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Add build options to fully disable fallback and mok mechanism. #731

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Add build options to fully disable fallback and mok mechanism. #731

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c2946f3
Add an option to disable fallback image
zeetim Mar 7, 2025
a7bc196
Add an option to disable mok support
zeetim Mar 7, 2025
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21 changes: 16 additions & 5 deletions Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -25,22 +25,33 @@ include $(TOPDIR)/include/scan-build.mk
include $(TOPDIR)/include/fanalyzer.mk

TARGETS = $(SHIMNAME)
TARGETS += $(SHIMNAME).debug $(MMNAME).debug $(FBNAME).debug
TARGETS += $(SHIMNAME).debug $(if $(DISABLE_MOK),,$(MMNAME).debug) $(if $(DISABLE_FALLBACK),,$(FBNAME).debug)
ifneq ($(origin ENABLE_SHIM_HASH),undefined)
TARGETS += $(SHIMHASHNAME)
endif
ifneq ($(origin ENABLE_SHIM_DEVEL),undefined)
CFLAGS += -DENABLE_SHIM_DEVEL
endif
ifneq ($(origin ENABLE_SHIM_CERT),undefined)
TARGETS += $(MMNAME).signed $(FBNAME).signed
TARGETS += $(if $(DISABLE_MOK),,$(MMNAME).signed) $(if $(DISABLE_FALLBACK),,$(FBNAME).signed)
CFLAGS += -DENABLE_SHIM_CERT
else
TARGETS += $(MMNAME) $(FBNAME)
TARGETS += $(if $(DISABLE_MOK),,$(MMNAME)) $(if $(DISABLE_FALLBACK),,$(FBNAME))
endif
OBJS = shim.o globals.o memattrs.o mok.o netboot.o cert.o dp.o loader-proto.o tpm.o version.o errlog.o sbat.o sbat_data.o sbat_var.o pe.o pe-relocate.o httpboot.o csv.o load-options.o utils.o

ifneq ($(origin DISABLE_FALLBACK),undefined)
$(warning Building shim without fallback image support)
CFLAGS += -DDISABLE_FALLBACK
endif

ifneq ($(origin DISABLE_MOK),undefined)
$(warning Building shim without mok support)
CFLAGS += -DDISABLE_MOK
endif

OBJS = shim.o globals.o memattrs.o $(if $(DISABLE_MOK),,mok.o) netboot.o cert.o dp.o loader-proto.o tpm.o version.o errlog.o sbat.o sbat_data.o sbat_var.o pe.o pe-relocate.o httpboot.o csv.o load-options.o utils.o
KEYS = shim_cert.h ocsp.* ca.* shim.crt shim.csr shim.p12 shim.pem shim.key shim.cer
ORIG_SOURCES = shim.c globals.c memattrs.c mok.c netboot.c dp.c loader-proto.c tpm.c errlog.c sbat.c pe.c pe-relocate.c httpboot.c shim.h version.h $(wildcard include/*.h) cert.S sbat_var.S
ORIG_SOURCES = shim.c globals.c memattrs.c $(if $(DISABLE_MOK),,mok.c) netboot.c dp.c loader-proto.c tpm.c errlog.c sbat.c pe.c pe-relocate.c httpboot.c shim.h version.h $(wildcard include/*.h) cert.S sbat_var.S
MOK_OBJS = MokManager.o PasswordCrypt.o crypt_blowfish.o errlog.o sbat_data.o globals.o dp.o
ORIG_MOK_SOURCES = MokManager.c PasswordCrypt.c crypt_blowfish.c shim.h $(wildcard include/*.h)
FALLBACK_OBJS = fallback.o tpm.o errlog.o sbat_data.o globals.o utils.o
Expand Down
20 changes: 16 additions & 4 deletions shim.c
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Original file line number Diff line number Diff line change
Expand Up @@ -316,6 +316,7 @@ static EFI_STATUS check_denylist (WIN_CERTIFICATE_EFI_PKCS *cert,
LogError(L"cert sha256hash found in system dbx\n");
return EFI_SECURITY_VIOLATION;
}
#ifndef DISABLE_MOK
if (check_db_hash(L"MokListX", SHIM_LOCK_GUID, sha256hash,
SHA256_DIGEST_SIZE, EFI_CERT_SHA256_GUID) == DATA_FOUND) {
LogError(L"binary sha256hash found in Mok dbx\n");
Expand All @@ -327,7 +328,7 @@ static EFI_STATUS check_denylist (WIN_CERTIFICATE_EFI_PKCS *cert,
LogError(L"cert sha256hash found in Mok dbx\n");
return EFI_SECURITY_VIOLATION;
}

