efi_loader: image_loader: support image authentication

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>
This commit is contained in:
AKASHI Takahiro 2020-04-14 11:51:44 +09:00 committed by Heinrich Schuchardt
parent 8353516f4a
commit 4540dabdca
3 changed files with 469 additions and 16 deletions

View file

@ -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)
{
@ -263,6 +264,11 @@ struct efi_object {
enum efi_object_type type;
};
enum efi_image_auth_status {
EFI_IMAGE_AUTH_FAILED = 0,
EFI_IMAGE_AUTH_PASSED,
};
/**
* struct efi_loaded_image_obj - handle of a loaded image
*
@ -282,6 +288,7 @@ struct efi_loaded_image_obj {
EFIAPI efi_status_t (*entry)(efi_handle_t image_handle,
struct efi_system_table *st);
u16 image_type;
enum efi_image_auth_status auth_status;
};
/**
@ -415,7 +422,8 @@ 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);
@ -756,6 +764,9 @@ 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) */

View file

@ -1882,12 +1882,12 @@ 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,
efi_size_in_pages(source_size));
if (ret == EFI_SUCCESS) {
if (ret == EFI_SUCCESS || ret == EFI_SECURITY_VIOLATION) {
info->system_table = &systab;
info->parent_handle = parent_image;
} else {
@ -2885,10 +2885,16 @@ efi_status_t EFIAPI efi_start_image(efi_handle_t image_handle,
EFI_ENTRY("%p, %p, %p", image_handle, exit_data_size, exit_data);
if (!efi_search_obj(image_handle))
return EFI_EXIT(EFI_INVALID_PARAMETER);
/* Check parameters */
if (image_obj->header.type != EFI_OBJECT_TYPE_LOADED_IMAGE)
return EFI_EXIT(EFI_INVALID_PARAMETER);
if (image_obj->auth_status != EFI_IMAGE_AUTH_PASSED)
return EFI_EXIT(EFI_SECURITY_VIOLATION);
ret = EFI_CALL(efi_open_protocol(image_handle, &efi_guid_loaded_image,
&info, NULL, NULL,
EFI_OPEN_PROTOCOL_GET_PROTOCOL));

View file

@ -10,7 +10,10 @@
#include <common.h>
#include <cpu_func.h>
#include <efi_loader.h>
#include <malloc.h>
#include <pe.h>
#include <sort.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;
@ -206,6 +209,386 @@ static void efi_set_code_and_data_type(
}
}
#ifdef CONFIG_EFI_SECURE_BOOT
/**
* cmp_pe_section - compare two sections
* @arg1: Pointer to pointer to first section
* @arg2: Pointer to pointer to second section
*
* Compare two sections in PE image.
*
* Return: -1, 0, 1 respectively if arg1 < arg2, arg1 == arg2 or
* arg1 > arg2
*/
static int cmp_pe_section(const void *arg1, const void *arg2)
{
const IMAGE_SECTION_HEADER *section1, *section2;
section1 = *((const IMAGE_SECTION_HEADER **)arg1);
section2 = *((const IMAGE_SECTION_HEADER **)arg2);
if (section1->VirtualAddress < section2->VirtualAddress)
return -1;
else if (section1->VirtualAddress == section2->VirtualAddress)
return 0;
else
return 1;
}
/**
* efi_image_parse - parse a PE image
* @efi: Pointer to image
* @len: Size of @efi
* @regp: 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;
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.
*/
for (i = 0; i < num_sections; i++)
sorted[i] = &sections[i];
qsort(sorted, num_sections, sizeof(sorted[0]), cmp_pe_section);
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
* @efi_size: 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 efi_size)
{
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;
void *new_efi = NULL;
size_t new_efi_size;
bool ret = false;
if (!efi_secure_boot_enabled())
return true;
/*
* 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 false;
memcpy(new_efi, efi, efi_size);
efi = new_efi;
efi_size = new_efi_size;
}
if (!efi_image_parse(efi, efi_size, &regs, &wincerts,
&wincerts_len)) {
debug("Parsing PE executable image failed\n");
goto err;
}
if (!wincerts) {
/* The image is not signed */
ret = efi_image_unsigned_authenticate(regs);
goto err;
}
/*
* 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);
free(new_efi);
return ret;
}
#else
static bool efi_image_authenticate(void *efi, size_t efi_size)
{
return true;
}
#endif /* CONFIG_EFI_SECURE_BOOT */
/**
* efi_load_pe() - relocate EFI binary
*
@ -214,10 +597,12 @@ static void efi_set_code_and_data_type(
*
* @handle: loaded image handle
* @efi: pointer to the EFI binary
* @efi_size: size of @efi binary
* @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;
@ -232,17 +617,41 @@ 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;
efi_status_t ret;
/* 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++)
@ -254,14 +663,29 @@ 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))
handle->auth_status = EFI_IMAGE_AUTH_PASSED;
else
handle->auth_status = EFI_IMAGE_AUTH_FAILED;
/* 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,
@ -280,7 +704,8 @@ 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;
@ -296,7 +721,8 @@ 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;
@ -305,13 +731,16 @@ 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--) {
@ -328,7 +757,8 @@ 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 */
@ -340,5 +770,11 @@ efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, void *efi,
loaded_image_info->image_base = efi_reloc;
loaded_image_info->image_size = virt_size;
return EFI_SUCCESS;
if (handle->auth_status == EFI_IMAGE_AUTH_PASSED)
return EFI_SUCCESS;
else
return EFI_SECURITY_VIOLATION;
err:
return ret;
}