With this commit, image validation can be enforced, as UEFI specification section 32.5 describes, if CONFIG_EFI_SECURE_BOOT is enabled.
Currently we support * authentication based on db and dbx, so dbx-validated image will always be rejected. * following signature types: EFI_CERT_SHA256_GUID (SHA256 digest for unsigned images) EFI_CERT_X509_GUID (x509 certificate for signed images) Timestamp-based certificate revocation is not supported here.
Internally, authentication data is stored in one of certificates tables of PE image (See efi_image_parse()) and will be verified by efi_image_authenticate() before loading a given image.
It seems that UEFI specification defines the verification process in a bit ambiguous way. I tried to implement it as closely to as EDK2 does.
Signed-off-by: AKASHI Takahiro takahiro.akashi@linaro.org --- include/efi_loader.h | 7 +- lib/efi_loader/efi_boottime.c | 2 +- lib/efi_loader/efi_image_loader.c | 454 +++++++++++++++++++++++++++++- 3 files changed, 449 insertions(+), 14 deletions(-)
diff --git a/include/efi_loader.h b/include/efi_loader.h index 1f88caf86709..e12b49098fb0 100644 --- a/include/efi_loader.h +++ b/include/efi_loader.h @@ -11,6 +11,7 @@ #include <common.h> #include <part_efi.h> #include <efi_api.h> +#include <pe.h>
static inline int guidcmp(const void *g1, const void *g2) { @@ -398,7 +399,8 @@ efi_status_t efi_set_watchdog(unsigned long timeout); /* Called from places to check whether a timer expired */ void efi_timer_check(void); /* PE loader implementation */ -efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, void *efi, +efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, + void *efi, size_t efi_size, struct efi_loaded_image *loaded_image_info); /* Called once to store the pristine gd pointer */ void efi_save_gd(void); @@ -726,6 +728,9 @@ void efi_sigstore_free(struct efi_signature_store *sigstore); struct efi_signature_store *efi_sigstore_parse_sigdb(u16 *name);
bool efi_secure_boot_enabled(void); + +bool efi_image_parse(void *efi, size_t len, struct efi_image_regions **regp, + WIN_CERTIFICATE **auth, size_t *auth_len); #endif /* CONFIG_EFI_SECURE_BOOT */
#else /* CONFIG_IS_ENABLED(EFI_LOADER) */ diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c index 493d906c641d..311681764034 100644 --- a/lib/efi_loader/efi_boottime.c +++ b/lib/efi_loader/efi_boottime.c @@ -1879,7 +1879,7 @@ efi_status_t EFIAPI efi_load_image(bool boot_policy, efi_dp_split_file_path(file_path, &dp, &fp); ret = efi_setup_loaded_image(dp, fp, image_obj, &info); if (ret == EFI_SUCCESS) - ret = efi_load_pe(*image_obj, dest_buffer, info); + ret = efi_load_pe(*image_obj, dest_buffer, source_size, info); if (!source_buffer) /* Release buffer to which file was loaded */ efi_free_pages((uintptr_t)dest_buffer, diff --git a/lib/efi_loader/efi_image_loader.c b/lib/efi_loader/efi_image_loader.c index 13541cfa7a28..939758e61e3c 100644 --- a/lib/efi_loader/efi_image_loader.c +++ b/lib/efi_loader/efi_image_loader.c @@ -9,7 +9,9 @@
#include <common.h> #include <efi_loader.h> +#include <malloc.h> #include <pe.h> +#include "../lib/crypto/pkcs7_parser.h"
const efi_guid_t efi_global_variable_guid = EFI_GLOBAL_VARIABLE_GUID; const efi_guid_t efi_guid_device_path = EFI_DEVICE_PATH_PROTOCOL_GUID; @@ -205,6 +207,367 @@ static void efi_set_code_and_data_type( } }
