[RFC PATCH 1/9] arm64/entry: Bound certain debug exception paths in instrumentation windows

[Hongyan Xia]

From: Hongyan Xia <hongyan.xia at transsion.com>

The el1 debug exception handlers are noinstr, but their payload calls
(do_breakpoint(), do_watchpoint(), try_step_suspended_breakpoints()
and the Cortex-A76 erratum handler) are ordinary instrumentable code.

Mark the boundaries explicitly with instrumentation_begin()/end(), in
the same style as x86 exception entries.

The BRK handlers (do_el1_brk64(), do_el1_softstep()) will be dealt with
in later patches.

Signed-off-by: Hongyan Xia <hongyan.xia at transsion.com>
---
 arch/arm64/kernel/entry-common.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index ceb4eb11232a..466529cce1c3 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -6,6 +6,7 @@
  */
 
 #include <linux/context_tracking.h>
+#include <linux/instrumentation.h>
 #include <linux/irq-entry-common.h>
 #include <linux/kasan.h>
 #include <linux/linkage.h>
@@ -380,7 +381,9 @@ static void noinstr el1_breakpt(struct pt_regs *regs, unsigned long esr)
 
 	state = arm64_enter_el1_dbg(regs);
 	debug_exception_enter(regs);
+	instrumentation_begin();
 	do_breakpoint(esr, regs);
+	instrumentation_end();
 	debug_exception_exit(regs);
 	arm64_exit_el1_dbg(regs, state);
 }
@@ -388,9 +391,15 @@ static void noinstr el1_breakpt(struct pt_regs *regs, unsigned long esr)
 static void noinstr el1_softstp(struct pt_regs *regs, unsigned long esr)
 {
 	irqentry_state_t state;
+	bool handled;
 
 	state = arm64_enter_el1_dbg(regs);
-	if (!cortex_a76_erratum_1463225_debug_handler(regs)) {
+
+	instrumentation_begin();
+	handled = cortex_a76_erratum_1463225_debug_handler(regs);
+	instrumentation_end();
+
+	if (!handled) {
 		debug_exception_enter(regs);
 		/*
 		 * After handling a breakpoint, we suspend the breakpoint
@@ -398,7 +407,11 @@ static void noinstr el1_softstp(struct pt_regs *regs, unsigned long esr)
 		 * If we are stepping a suspended breakpoint there's nothing more to do:
 		 * the single-step is complete.
 		 */
-		if (!try_step_suspended_breakpoints(regs))
+		instrumentation_begin();
+		handled = try_step_suspended_breakpoints(regs);
+		instrumentation_end();
+
+		if (!handled)
 			do_el1_softstep(esr, regs);
 		debug_exception_exit(regs);
 	}
@@ -413,7 +426,9 @@ static void noinstr el1_watchpt(struct pt_regs *regs, unsigned long esr)
 
 	state = arm64_enter_el1_dbg(regs);
 	debug_exception_enter(regs);
+	instrumentation_begin();
 	do_watchpoint(far, esr, regs);
+	instrumentation_end();
 	debug_exception_exit(regs);
 	arm64_exit_el1_dbg(regs, state);
 }
-- 
2.47.3