[PATCH v3 2/4] module: Move module_enable_x() and frob_text() in strict_rwx.c

Christophe Leroy
2022-02-22T15:17:45Z

Move module_enable_x() together with module_enable_nx() and
module_enable_ro().

Those three functions are going together, they are all used
to set up the correct page flags on the different sections.

As module_enable_x() is used independently of
CONFIG_STRICT_MODULE_RWX, build strict_rwx.c all the time and
use IS_ENABLED(CONFIG_STRICT_MODULE_RWX) when relevant.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
kernel/module/Makefile | 3 +--
kernel/module/internal.h | 15 +-----------
kernel/module/main.c | 37 -----------------------------
kernel/module/strict_rwx.c | 48 ++++++++++++++++++++++++++++++++++++++
4 files changed, 50 insertions(+), 53 deletions(-)

diff --git a/kernel/module/Makefile b/kernel/module/Makefile
index a46e6361017f..a94f7b8b2740 100644
--- a/kernel/module/Makefile
+++ b/kernel/module/Makefile
@@ -7,12 +7,11 @@
# and produce insane amounts of uninteresting coverage.
KCOV_INSTRUMENT_module.o := n

-obj-y += main.o
+obj-y += main.o strict_rwx.o
obj-$(CONFIG_MODULE_DECOMPRESS) += decompress.o
obj-$(CONFIG_MODULE_SIG) += signing.o
obj-$(CONFIG_LIVEPATCH) += livepatch.o
obj-$(CONFIG_MODULES_TREE_LOOKUP) += tree_lookup.o
-obj-$(CONFIG_STRICT_MODULE_RWX) += strict_rwx.o
obj-$(CONFIG_DEBUG_KMEMLEAK) += debug_kmemleak.o
obj-$(CONFIG_KALLSYMS) += kallsyms.o
obj-$(CONFIG_PROC_FS) += procfs.o
diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index 7178b7c09cdd..276e3f49a4ae 100644
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@@ -182,25 +182,12 @@ static inline struct module *mod_find(unsigned long addr, struct mod_tree_root *
}
#endif /* CONFIG_MODULES_TREE_LOOKUP */

-void frob_text(const struct module_layout *layout, int (*set_memory)(unsigned long start,
- int num_pages));
-
-#ifdef CONFIG_STRICT_MODULE_RWX
void module_enable_ro(const struct module *mod, bool after_init);
void module_enable_nx(const struct module *mod);
+void module_enable_x(const struct module *mod);
int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
char *secstrings, struct module *mod);

-#else /* !CONFIG_STRICT_MODULE_RWX */
-static inline void module_enable_nx(const struct module *mod) { }
-static inline void module_enable_ro(const struct module *mod, bool after_init) {}
-static inline int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
- char *secstrings, struct module *mod)
-{
- return 0;
-}
-#endif /* CONFIG_STRICT_MODULE_RWX */
-
#ifdef CONFIG_MODULE_SIG
int module_sig_check(struct load_info *info, int flags);
#else /* !CONFIG_MODULE_SIG */
diff --git a/kernel/module/main.c b/kernel/module/main.c
index be3b31ba6e16..47addf849ef7 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1142,43 +1142,6 @@ resolve_symbol_wait(struct module *mod,
return ksym;
}

