[PATCH v8 08/11] sframe: Add .sframe validation option

[Dylan Hatch]

From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

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

[ Jens Remus: Add support for SFrame V3.  Add support for PC-relative
FDE function start offset.  Adjust to rename of struct sframe_fre to
sframe_fre_internal.  Use %#x/%#lx format specifiers. ]

[ Dylan Hatch: Adapt this patch for in-kernel sframe sections. ]

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Reviewed-by: Indu Bhagat <ibhagatgnu@xxxxxxxxx>
Co-developed-by: Jens Remus <jremus@xxxxxxxxxxxxx>
Signed-off-by: Jens Remus <jremus@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Co-developed-by: Dylan Hatch <dylanbhatch@xxxxxxxxxx>
Signed-off-by: Dylan Hatch <dylanbhatch@xxxxxxxxxx>
---
 arch/Kconfig           | 18 ++++++++++
 kernel/unwind/sframe.c | 78 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 96 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index cc59a5da80915..20aa63c93a0e2 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -538,6 +538,24 @@ config HAVE_UNWIND_KERNEL_SFRAME
 	  practice, this can provide more reliable stacktrace results than
 	  unwinding with frame pointers alone.
 
+config SFRAME_VALIDATION
+	bool "Enable .sframe section debugging"
+	depends on UNWIND_SFRAME_LOOKUP
+	depends on DYNAMIC_DEBUG
+	help
+	  When adding an .sframe section for an object, 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 module.  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 2e8ff783de7d8..62c22ca70614a 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -15,6 +15,7 @@
 #include <linux/kallsyms.h>
 #include <asm/kprobes.h>
 #include <asm/sections.h>
+#include <asm/unwind_sframe.h>
 
 #include "sframe.h"
 #include "sframe_debug.h"
@@ -503,6 +504,73 @@ noinstr int sframe_find(unsigned long ip, struct unwind_frame *frame)
 }
 NOKPROBE_SYMBOL(sframe_find);
 
+#ifdef CONFIG_SFRAME_VALIDATION
+
+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_internal *fre, *prev_fre = NULL;
+		unsigned long ip, fre_addr;
+		struct sframe_fde_internal fde;
+		struct sframe_fre_internal fres[2];
+		bool which = false;
+		unsigned int j;
+		int ret;
+
+		ret = __read_fde(sec, i, &fde);
+		if (ret) {
+			dbg_sec(sec, "__read_fde(%u) failed\n", i);
+			return ret;
+		}
+
+		ip = fde.func_addr;
+		if (ip <= prev_ip) {
+			dbg_sec(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 = __read_fre(sec, &fde, fre_addr, fre);
+			if (ret) {
+				dbg_sec(sec, "FDE %u: __read_fre(%u) failed\n", i, j);
+				return ret;
+			}
+			ret = __read_fre_datawords(sec, &fde, fre);
+			if (ret) {
+				dbg_sec(sec, "FDE %u: __read_fre_datawords(%u) failed\n", i, j);
+				return ret;
+			}
+
+			fre_addr += fre->size;
+
+			if (prev_fre && fre->ip_off <= prev_fre->ip_off) {
+				dbg_sec(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 int sframe_read_header(struct sframe_section *sec)
 {
 	unsigned long header_end, fdes_start, fdes_end, fres_start, fres_end;
@@ -564,6 +632,11 @@ void __init init_sframe_table(void)
 		return;
 	}
 
+	if (sframe_validate_section(&kernel_sfsec)) {
+		pr_warn("invalid vmlinux SFrame section\n");
+		return;
+	}
+
 	sframe_init = true;
 	dbg_print_header(&kernel_sfsec);
 }
@@ -624,6 +697,11 @@ void sframe_module_init(struct module *mod, void *addr, unsigned int size)
 	}
 	sframe_sort_fdes(sec);
 
+	if (sframe_validate_section(sec)) {
+		pr_warn("invalid SFrame section in module %s\n", mod->name);
+		return;
+	}
+
 	/* Ensure SFrame is initialized when sframe_find() happens */
 	smp_store_release(&mod->sframe_init, true);
 	dbg_print_header(sec);
-- 
2.56.0.360.g66cac248cb-goog