[PATCH v8 06/13] module: Move strict rwx support to a separate file

Aaron Tomlin
2022-02-22T14:13:33Z

No functional change.

This patch migrates code that makes module text
and rodata memory read-only and non-text memory
non-executable from core module code into
kernel/module/strict_rwx.c.

Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
---
kernel/module/Makefile | 1 +
kernel/module/internal.h | 32 ++++++++++++
kernel/module/main.c | 99 +-------------------------------------
kernel/module/strict_rwx.c | 85 ++++++++++++++++++++++++++++++++
4 files changed, 120 insertions(+), 97 deletions(-)
create mode 100644 kernel/module/strict_rwx.c

diff --git a/kernel/module/Makefile b/kernel/module/Makefile
index 88774e386276..d313c8472cb3 100644
--- a/kernel/module/Makefile
+++ b/kernel/module/Makefile
@@ -12,3 +12,4 @@ 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
diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index f1682e3677be..a6895bb5598a 100644
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@@ -20,6 +20,17 @@
/* Maximum number of characters written by module_flags() */
#define MODULE_FLAGS_BUF_SIZE (TAINT_FLAGS_COUNT + 4)

+/*
+ * Modules' sections will be aligned on page boundaries
+ * to ensure complete separation of code and data, but
+ * only when CONFIG_ARCH_HAS_STRICT_MODULE_RWX=y
+ */
+#ifdef CONFIG_ARCH_HAS_STRICT_MODULE_RWX
+# define debug_align(X) PAGE_ALIGN(X)
+#else
+# define debug_align(X) (X)
+#endif
+
extern struct mutex module_mutex;
extern struct list_head modules;

@@ -126,3 +137,24 @@ static inline struct module *mod_find(unsigned long addr)
return NULL;
}
#endif /* CONFIG_MODULES_TREE_LOOKUP */
+
+#ifdef CONFIG_ARCH_HAS_STRICT_MODULE_RWX
+void frob_text(const struct module_layout *layout, int (*set_memory)(unsigned long start,
+ int num_pages));
+#endif /* CONFIG_ARCH_HAS_STRICT_MODULE_RWX */
+
+#ifdef CONFIG_STRICT_MODULE_RWX
+void module_enable_ro(const struct module *mod, bool after_init);
+void module_enable_nx(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 */
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 76b53880ad91..5cd63f14b1ef 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -63,17 +63,6 @@
#define CREATE_TRACE_POINTS
#include <trace/events/module.h>

-/*
- * Modules' sections will be aligned on page boundaries
- * to ensure complete separation of code and data, but
- * only when CONFIG_ARCH_HAS_STRICT_MODULE_RWX=y
- */
-#ifdef CONFIG_ARCH_HAS_STRICT_MODULE_RWX
-# define debug_align(X) ALIGN(X, PAGE_SIZE)
-#else
-# define debug_align(X) (X)
-#endif
-
/*
* Mutex protects:
* 1) List of modules (also safely readable with preempt_disable),
@@ -1819,8 +1808,8 @@ static void mod_sysfs_teardown(struct module *mod)
* whether we are strict.
*/
#ifdef CONFIG_ARCH_HAS_STRICT_MODULE_RWX
-static void frob_text(const struct module_layout *layout,
- int (*set_memory)(unsigned long start, int num_pages))
+void frob_text(const struct module_layout *layout,
+ int (*set_memory)(unsigned long start, int num_pages))
{
BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->text_size & (PAGE_SIZE-1));
@@ -1837,90 +1826,6 @@ static void module_enable_x(const struct module *mod)
static void module_enable_x(const struct module *mod) { }
#endif /* CONFIG_ARCH_HAS_STRICT_MODULE_RWX */

