[PATCH v3 08/16] efi_loader: image_loader: support image authentication
AKASHI Takahiro
takahiro.akashi at linaro.org
Mon Dec 9 07:00:48 CET 2019
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 at 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;
}
--
2.24.0
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