[PATCH 2/2] x86/efi: Implement support for embedding SBAT data for x86

Vitaly Kuznetsov
2025-04-24T09:22:27Z

Similar to zboot architectures, implement support for embedding SBAT data
for x86. Put '.sbat' section to the very end of the binary.

Note, the obsolete CRC-32 checksum (see commit 9c54baab4401 ("x86/boot:
Drop CRC-32 checksum and the build tool that generates it")) is gone and
while it would've been possible to reserve the last 4 bytes in '.sbat'
section too (like it's done today in '.data'), it seems to be a pointless
exercise: SBAT makes zero sense without a signature on the EFI binary so
'.sbat' won't be at the very end of the file anyway. Any tool which uses
the last 4 bytes of the file as a checksum is broken with signed EFI
binaries already.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/boot/Makefile | 2 +-
arch/x86/boot/compressed/Makefile | 2 ++
arch/x86/boot/compressed/vmlinux.lds.S | 13 +++++++++++++
arch/x86/boot/header.S | 13 +++++++++++++
drivers/firmware/efi/Kconfig | 2 +-
5 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
index 81f55da81967..5f7b52f0e7f5 100644
--- a/arch/x86/boot/Makefile
+++ b/arch/x86/boot/Makefile
@@ -71,7 +71,7 @@ $(obj)/vmlinux.bin: $(obj)/compressed/vmlinux FORCE

SETUP_OBJS = $(addprefix $(obj)/,$(setup-y))

-sed-zoffset := -e 's/^\([0-9a-fA-F]*\) [a-zA-Z] \(startup_32\|efi.._stub_entry\|efi\(32\)\?_pe_entry\|input_data\|kernel_info\|_end\|_ehead\|_text\|_e\?data\|z_.*\)$$/\#define ZO_\2 0x\1/p'
+sed-zoffset := -e 's/^\([0-9a-fA-F]*\) [a-zA-Z] \(startup_32\|efi.._stub_entry\|efi\(32\)\?_pe_entry\|input_data\|kernel_info\|_end\|_ehead\|_text\|_e\?data\|_e\?sbat\|z_.*\)$$/\#define ZO_\2 0x\1/p'

quiet_cmd_zoffset = ZOFFSET $@
cmd_zoffset = $(NM) $< | sed -n $(sed-zoffset) > $@
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index fdbce022db55..b9b80eccdc02 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -107,6 +107,8 @@ vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/mem.o
vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
vmlinux-libs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a

+vmlinux-objs-$(CONFIG_EFI_SBAT) += $(objtree)/drivers/firmware/efi/libstub/sbat.o
+
$(obj)/vmlinux: $(vmlinux-objs-y) $(vmlinux-libs-y) FORCE
$(call if_changed,ld)

diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index 3b2bc61c9408..d0a27905de90 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -49,9 +49,22 @@ SECTIONS
*(.data.*)

/* Add 4 bytes of extra space for the obsolete CRC-32 checksum */
+#ifndef CONFIG_EFI_SBAT
. = ALIGN(. + 4, 0x200);
+#else
+ /* Avoid gap between '.data' and '.sbat' */
+ . = ALIGN(. + 4, 0x1000);
+#endif
_edata = . ;
}
+#ifdef CONFIG_EFI_SBAT
+ .sbat : ALIGN(0x1000) {
+ _sbat = . ;
+ *(.sbat)
+ _esbat = ALIGN(0x200);
+ . = _esbat;
+ }
+#endif
. = ALIGN(L1_CACHE_BYTES);
.bss : {
_bss = . ;
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index b5c79f43359b..ab851490ef74 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -207,6 +207,19 @@ pecompat_fstart:
IMAGE_SCN_MEM_READ | \
IMAGE_SCN_MEM_WRITE # Characteristics

+#ifdef CONFIG_EFI_SBAT
+ .ascii ".sbat\0\0\0"
+ .long ZO__esbat - ZO__sbat # VirtualSize
+ .long setup_size + ZO__sbat # VirtualAddress
+ .long ZO__esbat - ZO__sbat # SizeOfRawData
+ .long setup_size + ZO__sbat # PointerToRawData
+
+ .long 0, 0, 0
+ .long IMAGE_SCN_CNT_INITIALIZED_DATA | \
+ IMAGE_SCN_MEM_READ | \
+ IMAGE_SCN_MEM_DISCARDABLE # Characteristics
+#endif
+
.set section_count, (. - section_table) / 40
#endif /* CONFIG_EFI_STUB */

diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index 2edb0167ba49..5022a378fec1 100644
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -283,7 +283,7 @@ config EFI_EMBEDDED_FIRMWARE

config EFI_SBAT
bool "Embed SBAT section in the kernel"
- depends on EFI_ZBOOT
+ depends on EFI_ZBOOT || (EFI_STUB && X86)
help
SBAT section provides a way to improve SecureBoot revocations of UEFI
binaries by introducing a generation-based mechanism. With SBAT, older
--
2.49.0