| Message ID | 20250505154523.231233-2-vkuznets@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | efi: Add a mechanism for embedding SBAT section | expand |
On Mon, 5 May 2025 at 17:45, Vitaly Kuznetsov <vkuznets@redhat.com> wrote: > > SBAT is a mechanism which improves SecureBoot revocations of UEFI binaries > by introducing a generation-based technique. Compromised or vulnerable UEFI > binaries can be prevented from booting by bumping the minimal required > generation for the specific component in the bootloader. More information > on the SBAT can be obtained here: > > https://github.com/rhboot/shim/blob/main/SBAT.md > > Upstream Linux kernel does not currently participate in any way in SBAT as > there's no existing policy in how SBAT generation number should be > defined. Keep the status quo and provide a mechanism for distro vendors and > anyone else who signs their kernel for SecureBoot to include their own SBAT > data. This leaves the decision on the policy to the vendor. Basically, each > distro implementing SecureBoot today, will have an option to inject their > own SBAT data during kernel build and before it gets signed by their > SecureBoot CA. Different distro do not need to agree on the common SBAT > component names or generation numbers as each distro ships its own 'shim' > with their own 'vendor_cert'/'vendor_db' > > Implement support for embedding SBAT data for architectures using > zboot (arm64, loongarch, riscv). Put '.sbat' section in between '.data' and > '.text' as the former also covers '.bss' and thus must be the last one. > > Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Reviewed-by: Ard Biesheuvel <ardb@kernel.org> > --- > drivers/firmware/efi/Kconfig | 24 +++++++++++++++++++++ > drivers/firmware/efi/libstub/Makefile.zboot | 4 ++++ > drivers/firmware/efi/libstub/zboot-header.S | 22 +++++++++++++++++-- > drivers/firmware/efi/libstub/zboot.lds | 11 ++++++++++ > 4 files changed, 59 insertions(+), 2 deletions(-) > > diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig > index 5fe61b9ab5f9..db8c5c03d3a2 100644 > --- a/drivers/firmware/efi/Kconfig > +++ b/drivers/firmware/efi/Kconfig > @@ -281,6 +281,30 @@ config EFI_EMBEDDED_FIRMWARE > bool > select CRYPTO_LIB_SHA256 > > +config EFI_SBAT > + def_bool y if EFI_SBAT_FILE!="" > + > +config EFI_SBAT_FILE > + string "Embedded SBAT section file path" > + depends on EFI_ZBOOT > + help > + SBAT section provides a way to improve SecureBoot revocations of UEFI > + binaries by introducing a generation-based mechanism. With SBAT, older > + UEFI binaries can be prevented from booting by bumping the minimal > + required generation for the specific component in the bootloader. > + > + Note: SBAT information is distribution specific, i.e. the owner of the > + signing SecureBoot certificate must define the SBAT policy. Linux > + kernel upstream does not define SBAT components and their generations. > + > + See https://github.com/rhboot/shim/blob/main/SBAT.md for the additional > + details. > + > + Specify a file with SBAT data which is going to be embedded as '.sbat' > + section into the kernel. > + > + If unsure, leave blank. > + > endmenu > > config UEFI_CPER > diff --git a/drivers/firmware/efi/libstub/Makefile.zboot b/drivers/firmware/efi/libstub/Makefile.zboot > index 48842b5c106b..92e3c73502ba 100644 > --- a/drivers/firmware/efi/libstub/Makefile.zboot > +++ b/drivers/firmware/efi/libstub/Makefile.zboot > @@ -44,6 +44,10 @@ AFLAGS_zboot-header.o += -DMACHINE_TYPE=IMAGE_FILE_MACHINE_$(EFI_ZBOOT_MACH_TYPE > $(obj)/zboot-header.o: $(srctree)/drivers/firmware/efi/libstub/zboot-header.S FORCE > $(call if_changed_rule,as_o_S) > > +ifneq ($(CONFIG_EFI_SBAT_FILE),) > +$(obj)/zboot-header.o: $(CONFIG_EFI_SBAT_FILE) > +endif > + > ZBOOT_DEPS := $(obj)/zboot-header.o $(objtree)/drivers/firmware/efi/libstub/lib.a > > LDFLAGS_vmlinuz.efi.elf := -T $(srctree)/drivers/firmware/efi/libstub/zboot.lds > diff --git a/drivers/firmware/efi/libstub/zboot-header.S b/drivers/firmware/efi/libstub/zboot-header.S > index fb676ded47fa..e02247458b65 100644 > --- a/drivers/firmware/efi/libstub/zboot-header.S > +++ b/drivers/firmware/efi/libstub/zboot-header.S > @@ -123,11 +123,29 @@ __efistub_efi_zboot_header: > IMAGE_SCN_MEM_READ | \ > IMAGE_SCN_MEM_EXECUTE > > +#ifdef CONFIG_EFI_SBAT > + .ascii ".sbat\0\0\0" > + .long __sbat_size > + .long _sbat - .Ldoshdr > + .long __sbat_size > + .long _sbat - .Ldoshdr > + > + .long 0, 0 > + .short 0, 0 > + .long IMAGE_SCN_CNT_INITIALIZED_DATA | \ > + IMAGE_SCN_MEM_READ | \ > + IMAGE_SCN_MEM_DISCARDABLE > + > + .pushsection ".sbat", "a", @progbits > + .incbin CONFIG_EFI_SBAT_FILE > + .popsection > +#endif > + > .ascii ".data\0\0\0" > .long __data_size > - .long _etext - .Ldoshdr > + .long _data - .Ldoshdr > .long __data_rawsize > - .long _etext - .Ldoshdr > + .long _data - .Ldoshdr > > .long 0, 0 > .short 0, 0 > diff --git a/drivers/firmware/efi/libstub/zboot.lds b/drivers/firmware/efi/libstub/zboot.lds > index 9ecc57ff5b45..c3a166675450 100644 > --- a/drivers/firmware/efi/libstub/zboot.lds > +++ b/drivers/firmware/efi/libstub/zboot.lds > @@ -29,7 +29,17 @@ SECTIONS > . = _etext; > } > > +#ifdef CONFIG_EFI_SBAT > + .sbat : ALIGN(4096) { > + _sbat = .; > + *(.sbat) > + _esbat = ALIGN(4096); > + . = _esbat; > + } > +#endif > + > .data : ALIGN(4096) { > + _data = .; > *(.data* .init.data*) > _edata = ALIGN(512); > . = _edata; > @@ -52,3 +62,4 @@ PROVIDE(__efistub__gzdata_size = > > PROVIDE(__data_rawsize = ABSOLUTE(_edata - _etext)); > PROVIDE(__data_size = ABSOLUTE(_end - _etext)); > +PROVIDE(__sbat_size = ABSOLUTE(_esbat - _sbat)); > -- > 2.49.0 >
diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig index 5fe61b9ab5f9..db8c5c03d3a2 100644 --- a/drivers/firmware/efi/Kconfig +++ b/drivers/firmware/efi/Kconfig @@ -281,6 +281,30 @@ config EFI_EMBEDDED_FIRMWARE bool select CRYPTO_LIB_SHA256 +config EFI_SBAT + def_bool y if EFI_SBAT_FILE!="" + +config EFI_SBAT_FILE + string "Embedded SBAT section file path" + depends on EFI_ZBOOT + help + SBAT section provides a way to improve SecureBoot revocations of UEFI + binaries by introducing a generation-based mechanism. With SBAT, older + UEFI binaries can be prevented from booting by bumping the minimal + required generation for the specific component in the bootloader. + + Note: SBAT information is distribution specific, i.e. the owner of the + signing SecureBoot certificate must define the SBAT policy. Linux + kernel upstream does not define SBAT components and their generations. + + See https://github.com/rhboot/shim/blob/main/SBAT.md for the additional + details. + + Specify a file with SBAT data which is going to be embedded as '.sbat' + section into the kernel. + + If unsure, leave blank. + endmenu config UEFI_CPER diff --git a/drivers/firmware/efi/libstub/Makefile.zboot b/drivers/firmware/efi/libstub/Makefile.zboot index 48842b5c106b..92e3c73502ba 100644 --- a/drivers/firmware/efi/libstub/Makefile.zboot +++ b/drivers/firmware/efi/libstub/Makefile.zboot @@ -44,6 +44,10 @@ AFLAGS_zboot-header.o += -DMACHINE_TYPE=IMAGE_FILE_MACHINE_$(EFI_ZBOOT_MACH_TYPE $(obj)/zboot-header.o: $(srctree)/drivers/firmware/efi/libstub/zboot-header.S FORCE $(call if_changed_rule,as_o_S) +ifneq ($(CONFIG_EFI_SBAT_FILE),) +$(obj)/zboot-header.o: $(CONFIG_EFI_SBAT_FILE) +endif + ZBOOT_DEPS := $(obj)/zboot-header.o $(objtree)/drivers/firmware/efi/libstub/lib.a LDFLAGS_vmlinuz.efi.elf := -T $(srctree)/drivers/firmware/efi/libstub/zboot.lds diff --git a/drivers/firmware/efi/libstub/zboot-header.S b/drivers/firmware/efi/libstub/zboot-header.S index fb676ded47fa..e02247458b65 100644 --- a/drivers/firmware/efi/libstub/zboot-header.S +++ b/drivers/firmware/efi/libstub/zboot-header.S @@ -123,11 +123,29 @@ __efistub_efi_zboot_header: IMAGE_SCN_MEM_READ | \ IMAGE_SCN_MEM_EXECUTE +#ifdef CONFIG_EFI_SBAT + .ascii ".sbat\0\0\0" + .long __sbat_size + .long _sbat - .Ldoshdr + .long __sbat_size + .long _sbat - .Ldoshdr + + .long 0, 0 + .short 0, 0 + .long IMAGE_SCN_CNT_INITIALIZED_DATA | \ + IMAGE_SCN_MEM_READ | \ + IMAGE_SCN_MEM_DISCARDABLE + + .pushsection ".sbat", "a", @progbits + .incbin CONFIG_EFI_SBAT_FILE + .popsection +#endif + .ascii ".data\0\0\0" .long __data_size - .long _etext - .Ldoshdr + .long _data - .Ldoshdr .long __data_rawsize - .long _etext - .Ldoshdr + .long _data - .Ldoshdr .long 0, 0 .short 0, 0 diff --git a/drivers/firmware/efi/libstub/zboot.lds b/drivers/firmware/efi/libstub/zboot.lds index 9ecc57ff5b45..c3a166675450 100644 --- a/drivers/firmware/efi/libstub/zboot.lds +++ b/drivers/firmware/efi/libstub/zboot.lds @@ -29,7 +29,17 @@ SECTIONS . = _etext; } +#ifdef CONFIG_EFI_SBAT + .sbat : ALIGN(4096) { + _sbat = .; + *(.sbat) + _esbat = ALIGN(4096); + . = _esbat; + } +#endif + .data : ALIGN(4096) { + _data = .; *(.data* .init.data*) _edata = ALIGN(512); . = _edata; @@ -52,3 +62,4 @@ PROVIDE(__efistub__gzdata_size = PROVIDE(__data_rawsize = ABSOLUTE(_edata - _etext)); PROVIDE(__data_size = ABSOLUTE(_end - _etext)); +PROVIDE(__sbat_size = ABSOLUTE(_esbat - _sbat));
SBAT is a mechanism which improves SecureBoot revocations of UEFI binaries by introducing a generation-based technique. Compromised or vulnerable UEFI binaries can be prevented from booting by bumping the minimal required generation for the specific component in the bootloader. More information on the SBAT can be obtained here: https://github.com/rhboot/shim/blob/main/SBAT.md Upstream Linux kernel does not currently participate in any way in SBAT as there's no existing policy in how SBAT generation number should be defined. Keep the status quo and provide a mechanism for distro vendors and anyone else who signs their kernel for SecureBoot to include their own SBAT data. This leaves the decision on the policy to the vendor. Basically, each distro implementing SecureBoot today, will have an option to inject their own SBAT data during kernel build and before it gets signed by their SecureBoot CA. Different distro do not need to agree on the common SBAT component names or generation numbers as each distro ships its own 'shim' with their own 'vendor_cert'/'vendor_db' Implement support for embedding SBAT data for architectures using zboot (arm64, loongarch, riscv). Put '.sbat' section in between '.data' and '.text' as the former also covers '.bss' and thus must be the last one. Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> --- drivers/firmware/efi/Kconfig | 24 +++++++++++++++++++++ drivers/firmware/efi/libstub/Makefile.zboot | 4 ++++ drivers/firmware/efi/libstub/zboot-header.S | 22 +++++++++++++++++-- drivers/firmware/efi/libstub/zboot.lds | 11 ++++++++++ 4 files changed, 59 insertions(+), 2 deletions(-)