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1// SPDX-License-Identifier: GPL-2.02 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#include <linux/secretmem.h>9 10#define BUILD_ID 311 12#define MAX_PHDR_CNT 25613 14struct freader {15 void *buf;16 u32 buf_sz;17 int err;18 union {19 struct {20 struct file *file;21 struct folio *folio;22 void *addr;23 loff_t folio_off;24 bool may_fault;25 };26 struct {27 const char *data;28 u64 data_sz;29 };30 };31};32 33static void freader_init_from_file(struct freader *r, void *buf, u32 buf_sz,34 struct file *file, bool may_fault)35{36 memset(r, 0, sizeof(*r));37 r->buf = buf;38 r->buf_sz = buf_sz;39 r->file = file;40 r->may_fault = may_fault;41}42 43static void freader_init_from_mem(struct freader *r, const char *data, u64 data_sz)44{45 memset(r, 0, sizeof(*r));46 r->data = data;47 r->data_sz = data_sz;48}49 50static void freader_put_folio(struct freader *r)51{52 if (!r->folio)53 return;54 kunmap_local(r->addr);55 folio_put(r->folio);56 r->folio = NULL;57}58 59static HWJS_SUSPENDS int freader_get_folio(struct freader *r, loff_t file_off)60{61 /* check if we can just reuse current folio */62 if (r->folio && file_off >= r->folio_off &&63 file_off < r->folio_off + folio_size(r->folio))64 return 0;65 66 freader_put_folio(r);67 68 /* reject secretmem folios created with memfd_secret() */69 if (secretmem_mapping(r->file->f_mapping))70 return -EFAULT;71 72 r->folio = filemap_get_folio(r->file->f_mapping, file_off >> PAGE_SHIFT);73 74 /* if sleeping is allowed, wait for the page, if necessary */75 if (r->may_fault && (IS_ERR(r->folio) || !folio_test_uptodate(r->folio))) {76 filemap_invalidate_lock_shared(r->file->f_mapping);77 r->folio = read_cache_folio(r->file->f_mapping, file_off >> PAGE_SHIFT,78 NULL, r->file);79 filemap_invalidate_unlock_shared(r->file->f_mapping);80 }81 82 if (IS_ERR(r->folio) || !folio_test_uptodate(r->folio)) {83 if (!IS_ERR(r->folio))84 folio_put(r->folio);85 r->folio = NULL;86 return -EFAULT;87 }88 89 r->folio_off = folio_pos(r->folio);90 r->addr = kmap_local_folio(r->folio, 0);91 92 return 0;93}94 95static HWJS_SUSPENDS const void *freader_fetch(struct freader *r, loff_t file_off, size_t sz)96{97 size_t folio_sz;98 99 /* provided internal temporary buffer should be sized correctly */100 if (WARN_ON(r->buf && sz > r->buf_sz)) {101 r->err = -E2BIG;102 return NULL;103 }104 105 if (unlikely(file_off + sz < file_off)) {106 r->err = -EOVERFLOW;107 return NULL;108 }109 110 /* working with memory buffer is much more straightforward */111 if (!r->buf) {112 if (file_off + sz > r->data_sz) {113 r->err = -ERANGE;114 return NULL;115 }116 return r->data + file_off;117 }118 119 /* fetch or reuse folio for given file offset */120 r->err = freader_get_folio(r, file_off);121 if (r->err)122 return NULL;123 124 /* if requested data is crossing folio boundaries, we have to copy125 * everything into our local buffer to keep a simple linear memory126 * access interface127 */128 folio_sz = folio_size(r->folio);129 if (file_off + sz > r->folio_off + folio_sz) {130 int part_sz = r->folio_off + folio_sz - file_off;131 132 /* copy the part that resides in the current folio */133 memcpy(r->buf, r->addr + (file_off - r->folio_off), part_sz);134 135 /* fetch next folio */136 r->err = freader_get_folio(r, r->folio_off + folio_sz);137 if (r->err)138 return NULL;139 140 /* copy the rest of requested data */141 memcpy(r->buf + part_sz, r->addr, sz - part_sz);142 143 return r->buf;144 }145 146 /* if data fits in a single folio, just return direct pointer */147 return r->addr + (file_off - r->folio_off);148}149 150static void freader_cleanup(struct