[PATCH v2] arm64/module: use mod->klp_info section header information for livepatch modules

[Jessica Yu]

The arm64 module loader keeps a pointer into info->sechdrs to keep track
of section header information for .plt section(s). A pointer to the
relevent section header (struct elf64_shdr) in info->sechdrs is stored
in mod->arch.{init,core}.plt. This pointer may be accessed while
applying relocations in apply_relocate_add() for example. And unlike
normal modules, livepatch modules can call apply_relocate_add() after
module load. But the info struct (and therefore info->sechdrs) gets
freed at the end of load_module() and so mod->arch.{init,core}.plt
becomes an invalid pointer after the module is done loading.

Luckily, livepatch modules already keep a copy of Elf section header
information in mod->klp_info. So make sure livepatch modules on arm64
have access to the section headers in klp_info and set
mod->arch.{init,core}.plt to the appropriate section header in
mod->klp_info so that they can call apply_relocate_add() even after
module load.

Signed-off-by: Jessica Yu <jeyu@xxxxxxxxxx>
---

v2:
 - fix missing free_module_elf() in error path
 - move copy_module_elf() and module_finalize() out of post_relocation()
   to make error handling more clear
 - add braces to if-else block in arm64 module_frob_arch_sections()

arch/arm64/include/asm/module.h |  1 +
arch/arm64/kernel/module-plts.c | 17 ++++++++++++-----
arch/arm64/kernel/module.c      | 10 ++++++++++
kernel/module.c                 | 29 +++++++++++++++--------------
4 files changed, 38 insertions(+), 19 deletions(-)

diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/module.h
index fef773c94e9d..ac9b97f9ae5e 100644
--- a/arch/arm64/include/asm/module.h
+++ b/arch/arm64/include/asm/module.h
@@ -25,6 +25,7 @@ struct mod_plt_sec {
	struct elf64_shdr	*plt;
	int			plt_num_entries;
	int			plt_max_entries;
+	int			plt_shndx;
};

struct mod_arch_specific {
diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c
index f0690c2ca3e0..851311ffd427 100644
--- a/arch/arm64/kernel/module-plts.c
+++ b/arch/arm64/kernel/module-plts.c
@@ -210,16 +210,23 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
	 * entries. Record the symtab address as well.
	 */
	for (i = 0; i < ehdr->e_shnum; i++) {
-		if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt"))
+		if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt")) {
			mod->arch.core.plt = sechdrs + i;
-		else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt"))
+			/*
+			 * Keep the section index for the .plt section for
+			 * livepatching. Note that .init.plt is irrelevant to
+			 * livepatch, so only the shndx for .plt is saved.
+			 */
+			mod->arch.core.plt_shndx = i;
+		} else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt")) {
			mod->arch.init.plt = sechdrs + i;
-		else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) &&
+		} else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) &&
			 !strcmp(secstrings + sechdrs[i].sh_name,
-				 ".text.ftrace_trampoline"))
+				 ".text.ftrace_trampoline")) {
			tramp = sechdrs + i;
-		else if (sechdrs[i].sh_type == SHT_SYMTAB)
+		} else if (sechdrs[i].sh_type == SHT_SYMTAB) {
			syms = (Elf64_Sym *)sechdrs[i].sh_addr;
+		}
	}

	if (!mod->arch.core.plt || !mod->arch.init.plt) {
diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
index dd23655fda3a..490e56070a7e 100644
--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c
@@ -461,5 +461,15 @@ int module_finalize(const Elf_Ehdr *hdr,
#endif
	}

+#ifdef CONFIG_LIVEPATCH
+	/*
+	 * For livepatching, switch to the saved section header info for .plt
+	 * stored in mod->klp_info. This is needed so that livepatch is able to
+	 * call apply_relocate_add() after patch module load.
+	 */
+	if (is_livepatch_module(me))
+		me->arch.core.plt = me->klp_info->sechdrs + me->arch.core.plt_shndx;
+#endif
+
	return 0;
}
diff --git a/kernel/module.c b/kernel/module.c
index f475f30eed8c..611f4fe64370 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3365,7 +3365,7 @@ int __weak module_finalize(const Elf_Ehdr *hdr,
	return 0;
}

-static int post_relocation(struct module *mod, const struct load_info *info)
+static void post_relocation(struct module *mod, const struct load_info *info)
{
	/* Sort exception table now relocations are done. */
	sort_extable(mod->extable, mod->extable + mod->num_exentries);
@@ -3376,9 +3376,6 @@ static int post_relocation(struct module *mod, const struct load_info *info)

	/* Setup kallsyms-specific fields. */
	add_kallsyms(mod, info);
-
-	/* Arch-specific module finalizing. */
-	return module_finalize(info->hdr, info->sechdrs, mod);
}

/* Is this module of this name done loading?  No locks held. */
@@ -3726,9 +3723,18 @@ static int load_module(struct load_info *info, const char __user *uargs,
	if (err < 0)
		goto free_modinfo;

-	err = post_relocation(mod, info);
+	post_relocation(mod, info);
+
+	if (is_livepatch_module(mod)) {
+		err = copy_module_elf(mod, info);
+		if (err < 0)
+			goto free_modinfo;
+	}
+
+	/* Arch-specific module finalizing. */
+	err = module_finalize(info->hdr, info->sechdrs, mod);
	if (err < 0)
-		goto free_modinfo;
+		goto free_module_elf;

	flush_module_icache(mod);

@@ -3770,12 +3776,6 @@ static int load_module(struct load_info *info, const char __user *uargs,
	if (err < 0)
		goto coming_cleanup;

-	if (is_livepatch_module(mod)) {
-		err = copy_module_elf(mod, info);
-		if (err < 0)
-			goto sysfs_cleanup;
-	}
-
	/* Get rid of temporary copy. */
	free_copy(info);

@@ -3784,8 +3784,6 @@ static int load_module(struct load_info *info, const char __user *uargs,

	return do_init_module(mod);

- sysfs_cleanup:
-	mod_sysfs_teardown(mod);
 coming_cleanup:
	mod->state = MODULE_STATE_GOING;
	destroy_params(mod->kp, mod->num_kp);
@@ -3809,6 +3807,9 @@ static int load_module(struct load_info *info, const char __user *uargs,
	kfree(mod->args);
 free_arch_cleanup:
	module_arch_cleanup(mod);
+ free_module_elf:
+	if (is_livepatch_module(mod))
+		free_module_elf(mod);
 free_modinfo:
	free_modinfo(mod);
 free_unload:
--
2.16.4