diff options
Diffstat (limited to 'src/pcrlock/pehash.c')
| -rw-r--r-- | src/pcrlock/pehash.c | 246 |
1 files changed, 246 insertions, 0 deletions
diff --git a/src/pcrlock/pehash.c b/src/pcrlock/pehash.c new file mode 100644 index 0000000..06d1f6a --- /dev/null +++ b/src/pcrlock/pehash.c @@ -0,0 +1,246 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <sys/stat.h> +#include <unistd.h> + +#include "alloc-util.h" +#include "hexdecoct.h" +#include "pe-binary.h" +#include "pehash.h" +#include "sort-util.h" +#include "stat-util.h" +#include "string-table.h" + +/* Implements: + * + * https://download.microsoft.com/download/9/c/5/9c5b2167-8017-4bae-9fde-d599bac8184a/authenticode_pe.docx + * → Section "Calculating the PE Image Hash" + */ + +#define IMAGE_DATA_DIRECTORY_INDEX_CERTIFICATION_TABLE 4U + +static int hash_file(int fd, EVP_MD_CTX *md_ctx, uint64_t offset, uint64_t size) { + uint8_t buffer[64*1024]; + + log_debug("Hashing %" PRIu64 " @ %" PRIu64 " → %" PRIu64, size, offset, offset + size); + + while (size > 0) { + size_t m = MIN(size, sizeof(buffer)); + ssize_t n; + + n = pread(fd, buffer, m, offset); + if (n < 0) + return log_debug_errno(errno, "Failed to read file for hashing: %m"); + if ((size_t) n != m) + return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG), "Short read while hashing."); + + if (EVP_DigestUpdate(md_ctx, buffer, m) != 1) + return log_debug_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "Unable to hash data."); + + offset += m; + size -= m; + } + + return 0; +} + +static int section_offset_cmp(const IMAGE_SECTION_HEADER *a, const IMAGE_SECTION_HEADER *b) { + return CMP(ASSERT_PTR(a)->PointerToRawData, ASSERT_PTR(b)->PointerToRawData); +} + +int pe_hash(int fd, + const EVP_MD *md, + void **ret_hash, + size_t *ret_hash_size) { + + _cleanup_(EVP_MD_CTX_freep) EVP_MD_CTX *mdctx = NULL; + _cleanup_free_ IMAGE_SECTION_HEADER *sections = NULL; + _cleanup_free_ IMAGE_DOS_HEADER *dos_header = NULL; + _cleanup_free_ PeHeader *pe_header = NULL; + const IMAGE_DATA_DIRECTORY *certificate_table; + struct stat st; + uint64_t p, q; + int r; + + assert(fd >= 0); + assert(md); + assert(ret_hash_size); + assert(ret_hash); + + if (fstat(fd, &st) < 0) + return log_debug_errno(errno, "Failed to stat file: %m"); + r = stat_verify_regular(&st); + if (r < 0) + return log_debug_errno(r, "Not a regular file: %m"); + + r = pe_load_headers(fd, &dos_header, &pe_header); + if (r < 0) + return r; + + r = pe_load_sections(fd, dos_header, pe_header, §ions); + if (r < 0) + return r; + + certificate_table = pe_header_get_data_directory(pe_header, IMAGE_DATA_DIRECTORY_INDEX_CERTIFICATION_TABLE); + if (!certificate_table) + return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG), "File lacks certificate table."); + + mdctx = EVP_MD_CTX_new(); + if (!mdctx) + return log_oom_debug(); + + if (EVP_DigestInit_ex(mdctx, md, NULL) != 1) + return log_debug_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "Failed to allocate message digest."); + + /* Everything from beginning of file to CheckSum field in PE header */ + p = (uint64_t) dos_header->e_lfanew + + offsetof(PeHeader, optional.CheckSum); + r = hash_file(fd, mdctx, 0, p); + if (r < 0) + return r; + p += sizeof(le32_t); + + /* Everything between the CheckSum field and the Image Data Directory Entry for the Certification Table */ + q = (uint64_t) dos_header->e_lfanew + + PE_HEADER_OPTIONAL_FIELD_OFFSET(pe_header, DataDirectory[IMAGE_DATA_DIRECTORY_INDEX_CERTIFICATION_TABLE]); + r = hash_file(fd, mdctx, p, q - p); + if (r < 0) + return r; + q += sizeof(IMAGE_DATA_DIRECTORY); + + /* The rest of the header + the section table */ + p = pe_header->optional.SizeOfHeaders; + if (p < q) + return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG), "SizeOfHeaders too short."); + r = hash_file(fd, mdctx, q, p - q); + if (r < 0) + return r; + + /* Sort by location in file */ + typesafe_qsort(sections, pe_header->pe.NumberOfSections, section_offset_cmp); + + FOREACH_ARRAY(section, sections, pe_header->pe.NumberOfSections) { + r = hash_file(fd, mdctx, section->PointerToRawData, section->SizeOfRawData); + if (r < 0) + return r; + + p += section->SizeOfRawData; + } + + if ((uint64_t) st.st_size > p) { + + if (st.st_size - p < certificate_table->Size) + return log_debug_errno(errno, "No space for certificate table, refusing."); + + r = hash_file(fd, mdctx, p, st.st_size - p - certificate_table->Size); + if (r < 0) + return r; + } + + int hsz = EVP_MD_CTX_size(mdctx); + if (hsz < 0) + return log_debug_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "Failed to get hash size."); + + unsigned hash_size = (unsigned) hsz; + _cleanup_free_ void *hash = malloc(hsz); + if (!hash) + return log_oom_debug(); + + if (EVP_DigestFinal_ex(mdctx, hash, &hash_size) != 1) + return log_debug_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "Failed to finalize hash function."); + + assert(hash_size == (unsigned) hsz); + + *ret_hash = TAKE_PTR(hash); + *ret_hash_size = hash_size; + + return 0; +} + +typedef void* SectionHashArray[_UNIFIED_SECTION_MAX]; + +static void section_hash_array_done(SectionHashArray *array) { + assert(array); + + for (size_t i = 0; i < _UNIFIED_SECTION_MAX; i++) + free((*array)[i]); +} + +int uki_hash(int fd, + const EVP_MD *md, + void* ret_hashes[static _UNIFIED_SECTION_MAX], + size_t *ret_hash_size) { + + _cleanup_(section_hash_array_done) SectionHashArray hashes = {}; + _cleanup_free_ IMAGE_SECTION_HEADER *sections = NULL; + _cleanup_free_ IMAGE_DOS_HEADER *dos_header = NULL; + _cleanup_free_ PeHeader *pe_header = NULL; + int r; + + assert(fd >= 0); + assert(ret_hashes); + assert(ret_hash_size); + + r = pe_load_headers(fd, &dos_header, &pe_header); + if (r < 0) + return r; + + r = pe_load_sections(fd, dos_header, pe_header, §ions); + if (r < 0) + return r; + + int hsz = EVP_MD_size(md); + if (hsz < 0) + return log_debug_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "Failed to get hash size."); + + FOREACH_ARRAY(section, sections, pe_header->pe.NumberOfSections) { + _cleanup_(EVP_MD_CTX_freep) EVP_MD_CTX *mdctx = NULL; + _cleanup_free_ char *n = NULL; + ssize_t i; + + n = memdup_suffix0(section->Name, sizeof(section->Name)); + if (!n) + return log_oom_debug(); + + i = string_table_lookup(unified_sections, _UNIFIED_SECTION_MAX, n); + if (i < 0) + continue; + + if (hashes[i]) + return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG), "Duplicate section"); + + mdctx = EVP_MD_CTX_new(); + if (!mdctx) + return log_oom_debug(); + + if (EVP_DigestInit_ex(mdctx, md, NULL) != 1) + return log_debug_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "Failed to allocate message digest."); + + r = hash_file(fd, mdctx, section->PointerToRawData, section->VirtualSize); + if (r < 0) + return r; + + hashes[i] = malloc(hsz); + if (!hashes[i]) + return log_oom_debug(); + + unsigned hash_size = (unsigned) hsz; + if (EVP_DigestFinal_ex(mdctx, hashes[i], &hash_size) != 1) + return log_debug_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "Failed to finalize hash function."); + + assert(hash_size == (unsigned) hsz); + + if (DEBUG_LOGGING) { + _cleanup_free_ char *hs = NULL; + + hs = hexmem(hashes[i], hsz); + log_debug("Section %s with %s is %s.", n, EVP_MD_name(md), strna(hs)); + } + } + + memcpy(ret_hashes, hashes, sizeof(hashes)); + zero(hashes); + *ret_hash_size = (unsigned) hsz; + + return 0; +} |