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>
---
 arch/Kconfig           | 19 ++++++++++
 kernel/unwind/sframe.c | 81 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 100 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index 12a3b73cbe66..b3676605bab6 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -453,6 +453,25 @@ config HAVE_UNWIND_USER_SFRAME
 config AS_SFRAME
 	def_bool $(as-instr,.cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc)
 
+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 a2ca26b952d3..bba14c5fe0f5 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -336,6 +336,83 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
 	return ret;
 }
 
+#ifdef CONFIG_SFRAME_VALIDATION
+
+static __always_inline 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 = __read_fde(sec, i, &fde);
+		if (ret)
+			return ret;
+
+		ip = sec->sframe_start + fde.start_addr;
+		if (ip <= prev_ip) {
+			dbg_sec_uaccess("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 = __read_fre(sec, &fde, fre_addr, fre);
+			if (ret) {
+				dbg_sec_uaccess("fde %u: __read_fre(%u) failed\n", i, j);
+				dbg_print_fde_uaccess(sec, &fde);
+				return ret;
+			}
+
+			fre_addr += fre->size;
+
+			if (prev_fre && fre->ip_off <= prev_fre->ip_off) {
+				dbg_sec_uaccess("fde %u: fre %u not sorted\n", i, j);
+				return -EFAULT;
+			}
+
+			prev_fre = fre;
+		}
+	}
+
+	return 0;
+}
+
+static int sframe_validate_section(struct sframe_section *sec)
+{
+	int ret;
+
+	if (!user_read_access_begin((void __user *)sec->sframe_start,
+				    sec->sframe_end - sec->sframe_start)) {
+		dbg_sec("section usercopy failed\n");
+		return -EFAULT;
+	}
+
+	ret = __sframe_validate_section(sec);
+	user_read_access_end();
+	return ret;
+}
+
+#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);
@@ -444,6 +521,10 @@ 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",
-- 
2.48.1