the-tree/lib/buildid.c

0001 // SPDX-License-Identifier: GPL-2.0
0002
0003 #include <linux/buildid.h>
0004 #include <linux/cache.h>
0005 #include <linux/elf.h>
0006 #include <linux/kernel.h>
0007 #include <linux/pagemap.h>
0008
0009 #define BUILD_ID 3
0010
0011 /*
0012  * Parse build id from the note segment. This logic can be shared between
0013  * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
0014  * identical.
0015  */
0016 static int parse_build_id_buf(unsigned char *build_id,
0017                   __u32 *size,
0018                   const void *note_start,
0019                   Elf32_Word note_size)
0020 {
0021     Elf32_Word note_offs = 0, new_offs;
0022
0023     while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
0024         Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
0025
0026         if (nhdr->n_type == BUILD_ID &&
0027             nhdr->n_namesz == sizeof("GNU") &&
0028             !strcmp((char *)(nhdr + 1), "GNU") &&
0029             nhdr->n_descsz > 0 &&
0030             nhdr->n_descsz <= BUILD_ID_SIZE_MAX) {
0031             memcpy(build_id,
0032                    note_start + note_offs +
0033                    ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
0034                    nhdr->n_descsz);
0035             memset(build_id + nhdr->n_descsz, 0,
0036                    BUILD_ID_SIZE_MAX - nhdr->n_descsz);
0037             if (size)
0038                 *size = nhdr->n_descsz;
0039             return 0;
0040         }
0041         new_offs = note_offs + sizeof(Elf32_Nhdr) +
0042             ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4);
0043         if (new_offs <= note_offs)  /* overflow */
0044             break;
0045         note_offs = new_offs;
0046     }
0047
0048     return -EINVAL;
0049 }
0050
0051 static inline int parse_build_id(const void *page_addr,
0052                  unsigned char *build_id,
0053                  __u32 *size,
0054                  const void *note_start,
0055                  Elf32_Word note_size)
0056 {
0057     /* check for overflow */
0058     if (note_start < page_addr || note_start + note_size < note_start)
0059         return -EINVAL;
0060
0061     /* only supports note that fits in the first page */
0062     if (note_start + note_size > page_addr + PAGE_SIZE)
0063         return -EINVAL;
0064
0065     return parse_build_id_buf(build_id, size, note_start, note_size);
0066 }
0067
0068 /* Parse build ID from 32-bit ELF */
0069 static int get_build_id_32(const void *page_addr, unsigned char *build_id,
0070                __u32 *size)
0071 {
0072     Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr;
0073     Elf32_Phdr *phdr;
0074     int i;
0075
0076     /* only supports phdr that fits in one page */
0077     if (ehdr->e_phnum >
0078         (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
0079         return -EINVAL;
0080
0081     phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr));
0082
0083     for (i = 0; i < ehdr->e_phnum; ++i) {
0084         if (phdr[i].p_type == PT_NOTE &&
0085             !parse_build_id(page_addr, build_id, size,
0086                     page_addr + phdr[i].p_offset,
0087                     phdr[i].p_filesz))
0088             return 0;
0089     }
0090     return -EINVAL;
0091 }
0092
0093 /* Parse build ID from 64-bit ELF */
0094 static int get_build_id_64(const void *page_addr, unsigned char *build_id,
0095                __u32 *size)
0096 {
0097     Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr;
0098     Elf64_Phdr *phdr;
0099     int i;
0100
0101     /* only supports phdr that fits in one page */
0102     if (ehdr->e_phnum >
0103         (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))
0104         return -EINVAL;
0105
0106     phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr));
0107
0108     for (i = 0; i < ehdr->e_phnum; ++i) {
0109         if (phdr[i].p_type == PT_NOTE &&
0110             !parse_build_id(page_addr, build_id, size,
0111                     page_addr + phdr[i].p_offset,
0112                     phdr[i].p_filesz))
0113             return 0;
0114     }
0115     return -EINVAL;
0116 }
0117
0118 /*
0119  * Parse build ID of ELF file mapped to vma
0120  * @vma:      vma object
0121  * @build_id: buffer to store build id, at least BUILD_ID_SIZE long
0122  * @size:     returns actual build id size in case of success
0123  *
0124  * Return: 0 on success, -EINVAL otherwise
0125  */
0126 int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
0127            __u32 *size)
0128 {
0129     Elf32_Ehdr *ehdr;
0130     struct page *page;
0131     void *page_addr;
0132     int ret;
0133
0134     /* only works for page backed storage  */
0135     if (!vma->vm_file)
0136         return -EINVAL;
0137
0138     page = find_get_page(vma->vm_file->f_mapping, 0);
0139     if (!page)
0140         return -EFAULT; /* page not mapped */
0141
0142     ret = -EINVAL;
0143     page_addr = kmap_atomic(page);
0144     ehdr = (Elf32_Ehdr *)page_addr;
0145
0146     /* compare magic x7f "ELF" */
0147     if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)
0148         goto out;
0149
0150     /* only support executable file and shared object file */
0151     if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)
0152         goto out;
0153
0154     if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
0155         ret = get_build_id_32(page_addr, build_id, size);
0156     else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
0157         ret = get_build_id_64(page_addr, build_id, size);
0158 out:
0159     kunmap_atomic(page_addr);
0160     put_page(page);
0161     return ret;
0162 }
0163
0164 /**
0165  * build_id_parse_buf - Get build ID from a buffer
0166  * @buf:      Elf note section(s) to parse
0167  * @buf_size: Size of @buf in bytes
0168  * @build_id: Build ID parsed from @buf, at least BUILD_ID_SIZE_MAX long
0169  *
0170  * Return: 0 on success, -EINVAL otherwise
0171  */
0172 int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size)
0173 {
0174     return parse_build_id_buf(build_id, NULL, buf, buf_size);
0175 }
0176
0177 #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) || IS_ENABLED(CONFIG_CRASH_CORE)
0178 unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX] __ro_after_init;
0179
0180 /**
0181  * init_vmlinux_build_id - Compute and stash the running kernel's build ID
0182  */
0183 void __init init_vmlinux_build_id(void)
0184 {
0185     extern const void __start_notes __weak;
0186     extern const void __stop_notes __weak;
0187     unsigned int size = &__stop_notes - &__start_notes;
0188
0189     build_id_parse_buf(&__start_notes, vmlinux_build_id, size);
0190 }
0191 #endif