/*

	Copyright(C) 2016, Red Hat, Inc., Stanislav Kozina

	This program is free software: you can redistribute it and/or modify

	it under the terms of the GNU General Public License as published by

	the Free Software Foundation, either version 3 of the License, or

	(at your option) any later version.

	This program is distributed in the hope that it will be useful,

	but WITHOUT ANY WARRANTY; without even the implied warranty of

	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License

	along with this program.  If not, see <http://www.gnu.org/licenses/>.

*/

/*

 * This file contains the code which reads the __ksymtab section of the kernel

 * binaries to ensure that the symbol we parse is actually exported using the

 * EXPORT_SYMBOL() macro.

 */

#include <stdlib.h>

#include <unistd.h>

#include <stdio.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <stdbool.h>

#include <fcntl.h>

#include <string.h>

#include <errno.h>

#include <assert.h>

#include <libelf.h>

#include <gelf.h>

#include "main.h"

#include "utils.h"

#include "hash.h"

#include "ksymtab.h"

#define	KSYMTAB_STRINGS	"__ksymtab_strings"

#define SYMTAB		".symtab"

#define STRTAB		".strtab"

#define KSYMTAB_SIZE 8192

struct ksymtab {

	struct hash *hash;

	size_t mark_count;

};

struct ksym;

static int elf_get_section(Elf *elf,

			   size_t shstrndx,

			   const char *section,

			   const char **d_data,

			   size_t *size)

{

	Elf_Scn *scn;

	GElf_Shdr shdr;

	char *name;

	Elf_Data *data;

	scn = elf_nextscn(elf, NULL);

	for (; scn != NULL; scn = elf_nextscn(elf, scn)) {

		if (gelf_getshdr(scn, &shdr) != &shdr)

			fail("getshdr() failed: %s\n", elf_errmsg(-1));

		name = elf_strptr(elf, shstrndx, shdr.sh_name);

		if (name == NULL)

			fail("elf_strptr() failed: %s\n", elf_errmsg(-1));

		if (strcmp(name, section) == 0)

			break;

	}

	if (scn == NULL) /* no suitable section */

		return -1;

	/*

	 * This is unlucky. Fedora/EL builds -debuginfo packages by running

	 * eu-strip --reloc-debug-sections which places only standard .debug*

	 * sections into the -debuginfo modules. The sections which cannot

	 * be stripped completely (because they are allocated) are changed

	 * to SHT_NOBITS type to indicate you need to look in the original

	 * (non-debug) module for them. But those are xzipped.

	 * So we reject such stuff. We only support fresh output from the

	 * kernel build.

	 */

	if (shdr.sh_type == SHT_NOBITS) {

		printf("The %s section has type SHT_NOBITS. Most likely you're "

		    "running this tool on modules coming from kernel-debuginfo "

		    "packages. They don't contain the %s section, you need to "

		    "use the raw modules before they are stripped\n", section,

		    section);

		exit(1);

	}

	if (gelf_getshdr(scn, &shdr) != &shdr)

		fail("getshdr() failed: %s\n", elf_errmsg(-1));

	data = elf_getdata(scn, NULL);

	if (data == NULL || data->d_size == 0)

		fail("%s section empty!\n", section);

	*d_data = data->d_buf;

	*size = data->d_size;

	return 0;

}

struct elf_data *elf_open(const char *filename)

{

	Elf *elf;

	int fd;

	int class;

	GElf_Ehdr *ehdr;

	size_t shstrndx;

	struct elf_data *data = NULL;

	if (elf_version(EV_CURRENT) == EV_NONE)

		fail("elf_version() failed: %s\n", elf_errmsg(-1));

	fd = open(filename, O_RDONLY, 0);

	if (fd < 0)

		fail("Failed to open file %s: %s\n", filename,

		     strerror(errno));

	elf = elf_begin(fd, ELF_C_READ, NULL);

	if (elf == NULL)

		fail("elf_begin() failed: %s\n", elf_errmsg(-1));

	if (elf_kind(elf) != ELF_K_ELF) {

		printf("Doesn't look like an ELF file, ignoring: %s\n",

		       filename);

