[PATCH v3 1/2] arm64: Handle kernel BTI exceptions

[D Scott Phillips]

Send BTI exceptions to the do_bti handler, killing the current task with
SIGSEGV instead of panicking. This is to allow a later patch to apply a
compiler bug workaround.

Signed-off-by: D Scott Phillips <scott at os.amperecomputing.com>
---
 arch/arm64/kernel/entry-common.c | 12 ++++++++++++
 arch/arm64/kernel/traps.c        |  8 ++++++--
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index c75ca36b4a49..dad27e854d8c 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -388,6 +388,15 @@ static void noinstr el1_undef(struct pt_regs *regs)
 	exit_to_kernel_mode(regs);
 }
 
+static void noinstr el1_bti(struct pt_regs *regs)
+{
+	enter_from_kernel_mode(regs);
+	local_daif_inherit(regs);
+	do_bti(regs);
+	local_daif_mask();
+	exit_to_kernel_mode(regs);
+}
+
 static void noinstr el1_dbg(struct pt_regs *regs, unsigned long esr)
 {
 	unsigned long far = read_sysreg(far_el1);
@@ -427,6 +436,9 @@ asmlinkage void noinstr el1h_64_sync_handler(struct pt_regs *regs)
 	case ESR_ELx_EC_UNKNOWN:
 		el1_undef(regs);
 		break;
+	case ESR_ELx_EC_BTI:
+		el1_bti(regs);
+		break;
 	case ESR_ELx_EC_BREAKPT_CUR:
 	case ESR_ELx_EC_SOFTSTP_CUR:
 	case ESR_ELx_EC_WATCHPT_CUR:
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index b7fed33981f7..56e1782fcf54 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -501,8 +501,12 @@ NOKPROBE_SYMBOL(do_undefinstr);
 
 void do_bti(struct pt_regs *regs)
 {
-	BUG_ON(!user_mode(regs));
-	force_signal_inject(SIGILL, ILL_ILLOPC, regs->pc, 0);
+	if (user_mode(regs)) {
+		force_signal_inject(SIGILL, ILL_ILLOPC, regs->pc, 0);
+		return;
+	}
+
+	die("Oops - BTI", regs, 0);
 }
 NOKPROBE_SYMBOL(do_bti);
 
-- 
2.37.2