freader *r)151{152 if (!r->buf)153 return; /* non-file-backed mode */154 155 freader_put_folio(r);156}157 158/*159 * Parse build id from the note segment. This logic can be shared between160 * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are161 * identical.162 */163static HWJS_SUSPENDS int parse_build_id(struct freader *r, unsigned char *build_id, __u32 *size,164 loff_t note_off, Elf32_Word note_size)165{166 const char note_name[] = "GNU";167 const size_t note_name_sz = sizeof(note_name);168 u32 build_id_off, new_off, note_end, name_sz, desc_sz;169 const Elf32_Nhdr *nhdr;170 const char *data;171 172 if (check_add_overflow(note_off, note_size, ¬e_end))173 return -EINVAL;174 175 while (note_end - note_off > sizeof(Elf32_Nhdr) + note_name_sz) {176 nhdr = freader_fetch(r, note_off, sizeof(Elf32_Nhdr) + note_name_sz);177 if (!nhdr)178 return r->err;179 180 name_sz = READ_ONCE(nhdr->n_namesz);181 desc_sz = READ_ONCE(nhdr->n_descsz);182 183 new_off = note_off + sizeof(Elf32_Nhdr);184 if (check_add_overflow(new_off, ALIGN(name_sz, 4), &new_off) ||185 check_add_overflow(new_off, ALIGN(desc_sz, 4), &new_off) ||186 new_off > note_end)187 break;188 189 if (nhdr->n_type == BUILD_ID &&190 name_sz == note_name_sz &&191 memcmp(nhdr + 1, note_name, note_name_sz) == 0 &&192 desc_sz > 0 && desc_sz <= BUILD_ID_SIZE_MAX) {193 build_id_off = note_off + sizeof(Elf32_Nhdr) + ALIGN(note_name_sz, 4);194 195 /* freader_fetch() will invalidate nhdr pointer */196 data = freader_fetch(r, build_id_off, desc_sz);197 if (!data)198 return r->err;199 200 memcpy(build_id, data, desc_sz);201 memset(build_id + desc_sz, 0, BUILD_ID_SIZE_MAX - desc_sz);202 if (size)203 *size = desc_sz;204 return 0;205 }206 207 note_off = new_off;208 }209 210 return -EINVAL;211}212 213/* Parse build ID from 32-bit ELF */214static HWJS_SUSPENDS int get_build_id_32(struct freader *r, unsigned char *build_id, __u32 *size)215{216 const Elf32_Ehdr *ehdr;217 const Elf32_Phdr *phdr;218 __u32 phnum, phoff, i;219 220 ehdr = freader_fetch(r, 0, sizeof(Elf32_Ehdr));221 if (!ehdr)222 return r->err;223 224 /* subsequent freader_fetch() calls invalidate pointers, so remember locally */225 phnum = READ_ONCE(ehdr->e_phnum);226 phoff = READ_ONCE(ehdr->e_phoff);227 228 /* set upper bound on amount of segments (phdrs) we iterate */229 if (phnum > MAX_PHDR_CNT)230 phnum = MAX_PHDR_CNT;231 232 /* check that phoff is not large enough to cause an overflow */233 if (phoff + phnum * sizeof(Elf32_Phdr) < phoff)234 return -EINVAL;235 236 for (i = 0; i < phnum; ++i) {237 phdr = freader_fetch(r, phoff + i * sizeof(Elf32_Phdr), sizeof(Elf32_Phdr));238 if (!phdr)239 return r->err;240 241 if (phdr->p_type == PT_NOTE &&242 !parse_build_id(r, build_id, size, READ_ONCE(phdr->p_offset),243 READ_ONCE(phdr->p_filesz)))244 return 0;245 }246 return -EINVAL;247}248 249/* Parse build ID from 64-bit ELF */250static HWJS_SUSPENDS int get_build_id_64(struct freader *r, unsigned char *build_id, __u32 *size)251{252 const Elf64_Ehdr *ehdr;253 const Elf64_Phdr *phdr;254 __u32 phnum, i;255 __u64 phoff;256 257 ehdr = freader_fetch(r, 0, sizeof(Elf64_Ehdr));258 if (!ehdr)259 return r->err;260 261 /* subsequent freader_fetch() calls invalidate pointers, so remember locally */262 phnum = READ_ONCE(ehdr->e_phnum);263 phoff = READ_ONCE(ehdr->e_phoff);264 265 /* set upper bound on amount of segments (phdrs) we iterate */266 if (phnum > MAX_PHDR_CNT)267 phnum = MAX_PHDR_CNT;268 269 /* check that phoff is not large enough to cause an overflow */270 if (phoff + phnum * sizeof(Elf64_Phdr) < phoff)271 return -EINVAL;272 273 for (i = 0; i < phnum; ++i) {274 phdr = freader_fetch(r, phoff + i * sizeof(Elf64_Phdr), sizeof(Elf64_Phdr));275 if (!phdr)276 return r->err;277 278 if (phdr->p_type == PT_NOTE &&279 !parse_build_id(r, build_id, size, READ_ONCE(phdr->p_offset),280 READ_ONCE(phdr->p_filesz)))281 return 0;282 }283 284 return -EINVAL;285}286 287/* enough for Elf64_Ehdr, Elf64_Phdr, and all the smaller requests */288#define MAX_FREADER_BUF_SZ 64289 290static int __build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,291 __u32 *size, bool may_fault)292{293 const Elf32_Ehdr *ehdr;294 struct freader r;295 char buf[MAX_FREADER_BUF_SZ];296 int ret;297 298 /* only works for page backed storage */299 if (!vma->vm_file)300 return -EINVAL;301 302 freader_init_from_file(&r, buf, sizeof(buf), vma->vm_file, may_fault);303 304 /* fetch first 18 bytes of ELF header for checks */305 ehdr = freader_fetch(&r, 0, offsetofend(Elf32_Ehdr, e_type));306 if (!ehdr) {307 ret = r.err;308 goto out;309 }310 311 ret = -EINVAL;312 313 /* compare magic x7f "ELF" */314 if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)315 goto out;316 317 /* only support executable file and shared object file */318 if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)319 goto out;320 321 if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)322 ret = get_build_id_32(&r, build_id, size);323 else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)324 ret = get_build_id_64(&r, build_id, size);325out:326 freader_cleanup(&r);327 return ret;328}329 330/*331 * Parse build ID of ELF file mapped to vma332 * @vma: vma object333 * @build_id: buffer to store build id, at least BUILD_ID_SIZE long334 * @size: returns actual build id size in case of success335 *336 * Assumes no page fault can be taken, so if relevant portions of ELF file are337 * not already paged in, fetching of build ID fails.338 *339 * Return: 0 on success; negative error, otherwise340 */341int build_id_parse_nofault(struct vm_area_struct *vma, unsigned char *build_id, __u32 *size)342{343 return __build_id_parse(vma, build_id, size, false /* !may_fault */);344}345 346/*347 * Parse build ID of ELF file mapped to VMA348 * @vma: vma object349 * @build_id: buffer to store build id, at least BUILD_ID_SIZE long350 * @size: returns actual build id size in case of success351 *352 * Assumes faultable context and can cause page faults to bring in file data353 * into page cache.354 *355 * Return: 0 on success; negative error, otherwise356 */357int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id, __u32 *size)358{359 return __build_id_parse(vma, build_id, size, true /* may_fault */);360}361 362/**363 * build_id_parse_buf - Get build ID from a buffer364 * @buf: ELF note section(s) to parse365 * @buf_size: Size of @buf in bytes366 * @build_id: Build ID parsed from @buf, at least BUILD_ID_SIZE_MAX long367 *368 * Return: 0 on success, -EINVAL otherwise369 */370int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size)371{372 struct freader r;373 int err;374 375 freader_init_from_mem(&r, buf, buf_size);376 377 err = parse_build_id(&r, build_id, NULL, 0, buf_size);378 379 freader_cleanup(&r);380 return err;381}382 383#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) || IS_ENABLED(CONFIG_VMCORE_INFO)384unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX] __ro_after_init;385 386/**387 * init_vmlinux_build_id - Compute and stash the running kernel's build ID388 */389void __init init_vmlinux_build_id(void)390{391 extern const void __start_notes;392 extern const void __stop_notes;393 unsigned int size = &__stop_notes - &__start_notes;394 395 build_id_parse_buf(&__start_notes, vmlinux_build_id, size);396}397#endif398