[v3,08/16] efi_loader: image_loader: support image authentication
diff mbox series

Message ID 20191209060056.32426-9-takahiro.akashi@linaro.org
State Superseded
Delegated to: Heinrich Schuchardt
Headers show
Series
  • efi_loader: add secure boot support
Related show

Commit Message

AKASHI Takahiro Dec. 9, 2019, 6 a.m. UTC
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(-)

Patch
diff mbox series

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] = &sections[0], i = 1; i < num_sections; i++) {
+		if (sorted[i - 1]->VirtualAddress
+				<= sections[i].VirtualAddress) {
+			sorted[i] = &sections[i];
+		} else {
+			if (i == 1) {
+				sorted[1] = sorted[0];
+				sorted[0] = &sections[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] = &sections[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, &regs, &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 = &sections[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;
 }