efi-boot-shim/MokManager.c

#include <efi.h>
#include <efilib.h>
#include <Library/BaseCryptLib.h>
#include <openssl/x509.h>
#include "shim.h"

#define PASSWORD_LENGTH 16

typedef struct {
	UINT32 MokSize;
	UINT8 *Mok;
} MokListNode;

static EFI_STATUS get_variable (CHAR16 *name, EFI_GUID guid, UINT32 *attributes,
				UINTN *size, void **buffer)
{
	EFI_STATUS efi_status;
	char allocate = !(*size);

	efi_status = uefi_call_wrapper(RT->GetVariable, 5, name, &guid,
				       attributes, size, buffer);

	if (efi_status != EFI_BUFFER_TOO_SMALL || !allocate) {
		return efi_status;
	}

	if (allocate)
		*buffer = AllocatePool(*size);

	if (!*buffer) {
		Print(L"Unable to allocate variable buffer\n");
		return EFI_OUT_OF_RESOURCES;
	}

	efi_status = uefi_call_wrapper(RT->GetVariable, 5, name, &guid,
				       attributes, size, *buffer);

	return efi_status;
}

static EFI_STATUS delete_variable (CHAR16 *name, EFI_GUID guid)
{
	EFI_STATUS efi_status;

	efi_status = uefi_call_wrapper(RT->SetVariable, 5, name, &guid,
				       0, 0, (UINT8 *)NULL);

	return efi_status;
}

static EFI_INPUT_KEY get_keystroke (void)
{
	EFI_INPUT_KEY key;
	UINTN EventIndex;

	uefi_call_wrapper(BS->WaitForEvent, 3, 1, &ST->ConIn->WaitForKey,
			  &EventIndex);
	uefi_call_wrapper(ST->ConIn->ReadKeyStroke, 2, ST->ConIn, &key);

	return key;
}

static EFI_STATUS get_sha256sum (void *Data, int DataSize, UINT8 *hash)
{
	EFI_STATUS status;
	unsigned int ctxsize;
	void *ctx = NULL;

	ctxsize = Sha256GetContextSize();
	ctx = AllocatePool(ctxsize);

	if (!ctx) {
		Print(L"Unable to allocate memory for hash context\n");
		return EFI_OUT_OF_RESOURCES;
	}

	if (!Sha256Init(ctx)) {
		Print(L"Unable to initialise hash\n");
		status = EFI_OUT_OF_RESOURCES;
		goto done;
	}

	if (!(Sha256Update(ctx, Data, DataSize))) {
		Print(L"Unable to generate hash\n");
		status = EFI_OUT_OF_RESOURCES;
		goto done;
	}

	if (!(Sha256Final(ctx, hash))) {
		Print(L"Unable to finalise hash\n");
		status = EFI_OUT_OF_RESOURCES;
		goto done;
	}

	status = EFI_SUCCESS;
done:
	return status;
}

static MokListNode *build_mok_list(UINT32 num, void *Data, UINTN DataSize) {
	MokListNode *list;
	INT64 remain = DataSize;
	int i;
	void *ptr;

	if (DataSize < sizeof(UINT32))
		return NULL;

	list = AllocatePool(sizeof(MokListNode) * num);

	if (!list) {
		Print(L"Unable to allocate MOK list\n");
		return NULL;
	}

	ptr = Data;
	for (i = 0; i < num; i++) {
		CopyMem(&list[i].MokSize, ptr, sizeof(UINT32));
		remain -= sizeof(UINT32) + list[i].MokSize;

		if (remain < 0) {
			Print(L"the list was corrupted\n");
			FreePool(list);
			return NULL;
		}

		ptr += sizeof(UINT32);
		list[i].Mok = ptr;
		ptr += list[i].MokSize;
	}

	return list;
}

static void print_x509_name (X509_NAME *X509Name, CHAR16 *name)
{
	char *str;

	str = X509_NAME_oneline(X509Name, NULL, 0);
	if (str) {
		Print(L"  %s:\n    %a\n", name, str);
		OPENSSL_free(str);
	}
}