		(void) elf_end(elf);

		(void) close(fd);

		goto out;

	}

	ehdr = safe_zmalloc(sizeof(*ehdr));

	if (gelf_getehdr(elf, ehdr) == NULL)

		fail("getehdr() failed: %s\n", elf_errmsg(-1));

	class = gelf_getclass(elf);

	if (class != ELFCLASS64) {

		printf("Unsupported elf class of %s: %d\n", filename, class);

		free(ehdr);

		(void) elf_end(elf);

		(void) close(fd);

		goto out;

	}

	/*

	 * Get section index of the string table associated with the section

	 * headers in the ELF file.

	 * Required by elf_get_section calls.

	 */

	if (elf_getshdrstrndx(elf, &shstrndx) != 0)

		fail("elf_getshdrstrndx() failed: %s\n", elf_errmsg(-1))

	data = safe_zmalloc(sizeof(*data));

	data->fd = fd;

	data->elf = elf;

	data->ehdr = ehdr;

	data->shstrndx = shstrndx;

out:

	return data;

}

void elf_close(struct elf_data *ed)

{

	if (ed == NULL)

		return;

	(void) elf_end(ed->elf);

	(void) close(ed->fd);

}

static void elf_for_each_global_sym(struct elf_data *ed,

				    void (*fn)(const char *name,

					       uint64_t value,

					       int binding,

					       void *ctx),

				    void *ctx)

{

	const Elf64_Sym *end;

	Elf64_Sym *sym;

	int binding;

	const char *name;

	const char *data;

	size_t size;

	if (elf_get_section(ed->elf, ed->shstrndx, SYMTAB, &data, &size) < 0)

		return;

	sym = (Elf64_Sym *)data;

	end = (Elf64_Sym *)(data + size);

	sym++; /* skip first zero record */

	for (; sym < end; sym++) {

		binding = ELF64_ST_BIND(sym->st_info);

		if (!(binding == STB_GLOBAL ||

		       binding == STB_WEAK))

			continue;

		if (sym->st_name == 0)

			continue;

		if (sym->st_name > ed->strtab_size)

			fail("Symbol name index %d out of range %ld\n",

			    sym->st_name, ed->strtab_size);

		name = ed->strtab + sym->st_name;

		if (name == NULL)

			fail("Could not find symbol name\n");

		fn(name, sym->st_value, binding, ctx);

	}

}

void ksymtab_ksym_mark(struct ksym *ksym)

{

	if (!ksym->mark)

		ksym->ksymtab->mark_count++;

	ksym->mark = true;

}

static void ksymtab_ksym_free(void *arg)

{

	struct ksym *ksym = arg;

	free(ksym->link);

	free(ksym);

}

void ksymtab_free(struct ksymtab *ksymtab)

{

	struct hash *h;

	if (ksymtab == NULL)

		return;

	h = ksymtab->hash;

	hash_free(h);

	free(ksymtab);

}

struct ksymtab *ksymtab_new(size_t size)

{

	struct hash *h;

	struct ksymtab *ksymtab;

	h = hash_new(size, ksymtab_ksym_free);

	assert(h != NULL);

	ksymtab = safe_zmalloc(sizeof(*ksymtab));

	ksymtab->hash = h;

	/* ksymtab->mark_count is zeroed by the allocator */

	return ksymtab;

}

struct ksym *ksymtab_add_sym(struct ksymtab *ksymtab,

			     const char *str,

			     size_t len,

			     uint64_t value)

{

	struct hash *h = ksymtab->hash;

	struct ksym *ksym;

	ksym = safe_zmalloc(sizeof(*ksym) + len + 1);

	memcpy(ksym->key, str, len);

	ksym->key[len] = '\0';

	ksym->value = value;

	ksym->ksymtab = ksymtab;

	/* ksym->link is zeroed by the allocator */

	hash_add(h, ksym->key, ksym);

	return ksym;

}

struct ksym *ksymtab_copy_sym(struct ksymtab *ksymtab, struct ksym *ksym)