#endif
drain_openssl_errors();
return EFI_SUCCESS;
}
Expand Down Expand Up @@ -394,7 +395,7 @@ static EFI_STATUS check_allowlist (WIN_CERTIFICATE_EFI_PKCS *cert,
LogError(L"check_db_cert(vendor_db, sha256hash) != DATA_FOUND\n");
}
#endif

#ifndef DISABLE_MOK
if (check_db_hash(L"MokListRT", SHIM_LOCK_GUID, sha256hash,
SHA256_DIGEST_SIZE, EFI_CERT_SHA256_GUID)
== DATA_FOUND) {
Expand All @@ -412,7 +413,7 @@ static EFI_STATUS check_allowlist (WIN_CERTIFICATE_EFI_PKCS *cert,
} else if (cert) {
LogError(L"check_db_cert(MokListRT, sha256hash) != DATA_FOUND\n");
}

#endif
update_verification_method(VERIFIED_BY_NOTHING);
return EFI_NOT_FOUND;
}
Expand Down Expand Up @@ -778,6 +779,7 @@ verify_buffer (char *data, int datasize,
return verify_buffer_sbat(data, datasize, context);
}

#ifndef DISABLE_FALLBACK
static int
should_use_fallback(EFI_HANDLE image_handle)
{
Expand Down Expand Up @@ -834,6 +836,7 @@ should_use_fallback(EFI_HANDLE image_handle)

return ret;
}
#endif
/*
* Open the second stage bootloader and read it into a buffer
*/
Expand Down Expand Up @@ -1210,9 +1213,14 @@ EFI_STATUS start_image(EFI_HANDLE image_handle, CHAR16 *ImagePath)
EFI_STATUS init_grub(EFI_HANDLE image_handle)
{
EFI_STATUS efi_status;
#ifndef DISABLE_FALLBACK
int use_fb = should_use_fallback(image_handle);
#else
int use_fb = 0;
#endif

efi_status = start_image(image_handle, use_fb ? FALLBACK :second_stage);
#ifndef DISABLE_MOK
if (efi_status == EFI_SECURITY_VIOLATION ||
efi_status == EFI_ACCESS_DENIED) {
efi_status = start_image(image_handle, MOK_MANAGER);
Expand All @@ -1225,7 +1233,7 @@ EFI_STATUS init_grub(EFI_HANDLE image_handle)
efi_status = start_image(image_handle,
use_fb ? FALLBACK : second_stage);
}

#endif
/*
* If the filename is invalid, or the file does not exist, just fall
* back to the default loader. Also fall back to the default loader
Expand Down Expand Up @@ -2048,7 +2056,11 @@ efi_main (EFI_HANDLE passed_image_handle, EFI_SYSTEM_TABLE *passed_systab)
* Before we do anything else, validate our non-volatile,
* boot-services-only state variables are what we think they are.
*/
#ifndef DISABLE_MOK
efi_status = import_mok_state(image_handle);
#else
efi_status = EFI_SUCCESS;
#endif
if (!secure_mode() &&
(efi_status == EFI_INVALID_PARAMETER ||
efi_status == EFI_OUT_OF_RESOURCES)) {
Expand Down