static const char *mon[12]= {
"Jan","Feb","Mar","Apr","May","Jun",
"Jul","Aug","Sep","Oct","Nov","Dec"
};

static void print_x509_GENERALIZEDTIME_time (ASN1_TIME *time, CHAR16 *time_string)
{
	char *v;
	int gmt = 0;
	int i;
	int y = 0,M = 0,d = 0,h = 0,m = 0,s = 0;
	char *f = NULL;
	int f_len = 0;

	i=time->length;
	v=(char *)time->data;

	if (i < 12)
		goto error;

	if (v[i-1] == 'Z')
		gmt=1;

	for (i=0; i<12; i++) {
		if ((v[i] > '9') || (v[i] < '0'))
			goto error;
	}

	y = (v[0]-'0')*1000+(v[1]-'0')*100 + (v[2]-'0')*10+(v[3]-'0');
	M = (v[4]-'0')*10+(v[5]-'0');

	if ((M > 12) || (M < 1))
		goto error;

	d = (v[6]-'0')*10+(v[7]-'0');
	h = (v[8]-'0')*10+(v[9]-'0');
	m = (v[10]-'0')*10+(v[11]-'0');

	if (time->length >= 14 &&
	    (v[12] >= '0') && (v[12] <= '9') &&
	    (v[13] >= '0') && (v[13] <= '9')) {
		s = (v[12]-'0')*10+(v[13]-'0');
		/* Check for fractions of seconds. */
		if (time->length >= 15 && v[14] == '.')	{
			int l = time->length;
			f = &v[14];	/* The decimal point. */
			f_len = 1;
			while (14 + f_len < l && f[f_len] >= '0' &&
			       f[f_len] <= '9')
				++f_len;
		}
	}

	SPrint(time_string, 0, L"%a %2d %02d:%02d:%02d%.*a %d%a",
	       mon[M-1], d, h, m, s, f_len, f, y, (gmt)?" GMT":"");
error:
	return;
}

static void print_x509_UTCTIME_time (ASN1_TIME *time, CHAR16 *time_string)
{
	char *v;
	int gmt=0;
	int i;
	int y = 0,M = 0,d = 0,h = 0,m = 0,s = 0;

	i=time->length;
	v=(char *)time->data;

	if (i < 10)
		goto error;

	if (v[i-1] == 'Z')
		gmt=1;

	for (i=0; i<10; i++)
		if ((v[i] > '9') || (v[i] < '0'))
			goto error;

	y = (v[0]-'0')*10+(v[1]-'0');

	if (y < 50)
		y+=100;

	M = (v[2]-'0')*10+(v[3]-'0');

	if ((M > 12) || (M < 1))
		goto error;

	d = (v[4]-'0')*10+(v[5]-'0');
	h = (v[6]-'0')*10+(v[7]-'0');
	m = (v[8]-'0')*10+(v[9]-'0');

	if (time->length >=12 &&
	    (v[10] >= '0') && (v[10] <= '9') &&
	    (v[11] >= '0') && (v[11] <= '9'))
		s = (v[10]-'0')*10+(v[11]-'0');

	SPrint(time_string, 0, L"%a %2d %02d:%02d:%02d %d%a",
	       mon[M-1], d, h, m, s, y+1900, (gmt)?" GMT":"");
error:
	return;
}

static void print_x509_time (ASN1_TIME *time, CHAR16 *name)
{
	CHAR16 time_string[30];

	if (time->type == V_ASN1_UTCTIME) {
		print_x509_UTCTIME_time(time, time_string);
	} else if (time->type == V_ASN1_GENERALIZEDTIME) {
		print_x509_GENERALIZEDTIME_time(time, time_string);
	} else {
		time_string[0] = '\0';
	}

