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  */
  38 int 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 }