linux-kernel - [PATCH v11 10/15] unwind_user/sframe: Add support for outermost frame indication

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Message-ID: <20251022144326.4082059-11-jremus@linux.ibm.com>
Date: Wed, 22 Oct 2025 16:43:21 +0200
From: Jens Remus <jremus@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        bpf@...r.kernel.org, x86@...nel.org, linux-mm@...ck.org,
        Steven Rostedt <rostedt@...nel.org>
Cc: Jens Remus <jremus@...ux.ibm.com>, Josh Poimboeuf <jpoimboe@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrii Nakryiko <andrii@...nel.org>,
        Indu Bhagat <indu.bhagat@...cle.com>,
        "Jose E. Marchesi" <jemarch@....org>,
        Beau Belgrave <beaub@...ux.microsoft.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Florian Weimer <fweimer@...hat.com>, Kees Cook <kees@...nel.org>,
        "Carlos O'Donell" <codonell@...hat.com>, Sam James <sam@...too.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
        Michal Hocko <mhocko@...e.com>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: [PATCH v11 10/15] unwind_user/sframe: Add support for outermost frame indication

SFrame may represent an undefined return address (RA) as SFrame FRE
without any offsets as indication for an outermost frame.

Cc: Steven Rostedt <rostedt@...nel.org>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Andrii Nakryiko <andrii@...nel.org>
Cc: Indu Bhagat <indu.bhagat@...cle.com>
Cc: "Jose E. Marchesi" <jemarch@....org>
Cc: Beau Belgrave <beaub@...ux.microsoft.com>
Cc: Jens Remus <jremus@...ux.ibm.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Florian Weimer <fweimer@...hat.com>
Cc: Sam James <sam@...too.org>
Cc: Kees Cook <kees@...nel.org>
Cc: "Carlos O'Donell" <codonell@...hat.com>
Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
---

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

 kernel/unwind/sframe.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 5536374e2a22..bc3e2eb00325 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -24,6 +24,7 @@ struct sframe_fre {
 	s32		ra_off;
 	s32		fp_off;
 	u8		info;
+	bool		ra_undefined;
 };
 
 DEFINE_STATIC_SRCU(sframe_srcu);
@@ -173,6 +174,7 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	unsigned char offset_count, offset_size;
 	s32 cfa_off, ra_off, fp_off;
 	unsigned long cur = fre_addr;
+	bool ra_undefined = false;
 	unsigned char addr_size;
 	u32 ip_off;
 	u8 info;
@@ -191,7 +193,7 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	UNSAFE_GET_USER_INC(info, cur, 1, Efault);
 	offset_count = SFRAME_FRE_OFFSET_COUNT(info);
 	offset_size  = offset_size_enum_to_size(SFRAME_FRE_OFFSET_SIZE(info));
-	if (!offset_count || !offset_size)
+	if (!offset_size)
 		return -EFAULT;
 
 	if (cur + (offset_count * offset_size) > sec->fres_end)
@@ -199,6 +201,14 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 
 	fre->size = addr_size + 1 + (offset_count * offset_size);
 
+	if (!offset_count) {
+		cfa_off		= 0;
+		ra_off		= 0;
+		fp_off		= 0;
+		ra_undefined	= true;
+		goto done;
+	}
+
 	UNSAFE_GET_USER_INC(cfa_off, cur, offset_size, Efault);
 	offset_count--;
 
@@ -219,11 +229,13 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	if (offset_count)
 		return -EFAULT;
 
+done:
 	fre->ip_off		= ip_off;
 	fre->cfa_off		= cfa_off;
 	fre->ra_off		= ra_off;
 	fre->fp_off		= fp_off;
 	fre->info		= info;
+	fre->ra_undefined	= ra_undefined;
 
 	return 0;
 
@@ -285,6 +297,7 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 	frame->ra_off  = fre->ra_off;
 	frame->fp_off  = fre->fp_off;
 	frame->use_fp  = SFRAME_FRE_CFA_BASE_REG_ID(fre->info) == SFRAME_BASE_REG_FP;
+	frame->outermost = fre->ra_undefined;
 
 	return 0;
 }
-- 
2.48.1