Commit f7984942 authored by Petr Pavlu's avatar Petr Pavlu
Browse files

module: Add a separate function to mark sections as read-only after init 



Move the logic to mark special sections as read-only after module
initialization into a separate function, along other related code in
strict_rwx.c. Use a table with names of such sections to make it easier to
add more.

Reviewed-by: default avatarSami Tolvanen <samitolvanen@google.com>
Reviewed-by: default avatarLuis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20250306131430.7016-3-petr.pavlu@suse.com


Signed-off-by: default avatarPetr Pavlu <petr.pavlu@suse.com>
parent 7bba3167

kernel/module/internal.h

+2 −0
Original line number Diff line number Diff line
@@ -325,6 +325,8 @@ int module_enable_text_rox(const struct module *mod); 
int module_enforce_rwx_sections(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,

				const char *secstrings,

				const struct module *mod);

void module_mark_ro_after_init(const Elf_Ehdr *hdr, Elf_Shdr *sechdrs,

			       const char *secstrings);



#ifdef CONFIG_MODULE_SIG

int module_sig_check(struct load_info *info, int flags);

kernel/module/main.c

+3 −15
Original line number Diff line number Diff line
@@ -2768,7 +2768,6 @@ core_param(module_blacklist, module_blacklist, charp, 0400); 
static struct module *layout_and_allocate(struct load_info *info, int flags)

{

	struct module *mod;

	unsigned int ndx;

	int err;



	/* Allow arches to frob section contents and sizes.  */
@@ -2786,22 +2785,11 @@ static struct module *layout_and_allocate(struct load_info *info, int flags) 
	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.

	 * Mark relevant sections as SHF_RO_AFTER_INIT so layout_sections() can

	 * put them 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;

	/*

	 * Mark the __jump_table section as ro_after_init as well: these data

	 * structures are never modified, with the exception of entries that

	 * refer to code in the __init section, which are annotated as such

	 * at module load time.

	 */

	ndx = find_sec(info, "__jump_table");

	if (ndx)

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

	module_mark_ro_after_init(info->hdr, info->sechdrs, info->secstrings);



	/*

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

kernel/module/strict_rwx.c

+33 −0
Original line number Diff line number Diff line
@@ -107,3 +107,36 @@ int module_enforce_rwx_sections(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs, 


	return 0;

}



static const char *const ro_after_init[] = {

	/*

	 * Section .data..ro_after_init holds data explicitly annotated by

	 * __ro_after_init.

	 */

	".data..ro_after_init",



	/*

	 * Section __jump_table holds data structures that are never modified,

	 * with the exception of entries that refer to code in the __init

	 * section, which are marked as such at module load time.

	 */

	"__jump_table",

};



void module_mark_ro_after_init(const Elf_Ehdr *hdr, Elf_Shdr *sechdrs,

			       const char *secstrings)

{

	int i, j;



	for (i = 1; i < hdr->e_shnum; i++) {

		Elf_Shdr *shdr = &sechdrs[i];



		for (j = 0; j < ARRAY_SIZE(ro_after_init); j++) {

			if (strcmp(secstrings + shdr->sh_name,

				   ro_after_init[j]) == 0) {

				shdr->sh_flags |= SHF_RO_AFTER_INIT;

				break;

			}

		}

	}

}