+#ifdef CONFIG_EFI_SECURE_BOOT +/** + * efi_image_parse - parse a PE image + * @efi: Pointer to image + * @len: Size of @efi + * @regs: Pointer to a list of regions + * @auth: Pointer to a pointer to authentication data in PE + * @auth_len: Size of @auth + * + * Parse image binary in PE32(+) format, assuming that sanity of PE image + * has been checked by a caller. + * On success, an address of authentication data in @efi and its size will + * be returned in @auth and @auth_len, respectively. + * + * Return: true on success, false on error + */ +bool efi_image_parse(void *efi, size_t len, struct efi_image_regions **regp, + WIN_CERTIFICATE **auth, size_t *auth_len) +{ + struct efi_image_regions *regs; + IMAGE_DOS_HEADER *dos; + IMAGE_NT_HEADERS32 *nt; + IMAGE_SECTION_HEADER *sections, **sorted; + int num_regions, num_sections, i, j; + int ctidx = IMAGE_DIRECTORY_ENTRY_SECURITY; + u32 align, size, authsz, authoff; + size_t bytes_hashed; + + dos = (void *)efi; + nt = (void *)(efi + dos->e_lfanew); + + /* + * Count maximum number of regions to be digested. + * We don't have to have an exact number here. + * See efi_image_region_add()'s in parsing below. + */ + num_regions = 3; /* for header */ + num_regions += nt->FileHeader.NumberOfSections; + num_regions++; /* for extra */ + + regs = calloc(sizeof(*regs) + sizeof(struct image_region) * num_regions, + 1); + if (!regs) + goto err; + regs->max = num_regions; + + /* + * Collect data regions for hash calculation + * 1. File headers + */ + if (nt->OptionalHeader.Magic == IMAGE_NT_OPTIONAL_HDR64_MAGIC) { + IMAGE_NT_HEADERS64 *nt64 = (void *)nt; + IMAGE_OPTIONAL_HEADER64 *opt = &nt64->OptionalHeader; + + /* Skip CheckSum */ + efi_image_region_add(regs, efi, &opt->CheckSum, 0); + if (nt64->OptionalHeader.NumberOfRvaAndSizes <= ctidx) { + efi_image_region_add(regs, + &opt->CheckSum + 1, + efi + opt->SizeOfHeaders, 0); + } else { + /* Skip Certificates Table */ + efi_image_region_add(regs, + &opt->CheckSum + 1, + &opt->DataDirectory[ctidx], 0); + efi_image_region_add(regs, + &opt->DataDirectory[ctidx] + 1, + efi + opt->SizeOfHeaders, 0); + } + + bytes_hashed = opt->SizeOfHeaders; + align = opt->FileAlignment; + authoff = opt->DataDirectory[ctidx].VirtualAddress; + authsz = opt->DataDirectory[ctidx].Size; + } else if (nt->OptionalHeader.Magic == IMAGE_NT_OPTIONAL_HDR32_MAGIC) { + IMAGE_OPTIONAL_HEADER32 *opt = &nt->OptionalHeader; + + efi_image_region_add(regs, efi, &opt->CheckSum, 0); + efi_image_region_add(regs, &opt->CheckSum + 1, + &opt->DataDirectory[ctidx], 0); + efi_image_region_add(regs, &opt->DataDirectory[ctidx] + 1, + efi + opt->SizeOfHeaders, 0); + + bytes_hashed = opt->SizeOfHeaders; + align = opt->FileAlignment; + authoff = opt->DataDirectory[ctidx].VirtualAddress; + authsz = opt->DataDirectory[ctidx].Size; + } else { + debug("%s: Invalid optional header magic %x\n", __func__, + nt->OptionalHeader.Magic); + goto err; + } + + /* 2. Sections */ + num_sections = nt->FileHeader.NumberOfSections; + sections = (void *)((uint8_t *)&nt->OptionalHeader + + nt->FileHeader.SizeOfOptionalHeader); + sorted = calloc(sizeof(IMAGE_SECTION_HEADER *), num_sections); + if (!sorted) { + debug("%s: Out of memory\n", __func__); + goto err; + } + + /* + * Make sure the section list is in ascending order. + * As we can assume that it is already ordered in most cases, + * the following code is optimized for this. + */ + for (sorted[0] = §ions[0], i = 1; i < num_sections; i++) { + if (sorted[i - 1]->VirtualAddress + <= sections[i].VirtualAddress) { + sorted[i] = §ions[i]; + } else { + if (i == 1) { + sorted[1] = sorted[0]; + sorted[0] = §ions[1]; + continue; + } + + sorted[i] = sorted[i - 1]; + for (j = i - 2; j >= 0; j--) { + if (!j || sorted[j]->VirtualAddress + <= sections[i].VirtualAddress) { + sorted[j + 