Re: [XEN PATCH v2] sbat: Add SBAT section to the Xen EFI binary

[Frediano Ziglio <frediano.ziglio@xxxxxxxxx>]

On Thu, May 1, 2025 at 1:23 PM Gerald Elder-Vass
<gerald.elder-vass@xxxxxxxxx> wrote:
>
> SBAT is a revocation scheme for UEFI SecureBoot, and is mandated by Microsoft
> for signing.
>
> The SBAT section provides a way for the binary to declare a generation
> id for its upstream source and any vendor changes applied. A compatible
> loader can then revoke vulnerable binaries by generation, using the
> binary's declared generation id(s) to determine if it is safe to load.
>
> More information about SBAT is available here:
> https://github.com/rhboot/shim/blob/main/SBAT.md
>
> Vendors should append a custom line onto sbat.csv(.in) with their vendor
> specific sbat data.
>
> Populate the SBAT section in the Xen binary by using the information
> in xen/arch/x86/sbat.csv
>
> Signed-off-by: Gerald Elder-Vass <gerald.elder-vass@xxxxxxxxx>
> Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
> Tested-by: Gerald Elder-Vass <gerald.elder-vass@xxxxxxxxx>
> ---
> Changed since v1:
>  * Updated commit message to explain why SBAT is needed
>  * Renamed sbat_data.o rule to sbat.o
>  * Moved sbat.o rule into alphabetical order
>  * Removed xen specific entry from sbat.csv (and rule for auto filling 
> version)
>    - The alternative of adding a "customise me" line would result in more
>      overhead for anyone else building Xen, regardless of UEFI SecureBoot 
> usage
>
> diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
> index d902fb7accd9..8fc5c69111d5 100644
> --- a/xen/arch/x86/Makefile
> +++ b/xen/arch/x86/Makefile
> @@ -58,6 +58,7 @@ obj-y += percpu.o
>  obj-y += physdev.o
>  obj-$(CONFIG_COMPAT) += x86_64/physdev.o
>  obj-y += psr.o
> +obj-y += sbat.o
>  obj-y += setup.o
>  obj-y += shutdown.o
>  obj-y += smp.o
> @@ -277,6 +278,9 @@ $(obj)/efi.lds: AFLAGS-y += -DEFI
>  $(obj)/xen.lds $(obj)/efi.lds: $(src)/xen.lds.S FORCE
>         $(call if_changed_dep,cpp_lds_S)
>
> +$(obj)/sbat.o: $(src)/sbat.csv
> +       $(OBJCOPY) -I binary -O elf64-x86-64 --rename-section 
> .data=.sbat,readonly,data,contents $< $@
> +
>  clean-files := \
>      include/asm/asm-macros.* \
>      $(objtree)/.xen-syms.[0-9]* \
> diff --git a/xen/arch/x86/sbat.csv b/xen/arch/x86/sbat.csv
> new file mode 100644
> index 000000000000..1f262b5f038b
> --- /dev/null
> +++ b/xen/arch/x86/sbat.csv
> @@ -0,0 +1 @@
> +sbat,1,SBAT Version,sbat,1,https://github.com/rhboot/shim/blob/main/SBAT.md
> diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
> index 9a1dfe1b340a..e6405941e1b7 100644
> --- a/xen/arch/x86/xen.lds.S
> +++ b/xen/arch/x86/xen.lds.S
> @@ -343,6 +343,8 @@ SECTIONS
>      *(.reloc)
>      __base_relocs_end = .;
>    }
> +
> +  .sbat (NOLOAD) : { *(.sbat) }
>  #elif defined(XEN_BUILD_EFI)
>    /*
>     * Due to the way EFI support is currently implemented, these two symbols
> diff --git a/xen/include/xen/xen.lds.h b/xen/include/xen/xen.lds.h
> index a17810bb286f..756f97d48183 100644
> --- a/xen/include/xen/xen.lds.h
> +++ b/xen/include/xen/xen.lds.h
> @@ -92,7 +92,8 @@
>         *(.comment.*) \
>         *(.note.*)
>  #else
> -#define DISCARD_EFI_SECTIONS
> +#define DISCARD_EFI_SECTIONS \
> +       *(.sbat)
>  #endif
>
>  /* Sections to be discarded. */

Reviewed-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>

Frediano