esr);
+}
+NOKPROBE_SYMBOL(el1_fpac);
+
asmlinkage void notrace el1_sync_handler(struct pt_regs *regs)
{
unsigned long esr = read_sysreg(esr_el1);
@@ -92,6 +99,9 @@ asmlinkage void notrace el1_sync_handler(struct pt_regs *regs)
case ESR_ELx_EC_BRK64:
el1_dbg(regs, esr);
break;
+ case ESR_ELx_EC_FPAC:
+ el1_fpac(regs, esr);
+ break;
default:
el1_inv(regs, esr);
}
@@ -227,6 +237,14 @@ static void notrace el0_svc(struct pt_regs *regs)
}
NOKPROBE_SYMBOL(el0_svc);

+static void notrace el0_fpac(struct pt_regs *regs, unsigned long esr)
+{
+ user_exit_irqoff();
+ local_daif_restore(DAIF_PROCCTX);
+ do_ptrauth_fault(regs, esr);
+}
+NOKPROBE_SYMBOL(el0_fpac);
+
asmlinkage void notrace el0_sync_handler(struct pt_regs *regs)
{
unsigned long esr = read_sysreg(esr_el1);
@@ -272,6 +290,9 @@ asmlinkage void notrace el0_sync_handler(struct pt_regs *regs)
case ESR_ELx_EC_BRK64:
el0_dbg(regs, esr);
break;
+ case ESR_ELx_EC_FPAC:
+ el0_fpac(regs, esr);
+ break;
default:
el0_inv(regs, esr);
}
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 29fd00fe94f2..b24f81197a68 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -479,6 +479,17 @@ void do_bti(struct pt_regs *regs)
}
NOKPROBE_SYMBOL(do_bti);

+void do_ptrauth_fault(struct pt_regs *regs, unsigned int esr)
+{
+ /*
+ * Unexpected FPAC exception or pointer authentication failure in
+ * the kernel: kill the task before it does any more harm.
+ */
+ BUG_ON(!user_mode(regs));
+ force_signal_inject(SIGILL, ILL_ILLOPN, regs->pc, esr);
+}
+NOKPROBE_SYMBOL(do_ptrauth_fault);
+
#define __user_cache_maint(insn, address, res) \
if (address >= user_addr_max()) { \
res = -EFAULT; \
@@ -775,6 +786,7 @@ static const char *esr_class_str[] = {
[ESR_ELx_EC_SYS64] = "MSR/MRS (AArch64)",
[ESR_ELx_EC_SVE] = "SVE",
[ESR_ELx_EC_ERET] = "ERET/ERETAA/ERETAB",
+ [ESR_ELx_EC_FPAC] = "FPAC",
[ESR_ELx_EC_IMP_DEF] = "EL3 IMP DEF",
[ESR_ELx_EC_IABT_LOW] = "IABT (lower EL)",
[ESR_ELx_EC_IABT_CUR] = "IABT (current EL)",