ARM: kernel: make vmlinux buildable as a PIE executable

maillist inclusion
commit 04be01192973461cdd00ab47908a78f0e2f55ef8
category: feature
feature: ARM kaslr support
bugzilla: 47952
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/commit/?h=arm-kaslr-latest&id=04be01192973461cdd00ab47908a78f0e2f55ef8

Update the Kconfig RELOCATABLE depends on !JUMP_LABEL to resolve
compilation conflicts between fpic and JUMP_LABEL

-------------------------------------------------

Update the build flags and linker script to allow vmlinux to be built
as a PIE  binary, which retains relocation information about absolute
symbol references so that they can be fixed up at runtime. This will
be used for implementing KASLR,

Cc: Russell King <linux@armlinux.org.uk>
Acked-by: NNicolas Pitre <nico@linaro.org>
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NCui GaoSheng <cuigaosheng1@huawei.com>
Reviewed-by: NXiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/arm/Kconfig

@@ -1678,6 +1678,11 @@ config STACKPROTECTOR_PER_TASK
 	  Enable this option to switch to a different method that uses a
 	  different canary value for each task.
 
+config RELOCATABLE
+	bool
+	depends on !XIP_KERNEL && !JUMP_LABEL
+	select HAVE_ARCH_PREL32_RELOCATIONS
+
 endmenu
 
 menu "Boot options"

arch/arm/Makefile

@@ -48,6 +48,11 @@ CHECKFLAGS	+= -D__ARMEL__
 KBUILD_LDFLAGS	+= -EL
 endif
 
+ifeq ($(CONFIG_RELOCATABLE),y)
+KBUILD_CFLAGS		+= -fpic -include $(srctree)/include/linux/hidden.h
+LDFLAGS_vmlinux		+= -pie -shared -Bsymbolic
+endif
+
 #
 # The Scalar Replacement of Aggregates (SRA) optimization pass in GCC 4.9 and
 # later may result in code being generated that handles signed short and signed

arch/arm/include/asm/assembler.h

@@ -528,7 +528,7 @@ THUMB(	orr	\reg , \reg , #PSR_T_BIT	)
 	 * mov_l - move a constant value or [relocated] address into a register
 	 */
 	.macro		mov_l, dst:req, imm:req
-	.if		__LINUX_ARM_ARCH__ < 7
+	.if		CONFIG_RELOCATABLE == 1 || __LINUX_ARM_ARCH__ < 7
 	ldr		\dst, =\imm
 	.else
 	movw		\dst, #:lower16:\imm

arch/arm/include/asm/vmlinux.lds.h

@@ -50,7 +50,11 @@
 		EXIT_CALL						\
 		ARM_MMU_DISCARD(*(.text.fixup))				\
 		ARM_MMU_DISCARD(*(__ex_table))				\
-		COMMON_DISCARDS
+		COMMON_DISCARDS						\
+		*(.ARM.exidx.discard.text)				\
+		*(.interp .dynamic)					\
+		*(.dynsym .dynstr .hash)
+
 
 /*
  * Sections that should stay zero sized, which is safer to explicitly

arch/arm/kernel/vmlinux.lds.S

@@ -115,6 +115,12 @@ SECTIONS
 		__smpalt_end = .;
 	}
 #endif
+	.rel.dyn : ALIGN(8) {
+		__rel_begin = .;
+		*(.rel .rel.* .rel.dyn)
+	}
+	__rel_end = ADDR(.rel.dyn) + SIZEOF(.rel.dyn);
+
 	.init.pv_table : {
 		__pv_table_begin = .;
 		*(.pv_table)

scripts/module.lds.S

@@ -7,6 +7,7 @@ SECTIONS {
 	/DISCARD/ : {
 		*(.discard)
 		*(.discard.*)
+		*(*.discard.*)
 	}
 
 	__ksymtab		0 : { *(SORT(___ksymtab+*)) }