-/*
- * LKM RO/NX protection: protect module's text/ro-data
- * from modification and any data from execution.
- *
- * General layout of module is:
- * [text] [read-only-data] [ro-after-init] [writable data]
- * text_size -----^ ^ ^ ^
- * ro_size ------------------------| | |
- * ro_after_init_size -----------------------------| |
- * size -----------------------------------------------------------|
- *
- * These values are always page-aligned (as is base)
- */
-
-/*
- * Since some arches are moving towards PAGE_KERNEL module allocations instead
- * of PAGE_KERNEL_EXEC, keep frob_text() and module_enable_x() outside of the
- * CONFIG_STRICT_MODULE_RWX block below because they are needed regardless of
- * whether we are strict.
- */
-void frob_text(const struct module_layout *layout,
- int (*set_memory)(unsigned long start, int num_pages))
-{
- set_memory((unsigned long)layout->base,
- PAGE_ALIGN(layout->text_size) >> PAGE_SHIFT);
-}
-
-static void module_enable_x(const struct module *mod)
-{
- if (!PAGE_ALIGNED(mod->core_layout.base) ||
- !PAGE_ALIGNED(mod->init_layout.base))
- return;
-
- frob_text(&mod->core_layout, set_memory_x);
- frob_text(&mod->init_layout, set_memory_x);
-}
-
void __weak module_memfree(void *module_region)
{
/*
diff --git a/kernel/module/strict_rwx.c b/kernel/module/strict_rwx.c
index 1a6b9573260b..6b99be9e88e1 100644
--- a/kernel/module/strict_rwx.c
+++ b/kernel/module/strict_rwx.c
@@ -11,6 +11,34 @@
#include <linux/set_memory.h>
#include "internal.h"

+/*
+ * LKM RO/NX protection: protect module's text/ro-data
+ * from modification and any data from execution.
+ *
+ * General layout of module is:
+ * [text] [read-only-data] [ro-after-init] [writable data]
+ * text_size -----^ ^ ^ ^
+ * ro_size ------------------------| | |
+ * ro_after_init_size -----------------------------| |
+ * size -----------------------------------------------------------|
+ *
+ * These values are always page-aligned (as is base) when
+ * CONFIG_STRICT_MODULE_RWX is set.
+ */
+
+/*
+ * Since some arches are moving towards PAGE_KERNEL module allocations instead
+ * of PAGE_KERNEL_EXEC, keep frob_text() and module_enable_x() independent of
+ * CONFIG_STRICT_MODULE_RWX because they are needed regardless of whether we
+ * are strict.
+ */
+static void frob_text(const struct module_layout *layout,
+ int (*set_memory)(unsigned long start, int num_pages))
+{
+ set_memory((unsigned long)layout->base,
+ PAGE_ALIGN(layout->text_size) >> PAGE_SHIFT);
+}
+
static void frob_rodata(const struct module_layout *layout,
int (*set_memory)(unsigned long start, int num_pages))
{
@@ -41,10 +69,24 @@ static void frob_writable_data(const struct module_layout *layout,
(layout->size - layout->ro_after_init_size) >> PAGE_SHIFT);
}

+void module_enable_x(const struct module *mod)
+{
+ if (!PAGE_ALIGNED(mod->core_layout.base) ||
+ !PAGE_ALIGNED(mod->init_layout.base))
+ return;
+
+ frob_text(&mod->core_layout, set_memory_x);
+ frob_text(&mod->init_layout, set_memory_x);
+}
+
void module_enable_ro(const struct module *mod, bool after_init)
{
+ if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
+ return;
+#ifdef CONFIG_STRICT_MODULE_RWX
if (!rodata_enabled)
return;
+#endif

set_vm_flush_reset_perms(mod->core_layout.base);
set_vm_flush_reset_perms(mod->init_layout.base);
@@ -60,6 +102,9 @@ void module_enable_ro(const struct module *mod, bool after_init)

void module_enable_nx(const struct module *mod)
{
+ if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
+ return;
+
frob_rodata(&mod->data_layout, set_memory_nx);
frob_ro_after_init(&mod->data_layout, set_memory_nx);
frob_writable_data(&mod->data_layout, set_memory_nx);
@@ -73,6 +118,9 @@ int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
const unsigned long shf_wx = SHF_WRITE | SHF_EXECINSTR;
int i;

+ if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
+ return 0;
+
for (i = 0; i < hdr->e_shnum; i++) {
if ((sechdrs[i].sh_flags & shf_wx) == shf_wx) {
pr_err("%s: section %s (index %d) has invalid WRITE|EXEC flags\n",
--
2.34.1