Commit 1c7651f4 authored by Eugene Loh's avatar Eugene Loh Committed by Jessica Yu
Browse files

kallsyms: store type information in its own array 



When a module is loaded, its symbols' Elf_Sym information is stored
in a symtab.  Further, type information is also captured.  Since
Elf_Sym has no type field, historically the st_info field has been
hijacked for storing type:  st_info was overwritten.

commit 5439c985 ("module: Overwrite
st_size instead of st_info") changes that practice, as its one-liner
indicates.  Unfortunately, this change overwrites symbol size,
information that a tool like DTrace expects to find.

Allocate a typetab array to store type information so that no Elf_Sym
field needs to be overwritten.

Fixes: 5439c985 ("module: Overwrite st_size instead of st_info")
Signed-off-by: default avatarEugene Loh <eugene.loh@oracle.com>
Reviewed-by: default avatarNick Alcock <nick.alcock@oracle.com>
[jeyu: renamed typeoff -> typeoffs ]
Signed-off-by: default avatarJessica Yu <jeyu@kernel.org>
parent 9672e2cb

include/linux/module.h

+1 −0
Original line number Diff line number Diff line
@@ -331,6 +331,7 @@ struct mod_kallsyms { 
	Elf_Sym *symtab;

	unsigned int num_symtab;

	char *strtab;

	char *typetab;

};



#ifdef CONFIG_LIVEPATCH

kernel/module-internal.h

+1 −1
Original line number Diff line number Diff line
@@ -20,7 +20,7 @@ struct load_info { 
	unsigned long len;

	Elf_Shdr *sechdrs;

	char *secstrings, *strtab;

	unsigned long symoffs, stroffs;

	unsigned long symoffs, stroffs, init_typeoffs, core_typeoffs;

	struct _ddebug *debug;

	unsigned int num_debug;

	bool sig_ok;

kernel/module.c

+14 −7
Original line number Diff line number Diff line
@@ -2647,6 +2647,8 @@ static void layout_symtab(struct module *mod, struct load_info *info) 
	info->symoffs = ALIGN(mod->core_layout.size, symsect->sh_addralign ?: 1);

	info->stroffs = mod->core_layout.size = info->symoffs + ndst * sizeof(Elf_Sym);

	mod->core_layout.size += strtab_size;

	info->core_typeoffs = mod->core_layout.size;

	mod->core_layout.size += ndst * sizeof(char);

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



	/* Put string table section at end of init part of module. */
@@ -2660,6 +2662,8 @@ static void layout_symtab(struct module *mod, struct load_info *info) 
				      __alignof__(struct mod_kallsyms));

	info->mod_kallsyms_init_off = mod->init_layout.size;

	mod->init_layout.size += sizeof(struct mod_kallsyms);

	info->init_typeoffs = mod->init_layout.size;

	mod->init_layout.size += nsrc * sizeof(char);

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

}
@@ -2683,20 +2687,23 @@ static void add_kallsyms(struct module *mod, const struct load_info *info) 
	mod->kallsyms->num_symtab = symsec->sh_size / sizeof(Elf_Sym);

	/* Make sure we get permanent strtab: don't use info->strtab. */

	mod->kallsyms->strtab = (void *)info->sechdrs[info->index.str].sh_addr;

	mod->kallsyms->typetab = mod->init_layout.base + info->init_typeoffs;



	/* Set types up while we still have access to sections. */

	for (i = 0; i < mod->kallsyms->num_symtab; i++)

		mod->kallsyms->symtab[i].st_size

			= elf_type(&mod->kallsyms->symtab[i], info);



	/* Now populate the cut down core kallsyms for after init. */

	/*

	 * Now populate the cut down core kallsyms for after init

	 * and set types up while we still have access to sections.

	 */

	mod->core_kallsyms.symtab = dst = mod->core_layout.base + info->symoffs;

	mod->core_kallsyms.strtab = s = mod->core_layout.base + info->stroffs;

	mod->core_kallsyms.typetab = mod->core_layout.base + info->core_typeoffs;

	src = mod->kallsyms->symtab;

	for (ndst = i = 0; i < mod->kallsyms->num_symtab; i++) {

		mod->kallsyms->typetab[i] = elf_type(src + i, info);

		if (i == 0 || is_livepatch_module(mod) ||

		    is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum,

				   info->index.pcpu)) {

			mod->core_kallsyms.typetab[ndst] =

			    mod->kallsyms->typetab[i];

			dst[ndst] = src[i];

			dst[ndst++].st_name = s - mod->core_kallsyms.strtab;

			s += strlcpy(s, &mod->kallsyms->strtab[src[i].st_name],
@@ -4080,7 +4087,7 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type, 
			const Elf_Sym *sym = &kallsyms->symtab[symnum];



			*value = kallsyms_symbol_value(sym);

			*type = sym->st_size;

			*type = kallsyms->typetab[symnum];

			strlcpy(name, kallsyms_symbol_name(kallsyms, symnum), KSYM_NAME_LEN);

			strlcpy(module_name, mod->name, MODULE_NAME_LEN);

			*exported = is_exported(name, *value, mod);

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