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Commit 444d13ff authored by Jessica Yu's avatar Jessica Yu Committed by Rusty Russell
Browse files

modules: add ro_after_init support 



Add ro_after_init support for modules by adding a new page-aligned section
in the module layout (after rodata) for ro_after_init data and enabling RO
protection for that section after module init runs.

Signed-off-by: default avatarJessica Yu <jeyu@redhat.com>
Acked-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent bdc9f373

include/linux/module.h

+4 −2
Original line number Diff line number Diff line
@@ -298,6 +298,8 @@ struct module_layout { 
	unsigned int text_size;

	/* Size of RO section of the module (text+rodata) */

	unsigned int ro_size;

	/* Size of RO after init section */

	unsigned int ro_after_init_size;



#ifdef CONFIG_MODULES_TREE_LOOKUP

	struct mod_tree_node mtn;
@@ -765,12 +767,12 @@ extern int module_sysfs_initialized; 
#ifdef CONFIG_DEBUG_SET_MODULE_RONX

extern void set_all_modules_text_rw(void);

extern void set_all_modules_text_ro(void);

extern void module_enable_ro(const struct module *mod);

extern void module_enable_ro(const struct module *mod, bool after_init);

extern void module_disable_ro(const struct module *mod);

#else

static inline void set_all_modules_text_rw(void) { }

static inline void set_all_modules_text_ro(void) { }

static inline void module_enable_ro(const struct module *mod) { }

static inline void module_enable_ro(const struct module *mod, bool after_init) { }

static inline void module_disable_ro(const struct module *mod) { }

#endif

include/uapi/linux/elf.h

+1 −0
Original line number Diff line number Diff line
@@ -286,6 +286,7 @@ typedef struct elf64_phdr { 
#define SHF_ALLOC		0x2

#define SHF_EXECINSTR		0x4

#define SHF_RELA_LIVEPATCH	0x00100000

#define SHF_RO_AFTER_INIT	0x00200000

#define SHF_MASKPROC		0xf0000000



/* special section indexes */

kernel/livepatch/core.c

+1 −1
Original line number Diff line number Diff line
@@ -309,7 +309,7 @@ static int klp_write_object_relocations(struct module *pmod, 
			break;

	}



	module_enable_ro(pmod);

	module_enable_ro(pmod, true);

	return ret;

}

kernel/module.c

+54 −12
Original line number Diff line number Diff line
@@ -1857,10 +1857,11 @@ static void mod_sysfs_teardown(struct module *mod) 
 * from modification and any data from execution.

 *

 * General layout of module is:

 *          [text] [read-only-data] [writable data]

 * text_size -----^                ^               ^

 * ro_size ------------------------|               |

 * size -------------------------------------------|

 *          [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)

 */
@@ -1883,14 +1884,24 @@ static void frob_rodata(const struct module_layout *layout, 
		   (layout->ro_size - layout->text_size) >> PAGE_SHIFT);

}



static void frob_writable_data(const struct module_layout *layout,

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->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->size - layout->ro_size) >> PAGE_SHIFT);

		   (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);

}



/* livepatching wants to disable read-only so it can frob module. */
@@ -1898,21 +1909,26 @@ void module_disable_ro(const struct module *mod) 
{

	frob_text(&mod->core_layout, set_memory_rw);

	frob_rodata(&mod->core_layout, set_memory_rw);

	frob_ro_after_init(&mod->core_layout, set_memory_rw);

	frob_text(&mod->init_layout, set_memory_rw);

	frob_rodata(&mod->init_layout, set_memory_rw);

}



void module_enable_ro(const struct module *mod)

void module_enable_ro(const struct module *mod, bool after_init)

{

	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);
@@ -1921,6 +1937,7 @@ static void module_enable_nx(const struct module *mod) 
static void module_disable_nx(const struct module *mod)

{

	frob_rodata(&mod->core_layout, set_memory_x);

	frob_ro_after_init(&mod->core_layout, set_memory_x);

	frob_writable_data(&mod->core_layout, set_memory_x);

	frob_rodata(&mod->init_layout, set_memory_x);

	frob_writable_data(&mod->init_layout, set_memory_x);
@@ -1963,6 +1980,8 @@ static void disable_ro_nx(const struct module_layout *layout) 
	frob_text(layout, set_memory_rw);

	frob_rodata(layout, set_memory_rw);

	frob_rodata(layout, set_memory_x);

	frob_ro_after_init(layout, set_memory_rw);

	frob_ro_after_init(layout, set_memory_x);

	frob_writable_data(layout, set_memory_x);