{

	const char *name = ksymtab_ksym_get_name(ksym);

	uint64_t value = ksymtab_ksym_get_value(ksym);

	char *link = ksymtab_ksym_get_link(ksym);

	struct ksym *new;

	new = ksymtab_add_sym(ksymtab, name, strlen(name), value);

	ksymtab_ksym_set_link(new, link);

	return new;

}

struct ksym *ksymtab_find(struct ksymtab *ksymtab, const char *name)

{

	struct ksym *v;

	struct hash *h = ksymtab->hash;

	if (name == NULL)

		return NULL;

	v = hash_find(h, name);

	if (v == NULL)

		return NULL;

	return v;

}

size_t ksymtab_len(struct ksymtab *ksymtab)

{

	struct hash *h;

	if (ksymtab == NULL)

		return 0;

	h = ksymtab->hash;

	return hash_get_count(h);

}

size_t ksymtab_mark_count(struct ksymtab *ksymtab)

{

	return ksymtab->mark_count;

}

void ksymtab_for_each(struct ksymtab *ksymtab,

		      void (*f)(struct ksym *, void *),

		      void *ctx)

{

	struct hash *h;

	struct hash_iter iter;

	const void *v;

	struct ksym *vv;

	if (ksymtab == NULL)

		return;

	h = ksymtab->hash;

	hash_iter_init(h, &iter);

	while (hash_iter_next(&iter, NULL, &v)) {

		vv = (struct ksym *)v;

		f(vv, ctx);

	}

}

/* Parses raw content of  __ksymtab_strings section to a ksymtab */

static struct ksymtab *parse_ksymtab_strings(const char *d_buf, size_t d_size)

{

	char *p, *oldp;

	size_t size = 0;

	size_t i = 0;

	struct ksymtab *res;

	res = ksymtab_new(KSYMTAB_SIZE);

	p = oldp = (char *)d_buf;

	/* Make sure we have the final '\0' */

	if (p[d_size - 1] != '\0')

		fail("Mallformed " KSYMTAB_STRINGS " section: %s\n", p);

	for (size = 0; size < d_size; size++, p++) {

		/* End of symbol? */

		if (*p == '\0') {

			size_t len = p - oldp;

			/* Skip empty strings */

			if (len == 0) {

				oldp = p + 1;

				continue;

			}

			ksymtab_add_sym(res, oldp, len, i);

			i++;

			oldp = p + 1;

		}

	}

	return res;

}

/*

 * An entry for address -> symbol mapping.

 * The key will be "value".

 * We can use name pointer directly from the elf,

 * it will be freed later.

 */

struct map_entry {

	uint64_t value;

	const char *name;

};

static struct map_entry *map_entry_new(uint64_t value, const char *name)

{

	struct map_entry *res;

	res = safe_zmalloc(sizeof(*res));

	res->value = value;

	res->name = name;

	return res;

}

struct weak_filter_ctx {

	struct ksymtab *ksymtab;

	struct ksymtab *weaks;

	struct hash *map;

};

/*

 * Does two things in one pass on the symbol table:

 * 1) makes address -> symbol map for GLOBAL symbols;

 * 2) collecs subset of EXPORTed symbol, which have WEAK binding.

 */

static void weak_filter(const char *name, uint64_t value, int bind, void *_ctx)

{

	struct weak_filter_ctx *ctx = _ctx;

	struct map_entry *m;

	struct ksym *ksym;

	if (bind == STB_GLOBAL) {

		m = map_entry_new(value, name);

		hash_add_bin(ctx->map,

			     (const char *)&m->value, sizeof(m->value), m);

		return;

	}

	/* WEAK handling */

	ksym = ksymtab_find(ctx->ksymtab, name);

	if (ksym == NULL)

		/* skip non-exported aliases */

		return;

	ksymtab_add_sym(ctx->weaks, name, strlen(name), value);

}

struct weak_to_alias_ctx {

	struct ksymtab *aliases;

	struct hash *map;

};

static void weak_to_alias(struct ksym *ksym, void *_ctx)