1] = §ions[i]; + continue; + } else { + sorted[j + 1] = sorted[j]; + } + } + } + } + + for (i = 0; i < num_sections; i++) { + if (!sorted[i]->SizeOfRawData) + continue; + + size = (sorted[i]->SizeOfRawData + align - 1) & ~(align - 1); + efi_image_region_add(regs, efi + sorted[i]->PointerToRawData, + efi + sorted[i]->PointerToRawData + size, + 0); + debug("section[%d](%s): raw: 0x%x-0x%x, virt: %x-%x\n", + i, sorted[i]->Name, + sorted[i]->PointerToRawData, + sorted[i]->PointerToRawData + size, + sorted[i]->VirtualAddress, + sorted[i]->VirtualAddress + + sorted[i]->Misc.VirtualSize); + + bytes_hashed += size; + } + free(sorted); + + /* 3. Extra data excluding Certificates Table */ + if (bytes_hashed + authsz < len) { + debug("extra data for hash: %lu\n", + len - (bytes_hashed + authsz)); + efi_image_region_add(regs, efi + bytes_hashed, + efi + len - authsz, 0); + } + + /* Return Certificates Table */ + if (authsz) { + if (len < authoff + authsz) { + debug("%s: Size for auth too large: %u >= %zu\n", + __func__, authsz, len - authoff); + goto err; + } + if (authsz < sizeof(*auth)) { + debug("%s: Size for auth too small: %u < %zu\n", + __func__, authsz, sizeof(*auth)); + goto err; + } + *auth = efi + authoff; + *auth_len = authsz; + debug("WIN_CERTIFICATE: 0x%x, size: 0x%x\n", authoff, authsz); + } else { + *auth = NULL; + *auth_len = 0; + } + + *regp = regs; + + return true; + +err: + free(regs); + + return false; +} + +/** + * efi_image_unsigned_authenticate - authenticate unsigned image with + * SHA256 hash + * @regs: List of regions to be verified + * + * If an image is not signed, it doesn't have a signature. In this case, + * its message digest is calculated and it will be compared with one of + * hash values stored in signature databases. + * + * Return: true if authenticated, false if not + */ +static bool efi_image_unsigned_authenticate(struct efi_image_regions *regs) +{ + struct efi_signature_store *db = NULL, *dbx = NULL; + bool ret = false; + + dbx = efi_sigstore_parse_sigdb(L"dbx"); + if (!dbx) { + debug("Getting signature database(dbx) failed\n"); + goto out; + } + + db = efi_sigstore_parse_sigdb(L"db"); + if (!db) { + debug("Getting signature database(db) failed\n"); + goto out; + } + + /* try black-list first */ + if (efi_signature_verify_with_sigdb(regs, NULL, dbx, NULL)) { + debug("Image is not signed and rejected by "dbx"\n"); + goto out; + } + + /* try white-list */ + if (efi_signature_verify_with_sigdb(regs, NULL, db, NULL)) + ret = true; + else + debug("Image is not signed and not found in "db" or "dbx"\n"); + +out: + efi_sigstore_free(db); + efi_sigstore_free(dbx); + + return ret; +} + +/** + * efi_image_authenticate - verify a signature of signed image + * @efi: Pointer to image + * @len: Size of @efi + * + * A signed image should have its signature stored in a table of its PE header. + * So if an image is signed and only if if its signature is verified using + * signature databases, an image is authenticated. + * If an image is not signed, its validity is checked by using + * efi_image_unsigned_authenticated(). + * TODO: + * When AuditMode==0, if the image's signature is not found in + * the authorized database, or is found in the forbidden database, + * the image will not be started and instead, information about it + * will be placed in this table. + * When AuditMode==1, an EFI_IMAGE_EXECUTION_INFO element is created + * in the EFI_IMAGE_EXECUTION_INFO_TABLE for every certificate found + * in the certificate table of every image that is validated. + * + * Return: true if authenticated, false