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/*
* libpulp - User-space Livepatching Library
*
* Copyright (C) 2021 SUSE Software Solutions GmbH
*
* This file is part of libpulp.
*
* libpulp is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* libpulp 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with libpulp. If not, see <http://www.gnu.org/licenses/>.
*/
#include <assert.h>
#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <argp.h>
#include <libelf.h>
#include "arguments.h"
#include "config.h"
#include "post.h"
#include "ulp_common.h"
Elf *elf;
/** Arch specific. */
void merge_nops_at_addr(Elf64_Addr addr, size_t amount);
/*
* Finds and returns the section identified by NAME. Returns NULL if no
* such section is found. Exits in error if the string table containing
* sections names is not found.
*/
Elf_Scn *
find_section_by_name(Elf *elf, const char *name)
{
char *str;
size_t string_table;
Elf_Scn *result;
Elf_Scn *section;
Elf64_Shdr *shdr;
if (elf_getshdrstrndx(elf, &string_table) == -1)
errx(1, "Unable to find the string table.\n");
/* Iterate over all sections */
result = NULL;
section = NULL;
while ((section = elf_nextscn(elf, section)) != NULL) {
shdr = elf64_getshdr(section);
str = elf_strptr(elf, string_table, shdr->sh_name);
if (strcmp(name, str) == 0) {
result = section;
break;
}
}
return result;
}
/*
* Iterates over all entries in the __patchable_function_entries
* section, finds the entry points of the functions they refer to, then
* replaces sequences of multiple nop instruction with multi-byte nops.
*/
static void
nops_fixup(void)
{
Elf_Scn *scn;
Elf_Data *data;
Elf64_Shdr *shdr;
Elf64_Addr addr;
scn = find_section_by_name(elf, "__patchable_function_entries");
if (scn == NULL)
return;
data = elf_getdata(scn, NULL);
shdr = elf64_getshdr(scn);
assert(data);
assert(shdr);
/* Iterate over the entries in __patchable_function_entries. */
for (Elf64_Xword i = 0; i < shdr->sh_size; i += sizeof(Elf64_Addr)) {
addr = *(Elf64_Addr *)(data->d_buf + i);
/*
* Each entry in the __patchable_function_entries section points to
* the start of the nop padding added at the prologue of functions
* compiled with -fpatchable-function-entries. However, only the
* nops that lay after the function entry point should be merged, so
* skip the preceding nops.
*/
addr += PRE_NOPS_LEN;
merge_nops_at_addr(addr, (ULP_NOPS_LEN - PRE_NOPS_LEN));
}
}
int
run_post(struct arguments *arguments)
{
int fd;
Elf_Scn *scn;
fd = open(arguments->args[0], O_RDWR);
if (fd == -1)
errx(EXIT_FAILURE, "Unable to open file '%s'.\n", arguments->args[0]);
elf_version(EV_CURRENT);
elf = elf_begin(fd, ELF_C_RDWR, NULL);
/* Do not let libelf change the layout of the elf file. */
assert(elf_flagelf(elf, ELF_C_SET, ELF_F_LAYOUT));
/* Sanity check. */
scn = find_section_by_name(elf, "__patchable_function_entries");
if (scn == NULL)
errx(EXIT_FAILURE,
"Section __patchable_function_entries not found.\n"
"(Binary not built with -fpatchable-function-entry?)\n");
nops_fixup();
/* Actually update the binary. */
if (elf_update(elf, ELF_C_WRITE) == -1)
errx(EXIT_FAILURE, "Error writing back to the Elf file.\n"
"(Elf file probably corrupted).\n");
elf_end(elf);
close(fd);
return 0;
}
struct argp_option *
get_command_option_post(void)
{
static struct argp_option options[] = {
{ 0, 0, 0, 0, "Options:", 0 },
{ "verbose", 'v', 0, 0, "Produce verbose output", 0 },
{ "quiet", 'q', 0, 0, "Don't produce any output", 0 },
{ 0 }
};
return options;
}
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