[PATCH v2 1/2] arch: arm64: Fail module loading if dynamic SCS patching fails

Adrian Barnaś
2025-09-22T13:04:54Z

Disallow a module to load if SCS dynamic patching fails for its code. For
module loading, instead of running a dry-run to check for patching errors,
try to run patching in the first run and propagate any errors so module
loading will fail.

Signed-off-by: Adrian Barnaś <abarnas@google.com>
---
arch/arm64/include/asm/scs.h | 2 +-
arch/arm64/kernel/module.c | 12 ++++++++++--
arch/arm64/kernel/pi/map_kernel.c | 2 +-
arch/arm64/kernel/pi/patch-scs.c | 10 ++++++----
arch/arm64/kernel/pi/pi.h | 2 +-
5 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/include/asm/scs.h b/arch/arm64/include/asm/scs.h
index a76f9b387a26..c59f6324f2bb 100644
--- a/arch/arm64/include/asm/scs.h
+++ b/arch/arm64/include/asm/scs.h
@@ -53,7 +53,7 @@ enum {
EDYNSCS_INVALID_CFA_OPCODE = 4,
};

-int __pi_scs_patch(const u8 eh_frame[], int size);
+int __pi_scs_patch(const u8 eh_frame[], int size, bool skip_dry_run);

#endif /* __ASSEMBLY __ */

diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
index 40148d2725ce..d32ab7dd86a8 100644
--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c
@@ -484,10 +484,18 @@ int module_finalize(const Elf_Ehdr *hdr,
if (scs_is_dynamic()) {
s = find_section(hdr, sechdrs, ".init.eh_frame");
if (s) {
- ret = __pi_scs_patch((void *)s->sh_addr, s->sh_size);
- if (ret)
+ /*
+ * Because we can reject modules that are malformed
+ * so SCS patching fails, skip dry run and try to patch
+ * it in place. If patching fails, the module would not
+ * be loaded anyway.
+ */
+ ret = __pi_scs_patch((void *)s->sh_addr, s->sh_size, true);
+ if (ret) {
pr_err("module %s: error occurred during dynamic SCS patching (%d)\n",
me->name, ret);
+ return -ENOEXEC;
+ }
}
}

diff --git a/arch/arm64/kernel/pi/map_kernel.c b/arch/arm64/kernel/pi/map_kernel.c
index 0f4bd7771859..7187eda9e8a5 100644
--- a/arch/arm64/kernel/pi/map_kernel.c
+++ b/arch/arm64/kernel/pi/map_kernel.c
@@ -98,7 +98,7 @@ static void __init map_kernel(u64 kaslr_offset, u64 va_offset, int root_level)

if (enable_scs) {
scs_patch(__eh_frame_start + va_offset,
- __eh_frame_end - __eh_frame_start);
+ __eh_frame_end - __eh_frame_start, false);
asm("ic ialluis");

dynamic_scs_is_enabled = true;
diff --git a/arch/arm64/kernel/pi/patch-scs.c b/arch/arm64/kernel/pi/patch-scs.c
index 55d0cd64ef71..bbe7d30ed12b 100644
--- a/arch/arm64/kernel/pi/patch-scs.c
+++ b/arch/arm64/kernel/pi/patch-scs.c
@@ -225,7 +225,7 @@ static int scs_handle_fde_frame(const struct eh_frame *frame,
return 0;
}

-int scs_patch(const u8 eh_frame[], int size)
+int scs_patch(const u8 eh_frame[], int size, bool skip_dry_run)
{
int code_alignment_factor = 1;
bool fde_use_sdata8 = false;
@@ -277,11 +277,13 @@ int scs_patch(const u8 eh_frame[], int size)
}
} else {
ret = scs_handle_fde_frame(frame, code_alignment_factor,
- fde_use_sdata8, true);
+ fde_use_sdata8, !skip_dry_run);
if (ret)
return ret;
- scs_handle_fde_frame(frame, code_alignment_factor,
- fde_use_sdata8, false);
+
+ if (!skip_dry_run)
+ scs_handle_fde_frame(frame, code_alignment_factor,
+ fde_use_sdata8, false);
}

p += sizeof(frame->size) + frame->size;
diff --git a/arch/arm64/kernel/pi/pi.h b/arch/arm64/kernel/pi/pi.h
index 46cafee7829f..220da972cce1 100644
--- a/arch/arm64/kernel/pi/pi.h
+++ b/arch/arm64/kernel/pi/pi.h
@@ -27,7 +27,7 @@ extern pgd_t init_pg_dir[], init_pg_end[];
void init_feature_override(u64 boot_status, const void *fdt, int chosen);
u64 kaslr_early_init(void *fdt, int chosen);
void relocate_kernel(u64 offset);
-int scs_patch(const u8 eh_frame[], int size);
+int scs_patch(const u8 eh_frame[], int size, bool skip_dry_run);

void map_range(u64 *pgd, u64 start, u64 end, u64 pa, pgprot_t prot,
int level, pte_t *tbl, bool may_use_cont, u64 va_offset);
--
2.51.0.534.gc79095c0ca-goog