if not + */ +static bool efi_image_authenticate(void *efi, size_t len) +{ + struct efi_image_regions *regs = NULL; + WIN_CERTIFICATE *wincerts = NULL, *wincert; + size_t wincerts_len; + struct pkcs7_message *msg = NULL; + struct efi_signature_store *db = NULL, *dbx = NULL; + struct x509_certificate *cert = NULL; + bool ret = false; + + if (!efi_secure_boot_enabled()) + return true; + + if (!efi_image_parse(efi, len, ®s, &wincerts, + &wincerts_len)) { + debug("Parsing PE executable image failed\n"); + return false; + } + + if (!wincerts) { + /* The image is not signed */ + ret = efi_image_unsigned_authenticate(regs); + free(regs); + + return ret; + } + + /* + * verify signature using db and dbx + */ + db = efi_sigstore_parse_sigdb(L"db"); + if (!db) { + debug("Getting signature database(db) failed\n"); + goto err; + } + + dbx = efi_sigstore_parse_sigdb(L"dbx"); + if (!dbx) { + debug("Getting signature database(dbx) failed\n"); + goto err; + } + + /* go through WIN_CERTIFICATE list */ + for (wincert = wincerts; + (void *)wincert < (void *)wincerts + wincerts_len; + wincert = (void *)wincert + ALIGN(wincert->dwLength, 8)) { + if (wincert->dwLength < sizeof(*wincert)) { + debug("%s: dwLength too small: %u < %zu\n", + __func__, wincert->dwLength, sizeof(*wincert)); + goto err; + } + msg = pkcs7_parse_message((void *)wincert + sizeof(*wincert), + wincert->dwLength - sizeof(*wincert)); + if (!msg) { + debug("Parsing image's signature failed\n"); + goto err; + } + + /* try black-list first */ + if (efi_signature_verify_with_sigdb(regs, msg, dbx, NULL)) { + debug("Signature was rejected by "dbx"\n"); + goto err; + } + + if (!efi_signature_verify_signers(msg, dbx)) { + debug("Signer was rejected by "dbx"\n"); + goto err; + } else { + ret = true; + } + + /* try white-list */ + if (!efi_signature_verify_with_sigdb(regs, msg, db, &cert)) { + debug("Verifying signature with "db" failed\n"); + goto err; + } else { + ret = true; + } + + if (!efi_signature_verify_cert(cert, dbx)) { + debug("Certificate was rejected by "dbx"\n"); + goto err; + } else { + ret = true; + } + } + +err: + x509_free_certificate(cert); + efi_sigstore_free(db); + efi_sigstore_free(dbx); + pkcs7_free_message(msg); + free(regs); + + return ret; +} +#else +static bool efi_image_authenticate(void *efi, size_t len) +{ + return true; +} +#endif /* CONFIG_EFI_SECURE_BOOT */ + /** * efi_load_pe() - relocate EFI binary * @@ -216,7 +579,8 @@ static void efi_set_code_and_data_type( * @loaded_image_info: loaded image protocol * Return: status code */ -efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, void *efi, +efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, + void *efi, size_t efi_size, struct efi_loaded_image *loaded_image_info) { IMAGE_NT_HEADERS32 *nt; @@ -231,17 +595,57 @@ efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, void *efi, uint64_t image_base; unsigned long virt_size = 0; int supported = 0; + void *new_efi = NULL; + size_t new_efi_size; + efi_status_t ret; + + /* + * Size must be 8-byte aligned and the trailing bytes must be + * zero'ed. Otherwise hash value may be incorrect. + */ + if (efi_size & 0x7) { + new_efi_size = (efi_size + 0x7) & ~0x7ULL; + new_efi = calloc(new_efi_size, 1); + if (!new_efi) + return EFI_OUT_OF_RESOURCES; + memcpy(new_efi, efi, efi_size); + efi = new_efi; + efi_size = new_efi_size; + } + + /* Sanity check for a file header */ + if (efi_size < sizeof(*dos)) { + printf("%s: Truncated DOS Header\n", __func__); + ret = EFI_LOAD_ERROR; + goto err; + }
