As an intermediate step towards enabling PIE linking for the x86_64 KASLR kernel, enable PIE codegen for all C and Rust objects that are linked into the kernel proper. Add a Kconfig option RELOCATABLE_PIE for this, depending on RELR support in the linker, as the relocation tables will blow up the kernel image otherwise.
This results in a code size increase of between 0.2% (clang) and 0.5% (gcc). Performance (hackbench) appears to be unaffected across several different uarchs. Signed-off-by: Ard Biesheuvel <[email protected]> --- arch/x86/Kconfig | 4 ++++ arch/x86/Makefile | 19 ++++++++++++++++++- arch/x86/boot/Makefile | 1 + arch/x86/boot/compressed/Makefile | 2 +- arch/x86/entry/vdso/Makefile | 1 + arch/x86/realmode/rm/Makefile | 1 + include/asm-generic/vmlinux.lds.h | 1 + include/linux/hidden.h | 2 ++ 8 files changed, 29 insertions(+), 2 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index bf51e17d5813..b3a64cfe04cf 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2067,6 +2067,7 @@ config PHYSICAL_START config RELOCATABLE bool "Build a relocatable kernel" if X86_32 default X86_32 + select RELOCATABLE_PIE if TOOLS_SUPPORT_RELR help This builds a kernel image that retains relocation information so it can be placed someplace besides the default PAGE_OFFSET + 1MB. This @@ -2087,6 +2088,9 @@ config RELOCATABLE it has been loaded at and the compile time physical address (CONFIG_PHYSICAL_START) is used as the minimum location. +config RELOCATABLE_PIE + bool + config RANDOMIZE_BASE bool "Randomize the address of the kernel image (KASLR)" select RELOCATABLE diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 1d403a3612ea..b211d6c950aa 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -89,6 +89,8 @@ ifdef CONFIG_CC_IS_GCC CC_FLAGS_FPU += -mhard-float endif +rustflags-nojumptables := $(if $(call rustc-min-version,109300),-Cjump-tables=n,-Zno-jump-tables) + ifeq ($(CONFIG_X86_KERNEL_IBT),y) # # Kernel IBT has S_CET.NOTRACK_EN=0, as such the compilers must not generate @@ -100,7 +102,7 @@ ifeq ($(CONFIG_X86_KERNEL_IBT),y) # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104816 # KBUILD_CFLAGS += $(call cc-option,-fcf-protection=branch -fno-jump-tables) -KBUILD_RUSTFLAGS += -Zcf-protection=branch $(if $(call rustc-min-version,109300),-Cjump-tables=n,-Zno-jump-tables) +KBUILD_RUSTFLAGS += -Zcf-protection=branch $(rustflags-nojumptables) else KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none) endif @@ -178,6 +180,21 @@ endif KBUILD_RUSTFLAGS += -Ccode-model=kernel percpu_seg := gs + + pie-ccflags-$(CONFIG_CC_IS_GCC) += $(call cc-option.-mdirect-extern-access) + pie-ccflags-$(CONFIG_CC_IS_CLANG) += -fdirect-access-external-data + + # objtool gets confused by unannotated PIC flavor jump tables + pie-ccflags-y += $(call cc-option,-fannotate-jump-tables,-fno-jump-tables) + + pie-cflags-$(CONFIG_RELOCATABLE_PIE) := $(pie-ccflags-y) -fpie -mcmodel=small \ + -include $(srctree)/include/linux/hidden.h + pie-rustflags-$(CONFIG_RELOCATABLE_PIE) := -Crelocation-model=pie \ + -Ccode-model=small -Zdirect-access-external-data=yes \ + $(rustflags-nojumptables) + + KBUILD_CFLAGS_KERNEL += $(pie-cflags-y) + KBUILD_RUSTFLAGS_KERNEL += $(pie-rustflags-y) endif ifeq ($(CONFIG_STACKPROTECTOR),y) diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile index 3f9fb3698d66..491b3b2a9a02 100644 --- a/arch/x86/boot/Makefile +++ b/arch/x86/boot/Makefile @@ -55,6 +55,7 @@ KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables KBUILD_CFLAGS += $(CONFIG_CC_IMPLICIT_FALLTHROUGH) +KBUILD_CFLAGS_KERNEL := $(obj)/bzImage: asflags-y := $(SVGA_MODE) diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index bc071bdcd11e..96099b5d1064 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -76,7 +76,7 @@ LDFLAGS_vmlinux += -T hostprogs := mkpiggy HOST_EXTRACFLAGS += -I$(srctree)/tools/include -sed-voffset := -e 's/^\([0-9a-fA-F]*\) [ABbCDGRSTtVW] \(_text\|__data_segment_start\|__bss_start\|_end\)$$/\#define VO_\2 _AC(0x\1,UL)/p' +sed-voffset := -e 's/^\([0-9a-fA-F]*\) [ABbCDdGRSTtVW] \(_text\|__data_segment_start\|__bss_start\|_end\)$$/\#define VO_\2 _AC(0x\1,UL)/p' quiet_cmd_voffset = VOFFSET $@ cmd_voffset = $(NM) $< | sed -n $(sed-voffset) > $@ diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile index f247f5f5cb44..bf4221a0fc08 100644 --- a/arch/x86/entry/vdso/Makefile +++ b/arch/x86/entry/vdso/Makefile @@ -143,6 +143,7 @@ endif endif $(obj)/vdso32.so.dbg: KBUILD_CFLAGS = $(KBUILD_CFLAGS_32) +$(obj)/vdso32.so.dbg: KBUILD_CFLAGS_KERNEL := $(obj)/vdso32.so.dbg: $(obj)/vdso32/vdso32.lds $(vobjs32) FORCE $(call if_changed,vdso_and_check) diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile index a0fb39abc5c8..70bf0a26da91 100644 --- a/arch/x86/realmode/rm/Makefile +++ b/arch/x86/realmode/rm/Makefile @@ -67,3 +67,4 @@ KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP -D_WAKEUP \ -I$(srctree)/arch/x86/boot KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables +KBUILD_CFLAGS_KERNEL := diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 8ca130af301f..1782b6b87b2d 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -373,6 +373,7 @@ *(DATA_MAIN) \ *(.data..decrypted) \ *(.ref.data) \ + *(.data.rel*) \ *(.data..shared_aligned) /* percpu related */ \ *(.data..unlikely) \ __start_once = .; \ diff --git a/include/linux/hidden.h b/include/linux/hidden.h index 49a17b6b5962..2ad764c0ca18 100644 --- a/include/linux/hidden.h +++ b/include/linux/hidden.h @@ -16,4 +16,6 @@ * giving them 'hidden' visibility. */ +#ifndef __BINDGEN__ #pragma GCC visibility push(hidden) +#endif -- 2.47.3
