@@ -2132,6 +2132,13 @@ config X86_GLOBAL_STACKPROTECTOR
bool
depends on CC_STACKPROTECTOR
+config X86_PIE
+ bool
+ depends on X86_64 && !XEN_PVH
+ select DEFAULT_HIDDEN
+ select MODULE_REL_CRCS if MODVERSIONS
+ select X86_GLOBAL_STACKPROTECTOR if CC_STACKPROTECTOR
+
config HOTPLUG_CPU
bool "Support for hot-pluggable CPUs"
depends on SMP
@@ -45,8 +45,12 @@ export REALMODE_CFLAGS
export BITS
ifdef CONFIG_X86_NEED_RELOCS
+ifdef CONFIG_X86_PIE
+ LDFLAGS_vmlinux := -pie -shared -Bsymbolic
+else
LDFLAGS_vmlinux := --emit-relocs
endif
+endif
#
# Prevent GCC from generating any FP code by mistake.
@@ -141,7 +145,12 @@ else
KBUILD_CFLAGS += $(cflags-y)
KBUILD_CFLAGS += -mno-red-zone
+ifdef CONFIG_X86_PIE
+ KBUILD_CFLAGS += -fPIC
+ KBUILD_CFLAGS_MODULE += -fno-PIC -mcmodel=kernel
+else
KBUILD_CFLAGS += -mcmodel=kernel
+endif
# -funit-at-a-time shrinks the kernel .text considerably
# unfortunately it makes reading oopses harder.
Add the CONFIG_X86_PIE option which builds the kernel as a Position Independent Executable (PIE). The kernel is currently build with the mcmodel=kernel option which forces it to stay on the top 2G of the virtual address space. With PIE, the kernel will be able to move below the -2G limit increasing the KASLR range from 1GB to 3GB. The modules do not support PIE due to how they are linked. Disable PIE for them and default to mcmodel=kernel for now. The PIE configuration is not yet compatible with XEN_PVH. Xen PVH generates 32-bit assembly and uses a long jump to transition to 64-bit. A long jump require an absolute reference that is not compatible with PIE. Performance/Size impact: Hackbench (50% and 1600% loads): - PIE disabled: no significant change (-0.50% / +0.50%) - PIE enabled: 7% to 8% on half load, 10% on heavy load. These results are aligned with the different research on user-mode PIE impact on cpu intensive benchmarks (around 10% on x86_64). slab_test (average of 10 runs): - PIE disabled: no significant change (-1% / +1%) - PIE enabled: 3% to 4% Kernbench (average of 10 Half and Optimal runs): Elapsed Time: - PIE disabled: no significant change (-0.22% / +0.06%) - PIE enabled: around 0.50% System Time: - PIE disabled: no significant change (-0.99% / -1.28%) - PIE enabled: 5% to 6% Size of vmlinux (Ubuntu configuration): File size: - PIE disabled: 472928672 bytes (-0.000169% from baseline) - PIE enabled: 216878461 bytes (-54.14% from baseline) .text sections: - PIE disabled: 9373572 bytes (+0.04% from baseline) - PIE enabled: 9499138 bytes (+1.38% from baseline) The big decrease in vmlinux file size is due to the lower number of relocations appended to the file. Signed-off-by: Thomas Garnier <thgarnie@google.com> --- arch/x86/Kconfig | 7 +++++++ arch/x86/Makefile | 9 +++++++++ 2 files changed, 16 insertions(+)