lib/buildid.c

   1 // SPDX-License-Identifier: GPL-2.0
   2
   3 #include <linux/buildid.h>
   4 #include <linux/cache.h>
   5 #include <linux/elf.h>
   6 #include <linux/kernel.h>
   7 #include <linux/pagemap.h>
   8
   9 #define BUILD_ID 3
  10
  11 /*
  12  * Parse build id from the note segment. This logic can be shared between
  13  * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
  14  * identical.
  15  */
  16 static int parse_build_id_buf(unsigned char *build_id,
  17                               __u32 *size,
  18                               const void *note_start,
  19                               Elf32_Word note_size)
  20 {
  21         Elf32_Word note_offs = 0, new_offs;
  22
  23         while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
  24                 Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
  25
  26                 if (nhdr->n_type == BUILD_ID &&
  27                     nhdr->n_namesz == sizeof("GNU") &&
  28                     !strcmp((char *)(nhdr + 1), "GNU") &&
  29                     nhdr->n_descsz > 0 &&
  30                     nhdr->n_descsz <= BUILD_ID_SIZE_MAX) {
  31                         memcpy(build_id,
  32                                note_start + note_offs +
  33                                ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
  34                                nhdr->n_descsz);
  35                         memset(build_id + nhdr->n_descsz, 0,
  36                                BUILD_ID_SIZE_MAX - nhdr->n_descsz);
  37                         if (size)
  38                                 *size = nhdr->n_descsz;
  39                         return 0;
  40                 }
  41                 new_offs = note_offs + sizeof(Elf32_Nhdr) +
  42                         ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4);
  43                 if (new_offs <= note_offs)  /* overflow */
  44                         break;
  45                 note_offs = new_offs;
  46         }
  47
  48         return -EINVAL;
  49 }
  50
  51 static inline int parse_build_id(const void *page_addr,
  52                                  unsigned char *build_id,
  53                                  __u32 *size,
  54                                  const void *note_start,
  55                                  Elf32_Word note_size)
  56 {
  57         /* check for overflow */
  58         if (note_start < page_addr || note_start + note_size < note_start)
  59                 return -EINVAL;
  60
  61         /* only supports note that fits in the first page */
  62         if (note_start + note_size > page_addr + PAGE_SIZE)
  63                 return -EINVAL;
  64
  65         return parse_build_id_buf(build_id, size, note_start, note_size);
  66 }
  67
  68 /* Parse build ID from 32-bit ELF */
  69 static int get_build_id_32(const void *page_addr, unsigned char *build_id,
  70                            __u32 *size)
  71 {
  72         Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr;
  73         Elf32_Phdr *phdr;
  74         int i;
  75
  76         /*
  77          * FIXME
  78          * Neither ELF spec nor ELF loader require that program headers
  79          * start immediately after ELF header.
  80          */
  81         if (ehdr->e_phoff != sizeof(Elf32_Ehdr))
  82                 return -EINVAL;
  83         /* only supports phdr that fits in one page */
  84         if (ehdr->e_phnum >
  85             (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
  86                 return -EINVAL;
  87
  88         phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr));
  89
  90         for (i = 0; i < ehdr->e_phnum; ++i) {
  91                 if (phdr[i].p_type == PT_NOTE &&
  92                     !parse_build_id(page_addr, build_id, size,
  93                                     page_addr + phdr[i].p_offset,
  94                                     phdr[i].p_filesz))
  95                         return 0;
  96         }
  97         return -EINVAL;
  98 }
  99
 100 /* Parse build ID from 64-bit ELF */
 101 static int get_build_id_64(const void *page_addr, unsigned char *build_id,
 102                            __u32 *size)
 103 {
 104         Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr;
 105         Elf64_Phdr *phdr;
 106         int i;
 107
 108         /*
 109          * FIXME
 110          * Neither ELF spec nor ELF loader require that program headers
 111          * start immediately after ELF header.
 112          */
 113         if (ehdr->e_phoff != sizeof(Elf64_Ehdr))
 114                 return -EINVAL;
 115         /* only supports phdr that fits in one page */
 116         if (ehdr->e_phnum >
 117             (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))
 118                 return -EINVAL;
 119
 120         phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr));
 121
 122         for (i = 0; i < ehdr->e_phnum; ++i) {
 123                 if (phdr[i].p_type == PT_NOTE &&
 124                     !parse_build_id(page_addr, build_id, size,
 125                                     page_addr + phdr[i].p_offset,
 126                                     phdr[i].p_filesz))
 127                         return 0;
 128         }
 129         return -EINVAL;
 130 }
 131
 132 /*
 133  * Parse build ID of ELF file mapped to vma
 134  * @vma:      vma object
 135  * @build_id: buffer to store build id, at least BUILD_ID_SIZE long
 136  * @size:     returns actual build id size in case of success
 137  *
 138  * Return: 0 on success, -EINVAL otherwise
 139  */
 140 int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
 141                    __u32 *size)
 142 {
 143         Elf32_Ehdr *ehdr;
 144         struct page *page;
 145         void *page_addr;
 146         int ret;
 147
 148         /* only works for page backed storage  */
 149         if (!vma->vm_file)
 150                 return -EINVAL;
 151
 152         page = find_get_page(vma->vm_file->f_mapping, 0);
 153         if (!page)
 154                 return -EFAULT; /* page not mapped */
 155
 156         ret = -EINVAL;
 157         page_addr = kmap_local_page(page);
 158         ehdr = (Elf32_Ehdr *)page_addr;
 159
 160         /* compare magic x7f "ELF" */
 161         if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)
 162                 goto out;
 163
 164         /* only support executable file and shared object file */
 165         if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)
 166                 goto out;
 167
 168         if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
 169                 ret = get_build_id_32(page_addr, build_id, size);
 170         else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
 171                 ret = get_build_id_64(page_addr, build_id, size);
 172 out:
 173         kunmap_local(page_addr);
 174         put_page(page);
 175         return ret;
 176 }
 177
 178 /**
 179  * build_id_parse_buf - Get build ID from a buffer
 180  * @buf:      ELF note section(s) to parse
 181  * @buf_size: Size of @buf in bytes
 182  * @build_id: Build ID parsed from @buf, at least BUILD_ID_SIZE_MAX long
 183  *
 184  * Return: 0 on success, -EINVAL otherwise
 185  */
 186 int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size)
 187 {
 188         return parse_build_id_buf(build_id, NULL, buf, buf_size);
 189 }
 190
 191 #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) || IS_ENABLED(CONFIG_VMCORE_INFO)
 192 unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX] __ro_after_init;
 193
 194 /**
 195  * init_vmlinux_build_id - Compute and stash the running kernel's build ID
 196  */
 197 void __init init_vmlinux_build_id(void)
 198 {
 199         extern const void __start_notes;
 200         extern const void __stop_notes;
 201         unsigned int size = &__stop_notes - &__start_notes;
 202
 203         build_id_parse_buf(&__start_notes, vmlinux_build_id, size);
 204 }
 205 #endif