	Print(L"  %s:\n    %s\n", name, time_string);
}

static void show_x509_info (X509 *X509Cert)
{
	ASN1_INTEGER *serial;
	BIGNUM *bnser;
	unsigned char hexbuf[30];
	X509_NAME *X509Name;
	ASN1_TIME *time;

	serial = X509_get_serialNumber(X509Cert);
	if (serial) {
		int i, n;
		bnser = ASN1_INTEGER_to_BN(serial, NULL);
		n = BN_bn2bin(bnser, hexbuf);
		Print(L"  Serial Number:\n    ");
		for (i = 0; i < n-1; i++) {
			Print(L"%02x:", hexbuf[i]);
		}
		Print(L"%02x\n", hexbuf[n-1]);
	}

	X509Name = X509_get_issuer_name(X509Cert);
	if (X509Name) {
		print_x509_name(X509Name, L"Issuer");
	}

	X509Name = X509_get_subject_name(X509Cert);
	if (X509Name) {
		print_x509_name(X509Name, L"Subject");
	}

	time = X509_get_notBefore(X509Cert);
	if (time) {
		print_x509_time(time, L"Validity from");
	}

	time = X509_get_notAfter(X509Cert);
	if (time) {
		print_x509_time(time, L"Validity till");
	}
}

static void show_mok_info (void *Mok, UINTN MokSize)
{
	EFI_STATUS efi_status;
	UINT8 hash[SHA256_DIGEST_SIZE];
	unsigned int i;
	X509 *X509Cert;

	if (!Mok || MokSize == 0)
		return;

	if (X509ConstructCertificate(Mok, MokSize, (UINT8 **) &X509Cert) &&
	    X509Cert != NULL) {
		show_x509_info(X509Cert);
		X509_free(X509Cert);
	} else {
		Print(L"  Not a valid X509 certificate\n\n");
		return;
	}

	efi_status = get_sha256sum(Mok, MokSize, hash);

	if (efi_status != EFI_SUCCESS) {
		Print(L"Failed to compute MOK fingerprint\n");
		return;
	}

	Print(L"  Fingerprint (SHA256):\n    ");
	for (i = 0; i < SHA256_DIGEST_SIZE; i++) {
		Print(L" %02x", hash[i]);
		if (i % 16 == 15)
			Print(L"\n    ");
	}
	Print(L"\n");
}

static INTN get_number ()
{
	EFI_INPUT_KEY input_key;
	CHAR16 input[10];
	int count = 0;

	do {
		input_key = get_keystroke();

		if ((input_key.UnicodeChar < '0' ||
		     input_key.UnicodeChar > '9' ||
		     count >= 10) &&
		    input_key.UnicodeChar != CHAR_BACKSPACE) {
			continue;
		}

		if (count == 0 && input_key.UnicodeChar == CHAR_BACKSPACE)
			continue;

		Print(L"%c", input_key.UnicodeChar);

		if (input_key.UnicodeChar == CHAR_BACKSPACE) {
			input[--count] = '\0';
			continue;
		}

		input[count++] = input_key.UnicodeChar;
	} while (input_key.UnicodeChar != CHAR_CARRIAGE_RETURN);

	if (count == 0)
		return -1;

	input[count] = '\0';

	return (INTN)Atoi(input);
}

static UINT8 list_keys (void *MokNew, UINTN MokNewSize)
{
	UINT32 MokNum;
	MokListNode *keys = NULL;
	INTN key_num = 0;
	UINT8 initial = 1;

	CopyMem(&MokNum, MokNew, sizeof(UINT32));
	if (MokNum == 0) {
		Print(L"No key exists\n");
		return 0;
	}

	keys = build_mok_list(MokNum,
			      (void *)MokNew + sizeof(UINT32),
			      MokNewSize - sizeof(UINT32));

	if (!keys) {
		Print(L"Failed to construct key list in MokNew\n");
		return 0;
	}

	do {
		uefi_call_wrapper(ST->ConOut->ClearScreen, 1, ST->ConOut);
		Print(L"Input the key number to show the details of the key or\n"
		      L"type \'0\' to continue\n\n");
		Print(L"%d key(s) in the new key list\n\n", MokNum);

		if (key_num > MokNum) {
			Print(L"No such key\n\n");
		} else if (initial != 1){
			Print(L"[Key %d]\n", key_num);
			show_mok_info(keys[key_num-1].Mok, keys[key_num-1].MokSize);
		}

