Commit 0be41a93 authored by Matthew Maurer's avatar Matthew Maurer Committed by Luis Chamberlain
Browse files

module: Factor out elf_validity_cache_index_mod 



Centralize .gnu.linkonce.this_module detection and property validation.

Signed-off-by: default avatarMatthew Maurer <mmaurer@google.com>
Reviewed-by: default avatarSami Tolvanen <samitolvanen@google.com>
Signed-off-by: default avatarLuis Chamberlain <mcgrof@kernel.org>
parent fbc0e4e4

kernel/module/main.c

+67 −62
Original line number Diff line number Diff line
@@ -1919,6 +1919,68 @@ static int elf_validity_cache_index_info(struct load_info *info) 
	return 0;

}



/**

 * elf_validity_cache_index_mod() - Validates and caches this_module section

 * @info: Load info to cache this_module on.

 *        Must have &load_info->sechdrs and &load_info->secstrings populated

 *

 * The ".gnu.linkonce.this_module" ELF section is special. It is what modpost

 * uses to refer to __this_module and let's use rely on THIS_MODULE to point

 * to &__this_module properly. The kernel's modpost declares it on each

 * modules's *.mod.c file. If the struct module of the kernel changes a full

 * kernel rebuild is required.

 *

 * We have a few expectations for this special section, this function

 * validates all this for us:

 *

 * * The section has contents

 * * The section is unique

 * * We expect the kernel to always have to allocate it: SHF_ALLOC

 * * The section size must match the kernel's run time's struct module

 *   size

 *

 * If all checks pass, the index will be cached in &load_info->index.mod

 *

 * Return: %0 on validation success, %-ENOEXEC on failure

 */

static int elf_validity_cache_index_mod(struct load_info *info)

{

	Elf_Shdr *shdr;

	int mod_idx;



	mod_idx = find_any_unique_sec(info, ".gnu.linkonce.this_module");

	if (mod_idx <= 0) {

		pr_err("module %s: Exactly one .gnu.linkonce.this_module section must exist.\n",

		       info->name ?: "(missing .modinfo section or name field)");

		return -ENOEXEC;

	}



	shdr = &info->sechdrs[mod_idx];



	if (shdr->sh_type == SHT_NOBITS) {

		pr_err("module %s: .gnu.linkonce.this_module section must have a size set\n",

		       info->name ?: "(missing .modinfo section or name field)");

		return -ENOEXEC;

	}



	if (!(shdr->sh_flags & SHF_ALLOC)) {

		pr_err("module %s: .gnu.linkonce.this_module must occupy memory during process execution\n",

		       info->name ?: "(missing .modinfo section or name field)");

		return -ENOEXEC;

	}



	if (shdr->sh_size != sizeof(struct module)) {

		pr_err("module %s: .gnu.linkonce.this_module section size must match the kernel's built struct module size at run time\n",

		       info->name ?: "(missing .modinfo section or name field)");

		return -ENOEXEC;

	}



	info->index.mod = mod_idx;



	return 0;

}





/*

 * Check userspace passed ELF module against our expectations, and cache

 * useful variables for further processing as we go.
@@ -1944,7 +2006,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags) 
	unsigned int i;

	Elf_Shdr *shdr;

	int err;

	unsigned int num_mod_secs = 0, mod_idx;

	unsigned int num_sym_secs = 0, sym_idx;



	err = elf_validity_cache_sechdrs(info);
@@ -1954,16 +2015,15 @@ static int elf_validity_cache_copy(struct load_info *info, int flags) 
	if (err < 0)

		return err;

	err = elf_validity_cache_index_info(info);

	if (err < 0)

		return err;

	err = elf_validity_cache_index_mod(info);

	if (err < 0)

		return err;



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

		shdr = &info->sechdrs[i];

		switch (shdr->sh_type) {

		case SHT_NULL:

		case SHT_NOBITS:

			continue;

		case SHT_SYMTAB:

		if (shdr->sh_type == SHT_SYMTAB) {

			if (shdr->sh_link == SHN_UNDEF

			    || shdr->sh_link >= info->hdr->e_shnum) {

				pr_err("Invalid ELF sh_link!=SHN_UNDEF(%d) or (sh_link(%d) >= hdr->e_shnum(%d)\n",
@@ -1973,14 +2033,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags) 
			}

			num_sym_secs++;

			sym_idx = i;

			fallthrough;

		default:

			if (strcmp(info->secstrings + shdr->sh_name,

				   ".gnu.linkonce.this_module") == 0) {

				num_mod_secs++;

				mod_idx = i;

			}

			break;

		}

	}
@@ -1996,55 +2048,8 @@ static int elf_validity_cache_copy(struct load_info *info, int flags) 
	info->index.str = shdr->sh_link;

	info->strtab = (char *)info->hdr + info->sechdrs[info->index.str].sh_offset;



	/*

	 * The ".gnu.linkonce.this_module" ELF section is special. It is

	 * what modpost uses to refer to __this_module and let's use rely

	 * on THIS_MODULE to point to &__this_module properly. The kernel's

	 * modpost declares it on each modules's *.mod.c file. If the struct

	 * module of the kernel changes a full kernel rebuild is required.

	 *

	 * We have a few expectaions for this special section, the following

	 * code validates all this for us:

	 *

	 *   o Only one section must exist

	 *   o We expect the kernel to always have to allocate it: SHF_ALLOC

	 *   o The section size must match the kernel's run time's struct module

	 *     size

	 */

	if (num_mod_secs != 1) {

		pr_err("module %s: Only one .gnu.linkonce.this_module section must exist.\n",

		       info->name ?: "(missing .modinfo section or name field)");

		goto no_exec;

	}



	shdr = &info->sechdrs[mod_idx];



	/*

	 * This is already implied on the switch above, however let's be

	 * pedantic about it.

	 */

	if (shdr->sh_type == SHT_NOBITS) {

		pr_err("module %s: .gnu.linkonce.this_module section must have a size set\n",

		       info->name ?: "(missing .modinfo section or name field)");

		goto no_exec;

	}



	if (!(shdr->sh_flags & SHF_ALLOC)) {

		pr_err("module %s: .gnu.linkonce.this_module must occupy memory during process execution\n",

		       info->name ?: "(missing .modinfo section or name field)");

		goto no_exec;

	}



	if (shdr->sh_size != sizeof(struct module)) {

		pr_err("module %s: .gnu.linkonce.this_module section size must match the kernel's built struct module size at run time\n",

		       info->name ?: "(missing .modinfo section or name field)");

		goto no_exec;

	}



	info->index.mod = mod_idx;



	/* This is temporary: point mod into copy of data. */

	info->mod = (void *)info->hdr + shdr->sh_offset;

	info->mod = (void *)info->hdr + info->sechdrs[info->index.mod].sh_offset;



	/*

	 * If we didn't load the .modinfo 'name' field earlier, fall back to