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Commit 4a496226 authored by Jan Beulich's avatar Jan Beulich Committed by Rusty Russell
Browse files

module: reduce symbol table for loaded modules (v2) 



Discard all symbols not interesting for kallsyms use: absolute,
section, and in the common case (!KALLSYMS_ALL) data ones.

Signed-off-by: default avatarJan Beulich <jbeulich@novell.com>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 94a8d5ca

include/linux/module.h

+7 −3
Original line number Diff line number Diff line
@@ -308,9 +308,13 @@ struct module 
#endif



#ifdef CONFIG_KALLSYMS

	/* We keep the symbol and string tables for kallsyms. */

	Elf_Sym *symtab;

	unsigned int num_symtab;

	/*

	 * We keep the symbol and string tables for kallsyms.

	 * The core_* fields below are temporary, loader-only (they

	 * could really be discarded after module init).

	 */

	Elf_Sym *symtab, *core_symtab;

	unsigned int num_symtab, core_num_syms;

	char *strtab;



	/* Section attributes */

kernel/module.c

+87 −4
Original line number Diff line number Diff line
@@ -1862,13 +1862,68 @@ static char elf_type(const Elf_Sym *sym, 
	return '?';

}



static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs,

                           unsigned int shnum)

{

	const Elf_Shdr *sec;



	if (src->st_shndx == SHN_UNDEF

	    || src->st_shndx >= shnum

	    || !src->st_name)

		return false;



	sec = sechdrs + src->st_shndx;

	if (!(sec->sh_flags & SHF_ALLOC)

#ifndef CONFIG_KALLSYMS_ALL

	    || !(sec->sh_flags & SHF_EXECINSTR)

#endif

	    || (sec->sh_entsize & INIT_OFFSET_MASK))

		return false;



	return true;

}



static unsigned long layout_symtab(struct module *mod,

				   Elf_Shdr *sechdrs,

				   unsigned int symindex,

				   const Elf_Ehdr *hdr,

				   const char *secstrings)

{

	unsigned long symoffs;

	Elf_Shdr *symsect = sechdrs + symindex;

	const Elf_Sym *src;

	unsigned int i, nsrc, ndst;



	/* Put symbol section at end of init part of module. */

	symsect->sh_flags |= SHF_ALLOC;

	symsect->sh_entsize = get_offset(mod, &mod->init_size, symsect,

					 symindex) | INIT_OFFSET_MASK;

	DEBUGP("\t%s\n", secstrings + symsect->sh_name);



	src = (void *)hdr + symsect->sh_offset;

	nsrc = symsect->sh_size / sizeof(*src);

	for (ndst = i = 1; i < nsrc; ++i, ++src)

		if (is_core_symbol(src, sechdrs, hdr->e_shnum))

			++ndst;



	/* Append room for core symbols at end of core part. */

	symoffs = ALIGN(mod->core_size, symsect->sh_addralign ?: 1);

	mod->core_size = symoffs + ndst * sizeof(Elf_Sym);



	return symoffs;

}



static void add_kallsyms(struct module *mod,

			 Elf_Shdr *sechdrs,

			 unsigned int shnum,

			 unsigned int symindex,

			 unsigned int strindex,

			 unsigned long symoffs,

			 const char *secstrings)

{

	unsigned int i;

	unsigned int i, ndst;

	const Elf_Sym *src;

	Elf_Sym *dst;



	mod->symtab = (void *)sechdrs[symindex].sh_addr;

	mod->num_symtab = sechdrs[symindex].sh_size / sizeof(Elf_Sym);
@@ -1878,12 +1933,32 @@ static void add_kallsyms(struct module *mod, 
	for (i = 0; i < mod->num_symtab; i++)

		mod->symtab[i].st_info

			= elf_type(&mod->symtab[i], sechdrs, secstrings, mod);



	mod->core_symtab = dst = mod->module_core + symoffs;

	src = mod->symtab;

	*dst = *src;

	for (ndst = i = 1; i < mod->num_symtab; ++i, ++src) {

		if (!is_core_symbol(src, sechdrs, shnum))

			continue;

		dst[ndst] = *src;

		++ndst;

	}

	mod->core_num_syms = ndst;

}

#else

static inline unsigned long layout_symtab(struct module *mod,

					  Elf_Shdr *sechdrs,

					  unsigned int symindex,

					  const Elf_Hdr *hdr,

					  const char *secstrings)

{

}

static inline void add_kallsyms(struct module *mod,

				Elf_Shdr *sechdrs,

				unsigned int shnum,

				unsigned int symindex,

				unsigned int strindex,

				unsigned long symoffs,

				const char *secstrings)

{

}
@@ -1959,6 +2034,9 @@ static noinline struct module *load_module(void __user *umod, 
	struct module *mod;

	long err = 0;

	void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */

#ifdef CONFIG_KALLSYMS

	unsigned long symoffs;

#endif

	mm_segment_t old_fs;



	DEBUGP("load_module: umod=%p, len=%lu, uargs=%p\n",
@@ -2041,8 +2119,7 @@ static noinline struct module *load_module(void __user *umod, 
	sechdrs[infoindex].sh_flags &= ~(unsigned long)SHF_ALLOC;

	sechdrs[versindex].sh_flags &= ~(unsigned long)SHF_ALLOC;

#ifdef CONFIG_KALLSYMS

	/* Keep symbol and string tables for decoding later. */

	sechdrs[symindex].sh_flags |= SHF_ALLOC;

	/* Keep string table for decoding later. */

	sechdrs[strindex].sh_flags |= SHF_ALLOC;

#endif
@@ -2109,6 +2186,7 @@ static noinline struct module *load_module(void __user *umod, 
	   this is done generically; there doesn't appear to be any

	   special cases for the architectures. */

	layout_sections(mod, hdr, sechdrs, secstrings);

	symoffs = layout_symtab(mod, sechdrs, symindex, hdr, secstrings);



	/* Do the allocs. */

	ptr = module_alloc_update_bounds(mod->core_size);
@@ -2313,7 +2391,8 @@ static noinline struct module *load_module(void __user *umod, 
	percpu_modcopy(mod->percpu, (void *)sechdrs[pcpuindex].sh_addr,

		       sechdrs[pcpuindex].sh_size);



	add_kallsyms(mod, sechdrs, symindex, strindex, secstrings);

	add_kallsyms(mod, sechdrs, hdr->e_shnum, symindex, strindex,

		     symoffs, secstrings);



	if (!mod->taints) {

		struct _ddebug *debug;
@@ -2491,6 +2570,10 @@ SYSCALL_DEFINE3(init_module, void __user *, umod, 
	/* Drop initial reference. */

	module_put(mod);

	trim_init_extable(mod);

#ifdef CONFIG_KALLSYMS

	mod->num_symtab = mod->core_num_syms;

	mod->symtab = mod->core_symtab;

#endif

	module_free(mod, mod->module_init);

	mod->module_init = NULL;

	mod->init_size = 0;