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

[Gerald Elder-Vass <gerald.elder-vass@xxxxxxxxx>]

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. */