{

	struct weak_to_alias_ctx *ctx = _ctx;

	struct map_entry *m;

	uint64_t value = ksymtab_ksym_get_value(ksym);

	const char *name = ksymtab_ksym_get_name(ksym);

	struct ksym *alias;

	m = hash_find_bin(ctx->map, (const char *)&value, sizeof(value));

	if (m == NULL)

		/* there is no GLOBAL alias for the WEAK exported symbol */

		return;

	alias = ksymtab_add_sym(ctx->aliases, m->name, strlen(m->name), 0);

	ksymtab_ksym_set_link(alias, name);

}

static struct ksymtab *ksymtab_weaks_to_aliases(struct ksymtab *weaks,

						struct hash *map)

{

	struct ksymtab *aliases;

	struct weak_to_alias_ctx ctx;

	aliases = ksymtab_new(KSYMTAB_SIZE);

	if (aliases == NULL)

		fail("Cannot create ksymtab\n");

	ctx.aliases = aliases;

	ctx.map = map;

	ksymtab_for_each(weaks, weak_to_alias, &ctx;;

	return aliases;

}

/*

 * Generate weak aliases for the symbols, found in the list of exported.

 * It will work correctly for one alias only.

 */

static struct ksymtab *ksymtab_find_aliases(struct ksymtab *ksymtab,

					    struct elf_data *elf)

{

	struct ksymtab *aliases;

	struct ksymtab *weaks;

	struct hash *map; /* address to name mapping */

	struct weak_filter_ctx ctx;

	weaks = ksymtab_new(KSYMTAB_SIZE);

	if (weaks == NULL)

		fail("Cannot create weaks symtab\n");

	map = hash_new(KSYMTAB_SIZE, free);

	if (map == NULL)

		fail("Cannot create address->symbol mapping hash\n");

	ctx.ksymtab = ksymtab;

	ctx.weaks = weaks;

	ctx.map = map;

	/*

	 * If there's a weak symbol on the whitelist,

	 * we need to find the proper global

	 * symbol to generate the type for it.

	 *

	 * It is done in two steps below:

	 * 1) create address -> global symbol mapping and

	 *    suitable weak symbol list;

	 * 2) for all weak symbols find its alias with the mapping.

	 */

	elf_for_each_global_sym(elf, weak_filter, &ctx;;

	aliases = ksymtab_weaks_to_aliases(weaks, map);

	hash_free(map);

	ksymtab_free(weaks);

	return aliases;

}

int elf_get_endianness(struct elf_data *data, unsigned int *endianness)

{

	if (data->ehdr->e_ident[EI_DATA] != ELFDATA2LSB &&

	     data->ehdr->e_ident[EI_DATA] != ELFDATA2MSB) {

		printf("Unsupported ELF endianness (EI_DATA) found: %d.\n",

		     data->ehdr->e_ident[EI_DATA]);

		return 1;

	}

	*endianness = data->ehdr->e_ident[EI_DATA];

	return 0;

}

static inline int elf_get_strtab(struct elf_data *data)

{

	const char *strtab;

	size_t strtab_size;

	if (elf_get_section(data->elf, data->shstrndx, STRTAB, &strtab,

			   &strtab_size) < 0) {

		return 1;

	}

	data->strtab = strtab;

	data->strtab_size = strtab_size;

	return 0;

}

/*

 * Build list of exported symbols, ie. read seciton __ksymtab_strings,

 * analyze symbol table and create table of aliases -- list of global symbols,

 * which have the same addresses, as weak symbols,

 * mentioned by __ksymtab_strings

 */

int elf_get_exported(struct elf_data *data, struct ksymtab **ksymtab,

		     struct ksymtab **aliases)

{

	const char *ksymtab_raw;

	size_t ksymtab_sz;

	if (elf_get_strtab(data) > 0)

		return 1;

	if (elf_get_section(data->elf, data->shstrndx, KSYMTAB_STRINGS,

			   &ksymtab_raw, &ksymtab_sz) < 0)

		return 1;

	*ksymtab = parse_ksymtab_strings(ksymtab_raw, ksymtab_sz);

	*aliases = ksymtab_find_aliases(*ksymtab, data);

	return 0;

}