}
@@ -2305,6 +2324,7 @@ static void layout_sections(struct module *mod, struct load_info *info) 
		 * finder in the two loops below */

		{ SHF_EXECINSTR | SHF_ALLOC, ARCH_SHF_SMALL },

		{ SHF_ALLOC, SHF_WRITE | ARCH_SHF_SMALL },

		{ SHF_RO_AFTER_INIT | SHF_ALLOC, ARCH_SHF_SMALL },

		{ SHF_WRITE | SHF_ALLOC, ARCH_SHF_SMALL },

		{ ARCH_SHF_SMALL | SHF_ALLOC, 0 }

	};
@@ -2336,7 +2356,11 @@ static void layout_sections(struct module *mod, struct load_info *info) 
			mod->core_layout.size = debug_align(mod->core_layout.size);

			mod->core_layout.ro_size = mod->core_layout.size;

			break;

		case 3: /* whole core */

		case 2: /* RO after init */

			mod->core_layout.size = debug_align(mod->core_layout.size);

			mod->core_layout.ro_after_init_size = mod->core_layout.size;

			break;

		case 4: /* whole core */

			mod->core_layout.size = debug_align(mod->core_layout.size);

			break;

		}
@@ -2366,7 +2390,14 @@ static void layout_sections(struct module *mod, struct load_info *info) 
			mod->init_layout.size = debug_align(mod->init_layout.size);

			mod->init_layout.ro_size = mod->init_layout.size;

			break;

		case 3: /* whole init */

		case 2:

			/*

			 * RO after init doesn't apply to init_layout (only

			 * core_layout), so it just takes the value of ro_size.

			 */

			mod->init_layout.ro_after_init_size = mod->init_layout.ro_size;

			break;

		case 4: /* whole init */

			mod->init_layout.size = debug_align(mod->init_layout.size);

			break;

		}
@@ -3193,6 +3224,7 @@ static struct module *layout_and_allocate(struct load_info *info, int flags) 
{

	/* Module within temporary copy. */

	struct module *mod;

	unsigned int ndx;

	int err;



	mod = setup_load_info(info, flags);
@@ -3215,6 +3247,15 @@ static struct module *layout_and_allocate(struct load_info *info, int flags) 
	/* We will do a special allocation for per-cpu sections later. */

	info->sechdrs[info->index.pcpu].sh_flags &= ~(unsigned long)SHF_ALLOC;



	/*

	 * Mark ro_after_init section with SHF_RO_AFTER_INIT so that

	 * layout_sections() can put it in the right place.

	 * Note: ro_after_init sections also have SHF_{WRITE,ALLOC} set.

	 */

	ndx = find_sec(info, ".data..ro_after_init");

	if (ndx)

		info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT;



	/* Determine total sizes, and put offsets in sh_entsize.  For now

	   this is done generically; there doesn't appear to be any

	   special cases for the architectures. */
@@ -3381,12 +3422,14 @@ static noinline int do_init_module(struct module *mod) 
	/* Switch to core kallsyms now init is done: kallsyms may be walking! */

	rcu_assign_pointer(mod->kallsyms, &mod->core_kallsyms);

#endif

	module_enable_ro(mod, true);

	mod_tree_remove_init(mod);

	disable_ro_nx(&mod->init_layout);

	module_arch_freeing_init(mod);

	mod->init_layout.base = NULL;

	mod->init_layout.size = 0;

	mod->init_layout.ro_size = 0;

	mod->init_layout.ro_after_init_size = 0;

	mod->init_layout.text_size = 0;

	/*

	 * We want to free module_init, but be aware that kallsyms may be
@@ -3478,8 +3521,7 @@ static int complete_formation(struct module *mod, struct load_info *info) 
	/* This relies on module_mutex for list integrity. */

	module_bug_finalize(info->hdr, info->sechdrs, mod);



	/* Set RO and NX regions */

	module_enable_ro(mod);

	module_enable_ro(mod, false);

	module_enable_nx(mod);



	/* Mark state as coming so strong_try_module_get() ignores us,