LXR linux/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 */
  16static 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
  51static 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 */
  69static 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        /* only supports phdr that fits in one page */
  77        if (ehdr->e_phnum >
  78            (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
  79                return -EINVAL;
  80
  81        phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr));
  82
  83        for (i = 0; i < ehdr->e_phnum; ++i) {
  84                if (phdr[i].p_type == PT_NOTE &&
  85                    !parse_build_id(page_addr, build_id, size,
  86                                    page_addr + phdr[i].p_offset,
  87                                    phdr[i].p_filesz))
  88                        return 0;
  89        }
  90        return -EINVAL;
  91}
  92
  93/* Parse build ID from 64-bit ELF */
  94static int get_build_id_64(const void *page_addr, unsigned char *build_id,
  95                           __u32 *size)
  96{
  97        Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr;
  98        Elf64_Phdr *phdr;
  99        int i;
 100
 101        /* only supports phdr that fits in one page */
 102        if (ehdr->e_phnum >
 103            (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))
 104                return -EINVAL;
 105
 106        phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr));
 107
 108        for (i = 0; i < ehdr->e_phnum; ++i) {
 109                if (phdr[i].p_type == PT_NOTE &&
 110                    !parse_build_id(page_addr, build_id, size,
 111                                    page_addr + phdr[i].p_offset,
 112                                    phdr[i].p_filesz))
 113                        return 0;
 114        }
 115        return -EINVAL;
 116}
 117
 118/*
 119 * Parse build ID of ELF file mapped to vma
 120 * @vma:      vma object
 121 * @build_id: buffer to store build id, at least BUILD_ID_SIZE long
 122 * @size:     returns actual build id size in case of success
 123 *
 124 * Return: 0 on success, -EINVAL otherwise
 125 */
 126int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
 127                   __u32 *size)
 128{
 129        Elf32_Ehdr *ehdr;
 130        struct page *page;
 131        void *page_addr;
 132        int ret;
 133
 134        /* only works for page backed storage  */
 135        if (!vma->vm_file)
 136                return -EINVAL;
 137
 138        page = find_get_page(vma->vm_file->f_mapping, 0);
 139        if (!page)
 140                return -EFAULT; /* page not mapped */
 141
 142        ret = -EINVAL;
 143        page_addr = kmap_atomic(page);
 144        ehdr = (Elf32_Ehdr *)page_addr;
 145
 146        /* compare magic x7f "ELF" */
 147        if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)
 148                goto out;
 149
 150        /* only support executable file and shared object file */
 151        if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)
 152                goto out;
 153
 154        if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
 155                ret = get_build_id_32(page_addr, build_id, size);
 156        else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
 157                ret = get_build_id_64(page_addr, build_id, size);
 158out:
 159        kunmap_atomic(page_addr);
 160        put_page(page);
 161        return ret;
 162}
 163
 164/**
 165 * build_id_parse_buf - Get build ID from a buffer
 166 * @buf:      Elf note section(s) to parse
 167 * @buf_size: Size of @buf in bytes
 168 * @build_id: Build ID parsed from @buf, at least BUILD_ID_SIZE_MAX long
 169 *
 170 * Return: 0 on success, -EINVAL otherwise
 171 */
 172int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size)
 173{
 174        return parse_build_id_buf(build_id, NULL, buf, buf_size);
 175}
 176
 177#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) || IS_ENABLED(CONFIG_CRASH_CORE)
 178unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX] __ro_after_init;
 179
 180/**
 181 * init_vmlinux_build_id - Compute and stash the running kernel's build ID
 182 */
 183void __init init_vmlinux_build_id(void)
 184{
 185        extern const void __start_notes __weak;
 186        extern const void __stop_notes __weak;
 187        unsigned int size = &__stop_notes - &__start_notes;
 188
 189        build_id_parse_buf(&__start_notes, vmlinux_build_id, size);
 190}
 191#endif
 192