[PATCH v4 27/39] unwind_user/sframe: Add .sframe validation option

Josh Poimboeuf
2025-01-22T02:32:20Z

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