		Print(L"Key Number: ");

		key_num = get_number();

		Print(L"\n\n");

		if (key_num == -1)
			continue;

		initial = 0;
	} while (key_num != 0);

	FreePool(keys);

	return 1;
}

static UINT8 mok_enrollment_prompt (void *MokNew, UINTN MokNewSize)
{
	EFI_INPUT_KEY key;

	do {
		if (!list_keys(MokNew, MokNewSize)) {
			return 0;
		}

		Print(L"Enroll the key(s) or list the key(s) again? (y/n/l): ");

		key = get_keystroke();
		Print(L"%c\n", key.UnicodeChar);

		if (key.UnicodeChar == 'Y' || key.UnicodeChar == 'y') {
			return 1;
		}
	} while (key.UnicodeChar == 'L' || key.UnicodeChar == 'l');

	Print(L"Abort\n");

	return 0;
}

static UINT8 mok_deletion_prompt () {
	EFI_INPUT_KEY key;

	Print(L"Erase all stored keys? (y/N): ");

	key = get_keystroke();
	Print(L"%c\n", key.UnicodeChar);

	if (key.UnicodeChar == 'Y' || key.UnicodeChar == 'y') {
		return 1;
	}

	Print(L"Abort\n");

	return 0;
}

static UINT8 get_password (UINT32 *length, CHAR16 *password)
{
	EFI_INPUT_KEY key;
	CHAR16 input[PASSWORD_LENGTH];
	int count = 0;

	do {
		key = get_keystroke();

		if ((count >= PASSWORD_LENGTH &&
		     key.UnicodeChar != CHAR_BACKSPACE) ||
		    key.UnicodeChar == CHAR_NULL ||
		    key.UnicodeChar == CHAR_TAB  ||
		    key.UnicodeChar == CHAR_LINEFEED) {
			continue;
		}

		if (count == 0 && key.UnicodeChar == CHAR_BACKSPACE) {
			continue;
		} else if (key.UnicodeChar == CHAR_BACKSPACE) {
			Print(L"%c", CHAR_BACKSPACE);
			input[--count] = '\0';
			continue;
		}

		input[count++] = key.UnicodeChar;
	} while (key.UnicodeChar != CHAR_CARRIAGE_RETURN);
	Print(L"\n");

	*length = count;
	CopyMem(password, input, count * sizeof(CHAR16));

	return 1;
}

static EFI_STATUS compute_pw_hash (void *MokNew, UINTN MokNewSize, CHAR16 *password,
			     UINT32 pw_length, UINT8 *hash)
{
	EFI_STATUS status;
	unsigned int ctxsize;
	void *ctx = NULL;

	ctxsize = Sha256GetContextSize();
	ctx = AllocatePool(ctxsize);

	if (!ctx) {
		Print(L"Unable to allocate memory for hash context\n");
		return EFI_OUT_OF_RESOURCES;
	}

	if (!Sha256Init(ctx)) {
		Print(L"Unable to initialise hash\n");
		status = EFI_OUT_OF_RESOURCES;
		goto done;
	}

	if (!(Sha256Update(ctx, MokNew, MokNewSize))) {
		Print(L"Unable to generate hash\n");
		status = EFI_OUT_OF_RESOURCES;
		goto done;
	}

	if (!(Sha256Update(ctx, password, pw_length * sizeof(CHAR16)))) {
		Print(L"Unable to generate hash\n");
		status = EFI_OUT_OF_RESOURCES;
		goto done;
	}

	if (!(Sha256Final(ctx, hash))) {
		Print(L"Unable to finalise hash\n");
		status = EFI_OUT_OF_RESOURCES;
		goto done;
	}

	status = EFI_SUCCESS;
done:
	return status;
}

static UINT8 compare_hash (UINT8 *hash1, UINT8 *hash2, UINT32 size)
{
	int i;

