linux-kernel - [RFC PATCH 2/2] fixup! unwind_user/sframe: Add .sframe validation option

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Message-ID: <20251023160545.549532-2-jremus@linux.ibm.com>
Date: Thu, 23 Oct 2025 18:05:45 +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: [RFC PATCH 2/2] fixup! unwind_user/sframe: Add .sframe validation option

This RFC fixup is POC to demonstrate how the SFrame validation code
would adjust if introducing an internal FDE representation (struct
sframe_fde_internal) similar to the used internal FRE representation
(struct sframe_fre) in the SFrame reading code.  The goal is to
eliminate the passing through of fde_start_base in many places as well
as the various computations of the effective function start address
(= *fde_start_base + fde->start_addr) throughout this module.  The
internal FDE representation simply conveys the effective function start
address via the "unsigned long func_start_addr" field.

Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
---
 kernel/unwind/sframe.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index f88fc2c92c58..f2977c010117 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -354,21 +354,21 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
 #ifdef CONFIG_SFRAME_VALIDATION
 
 static int safe_read_fde(struct sframe_section *sec,
-			 unsigned int fde_num, struct sframe_fde *fde,
-			 unsigned long *fde_start_base)
+			 unsigned int fde_num, struct sframe_fde_internal *fde)
 {
 	int ret;
 
 	if (!user_read_access_begin((void __user *)sec->sframe_start,
 				    sec->sframe_end - sec->sframe_start))
 		return -EFAULT;
-	ret = __read_fde(sec, fde_num, fde, fde_start_base);
+	ret = __read_fde(sec, fde_num, fde);
 	user_read_access_end();
 	return ret;
 }
 
 static int safe_read_fre(struct sframe_section *sec,
-			 struct sframe_fde *fde, unsigned long fre_addr,
+			 struct sframe_fde_internal *fde,
+			 unsigned long fre_addr,
 			 struct sframe_fre *fre)
 {
 	int ret;
@@ -388,18 +388,18 @@ static int sframe_validate_section(struct sframe_section *sec)
 
 	for (i = 0; i < sec->num_fdes; i++) {
 		struct sframe_fre *fre, *prev_fre = NULL;
-		unsigned long ip, fde_start_base, fre_addr;
-		struct sframe_fde fde;
+		unsigned long ip, fre_addr;
+		struct sframe_fde_internal fde;
 		struct sframe_fre fres[2];
 		bool which = false;
 		unsigned int j;
 		int ret;
 
-		ret = safe_read_fde(sec, i, &fde, &fde_start_base);
+		ret = safe_read_fde(sec, i, &fde);
 		if (ret)
 			return ret;
 
-		ip = fde_start_base + fde.start_addr;
+		ip = fde.func_start_addr;
 		if (ip <= prev_ip) {
 			dbg_sec("fde %u not sorted\n", i);
 			return -EFAULT;
@@ -416,8 +416,8 @@ static int sframe_validate_section(struct sframe_section *sec)
 			ret = safe_read_fre(sec, &fde, fre_addr, fre);
 			if (ret) {
 				dbg_sec("fde %u: __read_fre(%u) failed\n", i, j);
-				dbg_sec("FDE: start_addr:0x%x func_size:0x%x fres_off:0x%x fres_num:%d info:%u rep_size:%u\n",
-					fde.start_addr, fde.func_size,
+				dbg_sec("FDE: func_start_addr:0x%lx func_size:0x%x fres_off:0x%x fres_num:%d info:%u rep_size:%u\n",
+					fde.func_start_addr, fde.func_size,
 					fde.fres_off, fde.fres_num,
 					fde.info, fde.rep_size);
 				return ret;
-- 
2.48.1