-#ifdef CONFIG_STRICT_MODULE_RWX
-static void frob_rodata(const struct module_layout *layout,
- int (*set_memory)(unsigned long start, int num_pages))
-{
- BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
- BUG_ON((unsigned long)layout->text_size & (PAGE_SIZE-1));
- BUG_ON((unsigned long)layout->ro_size & (PAGE_SIZE-1));
- set_memory((unsigned long)layout->base + layout->text_size,
- (layout->ro_size - layout->text_size) >> PAGE_SHIFT);
-}
-
-static void frob_ro_after_init(const struct module_layout *layout,
- int (*set_memory)(unsigned long start, int num_pages))
-{
- BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
- BUG_ON((unsigned long)layout->ro_size & (PAGE_SIZE-1));
- BUG_ON((unsigned long)layout->ro_after_init_size & (PAGE_SIZE-1));
- set_memory((unsigned long)layout->base + layout->ro_size,
- (layout->ro_after_init_size - layout->ro_size) >> PAGE_SHIFT);
-}
-
-static void frob_writable_data(const struct module_layout *layout,
- int (*set_memory)(unsigned long start, int num_pages))
-{
- BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
- BUG_ON((unsigned long)layout->ro_after_init_size & (PAGE_SIZE-1));
- BUG_ON((unsigned long)layout->size & (PAGE_SIZE-1));
- set_memory((unsigned long)layout->base + layout->ro_after_init_size,
- (layout->size - layout->ro_after_init_size) >> PAGE_SHIFT);
-}
-
-static void module_enable_ro(const struct module *mod, bool after_init)
-{
- if (!rodata_enabled)
- return;
-
- set_vm_flush_reset_perms(mod->core_layout.base);
- set_vm_flush_reset_perms(mod->init_layout.base);
- frob_text(&mod->core_layout, set_memory_ro);
-
- frob_rodata(&mod->core_layout, set_memory_ro);
- frob_text(&mod->init_layout, set_memory_ro);
- frob_rodata(&mod->init_layout, set_memory_ro);
-
- if (after_init)
- frob_ro_after_init(&mod->core_layout, set_memory_ro);
-}
-
-static void module_enable_nx(const struct module *mod)
-{
- frob_rodata(&mod->core_layout, set_memory_nx);
- frob_ro_after_init(&mod->core_layout, set_memory_nx);
- frob_writable_data(&mod->core_layout, set_memory_nx);
- frob_rodata(&mod->init_layout, set_memory_nx);
- frob_writable_data(&mod->init_layout, set_memory_nx);
-}
-
-static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
- char *secstrings, struct module *mod)
-{
- const unsigned long shf_wx = SHF_WRITE|SHF_EXECINSTR;
- int i;
-
- 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",
- mod->name, secstrings + sechdrs[i].sh_name, i);
- return -ENOEXEC;
- }
- }
-
- return 0;
-}
-
-#else /* !CONFIG_STRICT_MODULE_RWX */
-static void module_enable_nx(const struct module *mod) { }
-static void module_enable_ro(const struct module *mod, bool after_init) {}
-static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
- char *secstrings, struct module *mod)
-{
- return 0;
-}
-#endif /* CONFIG_STRICT_MODULE_RWX */
-
void __weak module_memfree(void *module_region)
{
/*
diff --git a/kernel/module/strict_rwx.c b/kernel/module/strict_rwx.c
new file mode 100644
index 000000000000..7949dfd449c2
--- /dev/null
+++ b/kernel/module/strict_rwx.c
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Module strict rwx
+ *
+ * Copyright (C) 2015 Rusty Russell
+ */
+
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/vmalloc.h>
+#include <linux/set_memory.h>
+#include "internal.h"
+
+static void frob_rodata(const struct module_layout *layout,
+ int (*set_memory)(unsigned long start, int num_pages))
+{
+ BUG_ON(!PAGE_ALIGNED(layout->base));
+ BUG_ON(!PAGE_ALIGNED(layout->text_size));
+ BUG_ON(!PAGE_ALIGNED(layout->ro_size));
+ set_memory((unsigned long)layout->base + layout->text_size,
+ (layout->ro_size - layout->text_size) >> PAGE_SHIFT);
+}
+
+static void frob_ro_after_init(const struct module_layout *layout,
+ int (*set_memory)(unsigned long start, int num_pages))
+{
+ BUG_ON(!PAGE_ALIGNED(layout->base));
+ BUG_ON(!PAGE_ALIGNED(layout->ro_size));
+ BUG_ON(!PAGE_ALIGNED(layout->ro_after_init_size));
+ set_memory((unsigned long)layout->base + layout->ro_size,
+ (layout->ro_after_init_size - layout->ro_size) >> PAGE_SHIFT);
+}
+
+static void frob_writable_data(const struct module_layout *layout,
+ int (*set_memory)(unsigned long start, int num_pages))
+{
+ BUG_ON(!PAGE_ALIGNED(layout->base));
+ BUG_ON(!PAGE_ALIGNED(layout->ro_after_init_size));
+ BUG_ON(!PAGE_ALIGNED(layout->size));
+ set_memory((unsigned long)layout->base + layout->ro_after_init_size,
+ (layout->size - layout->ro_after_init_size) >> PAGE_SHIFT);
+}
+
+void module_enable_ro(const struct module *mod, bool after_init)
+{
+ if (!rodata_enabled)
+ return;
+
+ set_vm_flush_reset_perms(mod->core_layout.base);
+ set_vm_flush_reset_perms(mod->init_layout.base);
+ frob_text(&mod->core_layout, set_memory_ro);
+
+ frob_rodata(&mod->core_layout, set_memory_ro);
+ frob_text(&mod->init_layout, set_memory_ro);
+ frob_rodata(&mod->init_layout, set_memory_ro);
+
+ if (after_init)
+ frob_ro_after_init(&mod->core_layout, set_memory_ro);
+}
+
+void module_enable_nx(const struct module *mod)
+{
+ frob_rodata(&mod->core_layout, set_memory_nx);
+ frob_ro_after_init(&mod->core_layout, set_memory_nx);
+ frob_writable_data(&mod->core_layout, set_memory_nx);
+ frob_rodata(&mod->init_layout, set_memory_nx);
+ frob_writable_data(&mod->init_layout, set_memory_nx);
+}
+
+int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
+ char *secstrings, struct module *mod)
+{
+ const unsigned long shf_wx = SHF_WRITE | SHF_EXECINSTR;
+ int i;
+
+ 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",
+ mod->name, secstrings + sechdrs[i].sh_name, i);
+ return -ENOEXEC;
+ }
+ }
+
+ return 0;
+}
--
2.34.1