[RFC PATCH 44/56] x86/module: Update alternatives

David Kaplan
2025-10-13T14:36:22Z

Support resetting and re-configuring retpolines, returns, callthunks,
and alternatives for modules. The ELF information is kept from when the
module was first loaded. Static calls are non-arch specific and handled
in the generic module code.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
arch/x86/include/asm/module.h | 4 +++
arch/x86/kernel/module.c | 58 +++++++++++++++++++++++++++++++++++
2 files changed, 62 insertions(+)

diff --git a/arch/x86/include/asm/module.h b/arch/x86/include/asm/module.h
index 58d7f1017a14..f72359b5120d 100644
--- a/arch/x86/include/asm/module.h
+++ b/arch/x86/include/asm/module.h
@@ -27,4 +27,8 @@ struct mod_arch_specific {
#endif
};

+#ifdef CONFIG_DYNAMIC_MITIGATIONS
+void arch_module_update_alternatives(struct module *mod);
+#endif
+
#endif /* _ASM_X86_MODULE_H */
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index 0765d2360a33..b6beb2b3469c 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -333,3 +333,61 @@ void module_arch_cleanup(struct module *mod)
alternatives_smp_module_del(mod);
its_free_mod(mod);
}
+
+#ifdef CONFIG_DYNAMIC_MITIGATIONS
+void arch_module_update_alternatives(struct module *mod)
+{
+ const Elf_Ehdr *hdr;
+ const Elf_Shdr *sechdrs;
+ const Elf_Shdr *s, *alt = NULL, *retpolines = NULL, *returns = NULL, *calls = NULL;
+ char *secstrings;
+
+ if (!mod->klp_info) {
+ pr_warn("No module livepatch info, unable to update alternatives\n");
+ return;
+ }
+
+ hdr = &mod->klp_info->hdr;
+ sechdrs = mod->klp_info->sechdrs;
+ secstrings = mod->klp_info->secstrings;
+
+ for (s = sechdrs; s < sechdrs + hdr->e_shnum; s++) {
+ if (!strcmp(".altinstructions", secstrings + s->sh_name))
+ alt = s;
+ if (!strcmp(".retpoline_sites", secstrings + s->sh_name))
+ retpolines = s;
+ if (!strcmp(".return_sites", secstrings + s->sh_name))
+ returns = s;
+ if (!strcmp(".call_sites", secstrings + s->sh_name))
+ calls = s;
+ }
+
+ if (retpolines) {
+ void *rseg = (void *)retpolines->sh_addr;
+
+ reset_retpolines(rseg, rseg + retpolines->sh_size, mod);
+ apply_retpolines(rseg, rseg + retpolines->sh_size, mod);
+ }
+ if (returns) {
+ void *rseg = (void *)returns->sh_addr;
+
+ reset_returns(rseg, rseg + returns->sh_size, mod);
+ apply_returns(rseg, rseg + returns->sh_size, mod);
+ }
+ if (calls) {
+ struct callthunk_sites cs = {};
+
+ cs.call_start = (void *)calls->sh_addr;
+ cs.call_end = (void *)calls->sh_addr + calls->sh_size;
+
+ reset_module_callthunks(&cs, mod);
+ callthunks_patch_module_calls(&cs, mod);
+ }
+ if (alt) {
+ void *aseg = (void *)alt->sh_addr;
+
+ reset_alternatives(aseg, aseg + alt->sh_size, mod);
+ apply_alternatives(aseg, aseg + alt->sh_size, mod);
+ }
+}
+#endif
--
2.34.1