	for (i = 0; i < size; i++) {
		if (hash1[i] != hash2[i]) {
			return 0;
		}
	}

	return 1;
}

static EFI_STATUS store_keys (void *MokNew, UINTN MokNewSize)
{
	EFI_GUID shim_lock_guid = SHIM_LOCK_GUID;
	EFI_STATUS efi_status;
	UINT8 hash[SHA256_DIGEST_SIZE];
	UINT8 auth[SHA256_DIGEST_SIZE];
	UINTN auth_size;
	UINT32 attributes;
	CHAR16 password[PASSWORD_LENGTH];
	UINT32 pw_length;
	UINT8 fail_count = 0;

	auth_size = SHA256_DIGEST_SIZE;
	efi_status = uefi_call_wrapper(RT->GetVariable, 5, L"MokAuth",
				       &shim_lock_guid,
				       &attributes, &auth_size, auth);


	if (efi_status != EFI_SUCCESS || auth_size != SHA256_DIGEST_SIZE) {
		Print(L"Failed to get MokAuth %d\n", efi_status);
		return efi_status;
	}

	while (fail_count < 3) {
		Print(L"Password: ");
		get_password(&pw_length, password);

		if (pw_length < 8) {
			Print(L"At 8 characters for the password\n");
		}

		efi_status = compute_pw_hash(MokNew, MokNewSize, password,
					     pw_length, hash);

		if (efi_status != EFI_SUCCESS) {
			return efi_status;
		}

		if (!compare_hash(auth, hash, SHA256_DIGEST_SIZE)) {
			fail_count++;
		} else {
			break;
		}
	}

	if (fail_count >= 3)
		return EFI_ACCESS_DENIED;

	/* Write new MOK */
	efi_status = uefi_call_wrapper(RT->SetVariable, 5, L"MokList",
				       &shim_lock_guid,
				       EFI_VARIABLE_NON_VOLATILE
				       | EFI_VARIABLE_BOOTSERVICE_ACCESS,
				       MokNewSize, MokNew);
	if (efi_status != EFI_SUCCESS) {
		Print(L"Failed to set variable %d\n", efi_status);
		return efi_status;
	}

	return EFI_SUCCESS;
}

static EFI_STATUS check_mok_request(EFI_HANDLE image_handle)
{
	EFI_GUID shim_lock_guid = SHIM_LOCK_GUID;
	EFI_STATUS efi_status;
	UINTN MokNewSize = 0;
	void *MokNew = NULL;
	UINT32 attributes, MokNum;
	UINT8 confirmed;

	efi_status = get_variable(L"MokNew", shim_lock_guid, &attributes,
				  &MokNewSize, &MokNew);

	if (efi_status != EFI_SUCCESS || MokNewSize < sizeof(UINT32)) {
		goto error;
	}

	CopyMem(&MokNum, MokNew, sizeof(UINT32));
	if (MokNum == 0) {
		confirmed = mok_deletion_prompt();

		if (!confirmed)
			goto error;

		efi_status = store_keys(MokNew, sizeof(UINT32));

		if (efi_status != EFI_SUCCESS) {
			Print(L"Failed to erase keys\n");
			goto error;
		}
	} else {
		confirmed = mok_enrollment_prompt(MokNew, MokNewSize);

		if (!confirmed)
			goto error;

		efi_status = store_keys(MokNew, MokNewSize);

		if (efi_status != EFI_SUCCESS) {
			Print(L"Failed to enroll MOK\n");
			goto error;
		}
	}
error:
	if (MokNew) {
		if (delete_variable(L"MokNew", shim_lock_guid) != EFI_SUCCESS) {
			Print(L"Failed to delete MokNew\n");
		}
		FreePool (MokNew);
	}
	delete_variable(L"MokAuth", shim_lock_guid);

	return EFI_SUCCESS;
}

EFI_STATUS efi_main (EFI_HANDLE image_handle, EFI_SYSTEM_TABLE *systab)
{
	EFI_STATUS efi_status;

	InitializeLib(image_handle, systab);

	efi_status = check_mok_request(image_handle);

	return efi_status;
}