dos = efi; if (dos->e_magic != IMAGE_DOS_SIGNATURE) { printf("%s: Invalid DOS Signature\n", __func__); - return EFI_LOAD_ERROR; + ret = EFI_LOAD_ERROR; + goto err; + } + + /* assume sizeof(IMAGE_NT_HEADERS32) <= sizeof(IMAGE_NT_HEADERS64) */ + if (efi_size < dos->e_lfanew + sizeof(IMAGE_NT_HEADERS32)) { + printf("%s: Invalid offset for Extended Header\n", __func__); + ret = EFI_LOAD_ERROR; + goto err; }
nt = (void *) ((char *)efi + dos->e_lfanew); + if ((nt->OptionalHeader.Magic == IMAGE_NT_OPTIONAL_HDR64_MAGIC) && + (efi_size < dos->e_lfanew + sizeof(IMAGE_NT_HEADERS64))) { + printf("%s: Invalid offset for Extended Header\n", __func__); + ret = EFI_LOAD_ERROR; + goto err; + } + if (nt->Signature != IMAGE_NT_SIGNATURE) { printf("%s: Invalid NT Signature\n", __func__); - return EFI_LOAD_ERROR; + ret = EFI_LOAD_ERROR; + goto err; }
for (i = 0; machines[i]; i++) @@ -253,14 +657,29 @@ efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, void *efi, if (!supported) { printf("%s: Machine type 0x%04x is not supported\n", __func__, nt->FileHeader.Machine); - return EFI_LOAD_ERROR; + ret = EFI_LOAD_ERROR; + goto err; }
- /* Calculate upper virtual address boundary */ num_sections = nt->FileHeader.NumberOfSections; sections = (void *)&nt->OptionalHeader + nt->FileHeader.SizeOfOptionalHeader;
+ if (efi_size < ((void *)sections + sizeof(sections[0]) * num_sections + - efi)) { + printf("%s: Invalid number of sections: %d\n", + __func__, num_sections); + ret = EFI_LOAD_ERROR; + goto err; + } + + /* Authenticate an image */ + if (!efi_image_authenticate(efi, efi_size)) { + ret = EFI_ACCESS_DENIED; + goto err; + } + + /* Calculate upper virtual address boundary */ for (i = num_sections - 1; i >= 0; i--) { IMAGE_SECTION_HEADER *sec = §ions[i]; virt_size = max_t(unsigned long, virt_size, @@ -279,7 +698,8 @@ efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, void *efi, if (!efi_reloc) { printf("%s: Could not allocate %lu bytes\n", __func__, virt_size); - return EFI_OUT_OF_RESOURCES; + ret = EFI_OUT_OF_RESOURCES; + goto err; } handle->entry = efi_reloc + opt->AddressOfEntryPoint; rel_size = opt->DataDirectory[rel_idx].Size; @@ -295,7 +715,8 @@ efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, void *efi, if (!efi_reloc) { printf("%s: Could not allocate %lu bytes\n", __func__, virt_size); - return EFI_OUT_OF_RESOURCES; + ret = EFI_OUT_OF_RESOURCES; + goto err; } handle->entry = efi_reloc + opt->AddressOfEntryPoint; rel_size = opt->DataDirectory[rel_idx].Size; @@ -304,13 +725,16 @@ efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, void *efi, } else { printf("%s: Invalid optional header magic %x\n", __func__, nt->OptionalHeader.Magic); - return EFI_LOAD_ERROR; + ret = EFI_LOAD_ERROR; + goto err; }
/* Copy PE headers */ - memcpy(efi_reloc, efi, sizeof(*dos) + sizeof(*nt) - + nt->FileHeader.SizeOfOptionalHeader - + num_sections * sizeof(IMAGE_SECTION_HEADER)); + memcpy(efi_reloc, efi, + sizeof(*dos) + + sizeof(*nt) + + nt->FileHeader.SizeOfOptionalHeader + + num_sections * sizeof(IMAGE_SECTION_HEADER));
/* Load sections into RAM */ for (i = num_sections - 1; i >= 0; i--) { @@ -327,7 +751,8 @@ efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, void *efi, (unsigned long)image_base) != EFI_SUCCESS) { efi_free_pages((uintptr_t) efi_reloc, (virt_size + EFI_PAGE_MASK) >> EFI_PAGE_SHIFT); - return EFI_LOAD_ERROR; + ret = EFI_LOAD_ERROR; + goto err; }
/* Flush cache */ @@ -340,4 +765,9 @@ efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, void *efi, loaded_image_info->image_size = virt_size;
return EFI_SUCCESS; + +err: + free(new_efi); + + return ret; }