[PATCH v9 10/11] unwind_user/sframe: Add .sframe validation option

[Steven Rostedt <rostedt@kernel.org>]

From: Josh Poimboeuf <jpoimboe@kernel.org>

Add a debug feature to validate all .sframe sections when first loading
the file rather than on demand.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v8: https://lore.kernel.org/20250708021200.223446028@kernel.org

- Add "safe_read_fre()" and "safe_read_fde()" to call their respective
  functions with a user_read_access_begin() wrapper around them so that
  the validator can simply use dbg_sec() directly instead of a _uaccess()
  hacked version.

 arch/Kconfig           | 19 +++++++++
 kernel/unwind/sframe.c | 96 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 115 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index f3b3e5a91f6d..c2f12135db92 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -446,6 +446,25 @@ config HAVE_UNWIND_USER_SFRAME
 	bool
 	select UNWIND_USER
 
+config SFRAME_VALIDATION
+	bool "Enable .sframe section debugging"
+	depends on HAVE_UNWIND_USER_SFRAME
+	depends on DYNAMIC_DEBUG
+	help
+	  When adding an .sframe section for a task, validate the entire
+	  section immediately rather than on demand.
+
+	  This is a debug feature which is helpful for rooting out .sframe
+	  section issues.  If the .sframe section is corrupt, it will fail to
+	  load immediately, with more information provided in dynamic printks.
+
+	  This has a significant page cache footprint due to its reading of the
+	  entire .sframe section for every loaded executable and shared
+	  library.  Also, it's done for all processes, even those which don't
+	  get stack traced by the kernel.  Not recommended for general use.
+
+	  If unsure, say N.
+
 config HAVE_PERF_REGS
 	bool
 	help
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 66d3ba3c8389..79ff3c0fc11f 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -319,6 +319,98 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
 	return ret;
 }
 
+#ifdef CONFIG_SFRAME_VALIDATION
+
+static int safe_read_fde(struct sframe_section *sec,
+			 unsigned int fde_num, struct sframe_fde *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);
+	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_fre *fre)
+{
+	int ret;
+
+	if (!user_read_access_begin((void __user *)sec->sframe_start,
+				    sec->sframe_end - sec->sframe_start))
+		return -EFAULT;
+	ret = __read_fre(sec, fde, fre_addr, fre);
+	user_read_access_end();
+	return ret;
+}
+
+static int sframe_validate_section(struct sframe_section *sec)
+{
+	unsigned long prev_ip = 0;
+	unsigned int i;
+
+	for (i = 0; i < sec->num_fdes; i++) {
+		struct sframe_fre *fre, *prev_fre = NULL;
+		unsigned long ip, fre_addr;
+		struct sframe_fde fde;
+		struct sframe_fre fres[2];
+		bool which = false;
+		unsigned int j;
+		int ret;
+
+		ret = safe_read_fde(sec, i, &fde);
+		if (ret)
+			return ret;
+
+		ip = sec->sframe_start + fde.start_addr;
+		if (ip <= prev_ip) {
+			dbg_sec("fde %u not sorted\n", i);
+			return -EFAULT;
+		}
+		prev_ip = ip;
+
+		fre_addr = sec->fres_start + fde.fres_off;
+		for (j = 0; j < fde.fres_num; j++) {
+			int ret;
+
+			fre = which ? fres : fres + 1;
+			which = !which;
+
+			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,
+					fde.fres_off, fde.fres_num,
+					fde.info, fde.rep_size);
+				return ret;
+			}
+
+			fre_addr += fre->size;
+
+			if (prev_fre && fre->ip_off <= prev_fre->ip_off) {
+				dbg_sec("fde %u: fre %u not sorted\n", i, j);
+				return -EFAULT;
+			}
+
+			prev_fre = fre;
+		}
+	}
+
+	return 0;
+}
+
+#else /*  !CONFIG_SFRAME_VALIDATION */
+
+static int sframe_validate_section(struct sframe_section *sec) { return 0; }
+
+#endif /* !CONFIG_SFRAME_VALIDATION */
+
+
 static void free_section(struct sframe_section *sec)
 {
 	dbg_free(sec);
@@ -427,6 +519,10 @@ int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
 		goto err_free;
 	}
 
+	ret = sframe_validate_section(sec);
+	if (ret)
+		goto err_free;
+
 	ret = mtree_insert_range(sframe_mt, sec->text_start, sec->text_end, sec, GFP_KERNEL);
 	if (ret) {
 		dbg_sec("mtree_insert_range failed: text=%lx-%lx\n",
-- 
2.47.2