1 // SPDX-License-Identifier: GPL-2.0 2 3 #include <linux/buildid.h> 4 #include <linux/elf.h> 5 #include <linux/pagemap.h> 6 7 #define BUILD_ID 3 8 /* 9 * Parse build id from the note segment. This logic can be shared between 10 * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are 11 * identical. 12 */ 13 static inline int parse_build_id(void *page_addr, 14 unsigned char *build_id, 15 __u32 *size, 16 void *note_start, 17 Elf32_Word note_size) 18 { 19 Elf32_Word note_offs = 0, new_offs; 20 21 /* check for overflow */ 22 if (note_start < page_addr || note_start + note_size < note_start) 23 return -EINVAL; 24 25 /* only supports note that fits in the first page */ 26 if (note_start + note_size > page_addr + PAGE_SIZE) 27 return -EINVAL; 28 29 while (note_offs + sizeof(Elf32_Nhdr) < note_size) { 30 Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs); 31 32 if (nhdr->n_type == BUILD_ID && 33 nhdr->n_namesz == sizeof("GNU") && 34 nhdr->n_descsz > 0 && 35 nhdr->n_descsz <= BUILD_ID_SIZE_MAX) { 36 memcpy(build_id, 37 note_start + note_offs + 38 ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr), 39 nhdr->n_descsz); 40 memset(build_id + nhdr->n_descsz, 0, 41 BUILD_ID_SIZE_MAX - nhdr->n_descsz); 42 if (size) 43 *size = nhdr->n_descsz; 44 return 0; 45 } 46 new_offs = note_offs + sizeof(Elf32_Nhdr) + 47 ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4); 48 if (new_offs <= note_offs) /* overflow */ 49 break; 50 note_offs = new_offs; 51 } 52 return -EINVAL; 53 } 54 55 /* Parse build ID from 32-bit ELF */ 56 static int get_build_id_32(void *page_addr, unsigned char *build_id, 57 __u32 *size) 58 { 59 Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr; 60 Elf32_Phdr *phdr; 61 int i; 62 63 /* only supports phdr that fits in one page */ 64 if (ehdr->e_phnum > 65 (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr)) 66 return -EINVAL; 67 68 phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr)); 69 70 for (i = 0; i < ehdr->e_phnum; ++i) { 71 if (phdr[i].p_type == PT_NOTE && 72 !parse_build_id(page_addr, build_id, size, 73 page_addr + phdr[i].p_offset, 74 phdr[i].p_filesz)) 75 return 0; 76 } 77 return -EINVAL; 78 } 79 80 /* Parse build ID from 64-bit ELF */ 81 static int get_build_id_64(void *page_addr, unsigned char *build_id, 82 __u32 *size) 83 { 84 Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr; 85 Elf64_Phdr *phdr; 86 int i; 87 88 /* only supports phdr that fits in one page */ 89 if (ehdr->e_phnum > 90 (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr)) 91 return -EINVAL; 92 93 phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr)); 94 95 for (i = 0; i < ehdr->e_phnum; ++i) { 96 if (phdr[i].p_type == PT_NOTE && 97 !parse_build_id(page_addr, build_id, size, 98 page_addr + phdr[i].p_offset, 99 phdr[i].p_filesz)) 100 return 0; 101 } 102 return -EINVAL; 103 } 104 105 /* 106 * Parse build ID of ELF file mapped to vma 107 * @vma: vma object 108 * @build_id: buffer to store build id, at least BUILD_ID_SIZE long 109 * @size: returns actual build id size in case of success 110 * 111 * Returns 0 on success, otherwise error (< 0). 112 */ 113 int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id, 114 __u32 *size) 115 { 116 Elf32_Ehdr *ehdr; 117 struct page *page; 118 void *page_addr; 119 int ret; 120 121 /* only works for page backed storage */ 122 if (!vma->vm_file) 123 return -EINVAL; 124 125 page = find_get_page(vma->vm_file->f_mapping, 0); 126 if (!page) 127 return -EFAULT; /* page not mapped */ 128 129 ret = -EINVAL; 130 page_addr = kmap_atomic(page); 131 ehdr = (Elf32_Ehdr *)page_addr; 132 133 /* compare magic x7f "ELF" */ 134 if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0) 135 goto out; 136 137 /* only support executable file and shared object file */ 138 if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN) 139 goto out; 140 141 if (ehdr->e_ident[EI_CLASS] == ELFCLASS32) 142 ret = get_build_id_32(page_addr, build_id, size); 143 else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64) 144 ret = get_build_id_64(page_addr, build_id, size); 145 out: 146 kunmap_atomic(page_addr); 147 put_page(page); 148 return ret; 149 } 150