[PATCH 26/52] arm64: entry: Apply BP hardening for high-priority synchronous exceptions

[Alex Shi]

From: Will Deacon <will.deacon at arm.com>

commit 5dfc6ed27710 upstream.

Software-step and PC alignment fault exceptions have higher priority than
instruction abort exceptions, so apply the BP hardening hooks there too
if the user PC appears to reside in kernel space.

Reported-by: Dan Hettena <dhettena at nvidia.com>
Reviewed-by: Marc Zyngier <marc.zyngier at arm.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Alex Shi <alex.shi at linaro.org>

Conflicts:
	expand enable_da_f to 'msr daifclr, #(8 | 4 | 1)'
	in arch/arm64/kernel/entry.S
---
 arch/arm64/kernel/entry.S | 6 ++++--
 arch/arm64/mm/fault.c     | 9 +++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index bdb0139..d50c2fe 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -584,8 +584,10 @@ el0_sp_pc:
 	 * Stack or PC alignment exception handling
 	 */
 	mrs	x26, far_el1
-	// enable interrupts before calling the main handler
-	enable_dbg_and_irq
+	msr	daifclr, #(8 | 4 | 1)
+#ifdef CONFIG_TRACE_IRQFLAGS
+	bl	trace_hardirqs_off
+#endif
 	ct_user_exit
 	mov	x0, x26
 	mov	x1, x25
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index c95b194..6120a14 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -617,6 +617,12 @@ asmlinkage void __exception do_sp_pc_abort(unsigned long addr,
 	struct siginfo info;
 	struct task_struct *tsk = current;
 
+	if (user_mode(regs)) {
+		if (instruction_pointer(regs) > TASK_SIZE)
+			arm64_apply_bp_hardening();
+		local_irq_enable();
+	}
+
 	if (show_unhandled_signals && unhandled_signal(tsk, SIGBUS))
 		pr_info_ratelimited("%s[%d]: %s exception: pc=%p sp=%p\n",
 				    tsk->comm, task_pid_nr(tsk),
@@ -676,6 +682,9 @@ asmlinkage int __exception do_debug_exception(unsigned long addr,
 	if (interrupts_enabled(regs))
 		trace_hardirqs_off();
 
+	if (user_mode(regs) && instruction_pointer(regs) > TASK_SIZE)
+		arm64_apply_bp_hardening();
+
 	if (!inf->fn(addr, esr, regs)) {
 		rv = 1;
 	} else {
-- 
2.7.4