Add an indication for an outermost frame to the unwind user frame
structure and stop unwinding when reaching an outermost frame.

This will be used by unwind user sframe, as SFrame may represent an
undefined return address as indication for an outermost frame.

Cc: Steven Rostedt <rostedt@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <redacted>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Indu Bhagat <redacted>
Cc: "Jose E. Marchesi" <redacted>
Cc: Beau Belgrave <redacted>
Cc: Jens Remus <redacted>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Florian Weimer <redacted>
Cc: Sam James <redacted>
Cc: Kees Cook <kees@kernel.org>
Cc: "Carlos O'Donell" <redacted>
Signed-off-by: Jens Remus <redacted>
---

Notes (jremus):
    Changes in v11:
    - New patch. (Jens)

 arch/x86/include/asm/unwind_user.h | 3 ++-
 include/linux/unwind_user_types.h  | 1 +
 kernel/unwind/user.c               | 6 ++++++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h
index 5e0755ea3086..08684bbeff0c 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h

@@ -6,6 +6,7 @@
 	.cfa_off	=  2*(ws),			\
 	.ra_off		= -1*(ws),			\
 	.fp_off		= -2*(ws),			\
-	.use_fp		= true,
+	.use_fp		= true,				\
+	.outermost	= false,
 
 #endif /* _ASM_X86_UNWIND_USER_H */

diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index ee0ce855e045..e07fee69d315 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h

@@ -32,6 +32,7 @@ struct unwind_user_frame {
 	s32 ra_off;
 	s32 fp_off;
 	bool use_fp;
+	bool outermost;
 };
 
 struct unwind_user_state {

diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index f6c543cb255b..c8034a447c16 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c

@@ -33,6 +33,12 @@ static int unwind_user_next_common(struct unwind_user_state *state,
 {
 	unsigned long cfa, fp, ra;
 
+	/* Stop unwinding when reaching an outermost frame. */
+	if (frame->outermost) {
+		state->done = true;
+		return 0;
+	}
+
 	if (frame->use_fp) {
 		if (state->fp < state->sp)
 			return -EINVAL;

-- 
2.48.1