[PATCH] efi: zboot: Ensure zboot PIC

[Pingfan Liu <kernelfans@gmail.com>]

Using objcopy to reform vmlinuz.efi.elf to vmlinuz.efi will not convey
any relocation information. That means vmlinuz.efi is expected to be
PIC.

At present, vmlinuz.efi is PIC. But it is better to adopt the same
solution used by the kernel to resolve the code relocation issue by
itself. That is to resolve R_AARCH64_RELATIVE at the runtime.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
To: linux-efi@vger.kernel.org
---
 drivers/firmware/efi/libstub/Makefile       |  2 +-
 drivers/firmware/efi/libstub/Makefile.zboot |  2 +-
 drivers/firmware/efi/libstub/zboot-entry.S  | 35 +++++++++++++++++++++
 drivers/firmware/efi/libstub/zboot.c        |  2 +-
 drivers/firmware/efi/libstub/zboot.lds      |  6 ++++
 5 files changed, 44 insertions(+), 3 deletions(-)
 create mode 100644 drivers/firmware/efi/libstub/zboot-entry.S

diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index 80d85a5169fb..4447395d7218 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -95,7 +95,7 @@ lib-$(CONFIG_LOONGARCH)		+= loongarch.o loongarch-stub.o
 CFLAGS_arm32-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
 
 zboot-obj-$(CONFIG_RISCV)	:= lib-clz_ctz.o lib-ashldi3.o
-lib-$(CONFIG_EFI_ZBOOT)		+= zboot.o $(zboot-obj-y)
+lib-$(CONFIG_EFI_ZBOOT)		+= zboot-entry.o zboot.o $(zboot-obj-y)
 
 extra-y				:= $(lib-y)
 lib-y				:= $(patsubst %.o,%.stub.o,$(lib-y))
diff --git a/drivers/firmware/efi/libstub/Makefile.zboot b/drivers/firmware/efi/libstub/Makefile.zboot
index 43e9a4cab9f5..1ed948cee92f 100644
--- a/drivers/firmware/efi/libstub/Makefile.zboot
+++ b/drivers/firmware/efi/libstub/Makefile.zboot
@@ -36,7 +36,7 @@ $(obj)/zboot-header.o: $(srctree)/drivers/firmware/efi/libstub/zboot-header.S FO
 
 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
+LDFLAGS_vmlinuz.efi.elf :=  --no-undefined -X -shared -Bsymbolic -z notext --no-apply-dynamic-relocs -T $(srctree)/drivers/firmware/efi/libstub/zboot.lds
 $(obj)/vmlinuz.efi.elf: $(obj)/vmlinuz.o $(ZBOOT_DEPS) FORCE
 	$(call if_changed,ld)
 
diff --git a/drivers/firmware/efi/libstub/zboot-entry.S b/drivers/firmware/efi/libstub/zboot-entry.S
new file mode 100644
index 000000000000..072207f2f6ba
--- /dev/null
+++ b/drivers/firmware/efi/libstub/zboot-entry.S
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <asm/elf.h>
+#define ZBOOT_HEADER_BASE 0
+
+	.text
+/*
+ * x0: efi_handle_t
+ * x1: efi_system_table_t *
+ */
+	.global efi_zboot_entry
+efi_zboot_entry:
+	adrp	x2, efi_zboot_header
+	add	x2, x2, :lo12:efi_zboot_header
+	mov	x3, ZBOOT_HEADER_BASE
+	sub	x3, x2, x3		// delta between actual and linked address
+	adrp	x4, _rela_start
+	add	x4, x4, :lo12:_rela_start
+	adrp	x5, _rela_end
+	add	x5, x5, :lo12:_rela_end
+
+0:	cmp	x5, x4
+	b.hs	1f
+	ldp	x6, x7, [x4], #24
+	ldr	x8, [x4, #-8]
+	cmp	w7, #R_AARCH64_RELATIVE
+	b.ne	0b
+	add	x8, x8, x3
+	str	x8, [x6, x3]
+	b	0b
+
+1:
+	dsb	ishst
+	ic	iallu
+	b	efi_zboot_main
diff --git a/drivers/firmware/efi/libstub/zboot.c b/drivers/firmware/efi/libstub/zboot.c
index ba234e062a1a..7aa6b2e6d104 100644
--- a/drivers/firmware/efi/libstub/zboot.c
+++ b/drivers/firmware/efi/libstub/zboot.c
@@ -58,7 +58,7 @@ void __weak efi_cache_sync_image(unsigned long image_base,
 }
 
 asmlinkage efi_status_t __efiapi
-efi_zboot_entry(efi_handle_t handle, efi_system_table_t *systab)
+efi_zboot_main(efi_handle_t handle, efi_system_table_t *systab)
 {
 	unsigned long compressed_size = _gzdata_end - _gzdata_start;
 	unsigned long image_base, alloc_size, code_size;
diff --git a/drivers/firmware/efi/libstub/zboot.lds b/drivers/firmware/efi/libstub/zboot.lds
index 93d33f68333b..631942604c3f 100644
--- a/drivers/firmware/efi/libstub/zboot.lds
+++ b/drivers/firmware/efi/libstub/zboot.lds
@@ -12,6 +12,12 @@ SECTIONS
 		*(.text* .init.text*)
 	}
 
+	.rela.dyn : ALIGN(8) {
+		__efistub__rela_start = .;
+		*(.rela .rela*)
+		__efistub__rela_end = .;
+	}
+
 	.rodata : ALIGN(8) {
 		__efistub__gzdata_start = .;
 		*(.gzdata)
-- 
2.31.1