LXR linux/arch/x86/kernel/livepatch.c

   1/*
   2 * livepatch.c - x86-specific Kernel Live Patching Core
   3 *
   4 * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
   5 * Copyright (C) 2014 SUSE
   6 *
   7 * This program is free software; you can redistribute it and/or
   8 * modify it under the terms of the GNU General Public License
   9 * as published by the Free Software Foundation; either version 2
  10 * of the License, or (at your option) any later version.
  11 *
  12 * This program is distributed in the hope that it will be useful,
  13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 * GNU General Public License for more details.
  16 *
  17 * You should have received a copy of the GNU General Public License
  18 * along with this program; if not, see <http://www.gnu.org/licenses/>.
  19 */
  20
  21#include <linux/module.h>
  22#include <linux/uaccess.h>
  23#include <asm/cacheflush.h>
  24#include <asm/page_types.h>
  25#include <asm/elf.h>
  26#include <asm/livepatch.h>
  27
  28/**
  29 * klp_write_module_reloc() - write a relocation in a module
  30 * @mod:        module in which the section to be modified is found
  31 * @type:       ELF relocation type (see asm/elf.h)
  32 * @loc:        address that the relocation should be written to
  33 * @value:      relocation value (sym address + addend)
  34 *
  35 * This function writes a relocation to the specified location for
  36 * a particular module.
  37 */
  38int klp_write_module_reloc(struct module *mod, unsigned long type,
  39                           unsigned long loc, unsigned long value)
  40{
  41        int ret, numpages, size = 4;
  42        bool readonly;
  43        unsigned long val;
  44        unsigned long core = (unsigned long)mod->module_core;
  45        unsigned long core_ro_size = mod->core_ro_size;
  46        unsigned long core_size = mod->core_size;
  47
  48        switch (type) {
  49        case R_X86_64_NONE:
  50                return 0;
  51        case R_X86_64_64:
  52                val = value;
  53                size = 8;
  54                break;
  55        case R_X86_64_32:
  56                val = (u32)value;
  57                break;
  58        case R_X86_64_32S:
  59                val = (s32)value;
  60                break;
  61        case R_X86_64_PC32:
  62                val = (u32)(value - loc);
  63                break;
  64        default:
  65                /* unsupported relocation type */
  66                return -EINVAL;
  67        }
  68
  69        if (loc < core || loc >= core + core_size)
  70                /* loc does not point to any symbol inside the module */
  71                return -EINVAL;
  72
  73        if (loc < core + core_ro_size)
  74                readonly = true;
  75        else
  76                readonly = false;
  77
  78        /* determine if the relocation spans a page boundary */
  79        numpages = ((loc & PAGE_MASK) == ((loc + size) & PAGE_MASK)) ? 1 : 2;
  80
  81        if (readonly)
  82                set_memory_rw(loc & PAGE_MASK, numpages);
  83
  84        ret = probe_kernel_write((void *)loc, &val, size);
  85
  86        if (readonly)
  87                set_memory_ro(loc & PAGE_MASK, numpages);
  88
  89        return ret;
  90}
  91