arm64: unwind: strip PAC from kernel addresses

When we enable pointer authentication in the kernel, LR values saved to
the stack will have a PAC which we must strip in order to retrieve the
real return address.

Strip PACs when unwinding the stack in order to account for this.

When function graph tracer is used with patchable-function-entry then
return_to_handler will also have pac bits so strip it too.

Reviewed-by: Kees Cook <[email protected]>
Acked-by: Catalin Marinas <[email protected]>
Reviewed-by: James Morse <[email protected]>
Signed-off-by: Mark Rutland <[email protected]>
Signed-off-by: Kristina Martsenko <[email protected]>
[Amit: Re-position ptrauth_strip_insn_pac, comment]
Signed-off-by: Amit Daniel Kachhap <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>

Author: mrutland-arm

arch/arm64/kernel/stacktrace.c

@@ -14,6 +14,7 @@
 #include <linux/stacktrace.h>
 
 #include <asm/irq.h>
+#include <asm/pointer_auth.h>
 #include <asm/stack_pointer.h>
 #include <asm/stacktrace.h>
 
@@ -86,7 +87,7 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	if (tsk->ret_stack &&
-			(frame->pc == (unsigned long)return_to_handler)) {
+		(ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) {
 		struct ftrace_ret_stack *ret_stack;
 		/*
 		 * This is a case where function graph tracer has
@@ -101,6 +102,8 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 	}
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 
+	frame->pc = ptrauth_strip_insn_pac(frame->pc);
+
 	/*
 	 * Frames created upon entry from EL0 have NULL FP and PC values, so
 	 * don't bother reporting these. Frames created by __noreturn functions