@@ -947,6 +947,26 @@ config SYSVIPC_COMPAT
def_bool y
depends on COMPAT && SYSVIPC
+config COMPAT_VDSO
+ bool "32-bit vDSO"
+ depends on COMPAT
+ default n
+ help
+ Warning: this completely removes the compat vector page, including
+ kuser helpers, which may break 32-bit processes.
+
+ Warning: a 32-bit toolchain is necessary to build the vDSO. You
+ must explicitly define which toolchain should be used by setting
+ CROSS_COMPILE_ARM32 to the prefix of the 32-bit toolchain (same format
+ as CROSS_COMPILE). If a 32-bit compiler cannot be found, a warning
+ will be printed and the kernel will be built as if COMPAT_VDSO had not
+ been set.
+
+ Provide a vDSO to 32-bit processes. It includes the symbols provided
+ by the vDSO from the 32-bit kernel, so that a 32-bit libc can use
+ the compat vDSO without modification. It also provides sigreturn
+ trampolines, and replaces the vector page.
+
endmenu
menu "Power management options"
@@ -30,10 +30,24 @@ $(warning LSE atomics not supported by binutils)
endif
endif
-KBUILD_CFLAGS += -mgeneral-regs-only $(lseinstr)
+ifeq ($(CONFIG_COMPAT_VDSO), y)
+ # Check that the user has provided a valid prefix for arm32 (we allow
+ # CROSS_COMPILE_ARM32 to be defined but empty, in case the system gcc should
+ # be used)
+ ifeq ($(shell [ -v CROSS_COMPILE_ARM32 ] && echo y),)
+ $(warning CROSS_COMPILE_ARM32 not defined, the compat vDSO will not be built)
+ else ifeq ($(shell which $(CROSS_COMPILE_ARM32)gcc 2> /dev/null),)
+ $(warning $(CROSS_COMPILE_ARM32)gcc not found, the compat vDSO will not be built)
+ else
+ export CONFIG_VDSO32 := y
+ vdso32 := -DCONFIG_VDSO32=1
+ endif
+endif
+
+KBUILD_CFLAGS += -mgeneral-regs-only $(lseinstr) $(vdso32)
KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
KBUILD_CFLAGS += $(call cc-option, -mpc-relative-literal-loads)
-KBUILD_AFLAGS += $(lseinstr)
+KBUILD_AFLAGS += $(lseinstr) $(vdso32)
ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
KBUILD_CPPFLAGS += -mbig-endian
@@ -128,6 +142,8 @@ archclean:
prepare: vdso_prepare
vdso_prepare: prepare0
$(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso include/generated/vdso-offsets.h
+ $(if $(CONFIG_VDSO32),$(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso32 \
+ include/generated/vdso32-offsets.h)
define archhelp
echo '* Image.gz - Compressed kernel image (arch/$(ARCH)/boot/Image.gz)'
@@ -25,9 +25,11 @@ OBJCOPYFLAGS := --prefix-symbols=__efistub_
$(obj)/%.stub.o: $(obj)/%.o FORCE
$(call if_changed,objcopy)
-arm64-obj-$(CONFIG_COMPAT) += sys32.o kuser32.o signal32.o \
- sys_compat.o entry32.o \
- ../../arm/kernel/opcodes.o
+arm64-obj-$(CONFIG_COMPAT) += sys32.o signal32.o sys_compat.o \
+ entry32.o ../../arm/kernel/opcodes.o
+ifneq ($(CONFIG_VDSO32),y)
+arm64-obj-y += kuser32.o
+endif
arm64-obj-$(CONFIG_FUNCTION_TRACER) += ftrace.o entry-ftrace.o
arm64-obj-$(CONFIG_MODULES) += arm64ksyms.o module.o
arm64-obj-$(CONFIG_ARM64_MODULE_PLTS) += module-plts.o
@@ -47,6 +49,7 @@ arm64-obj-$(CONFIG_PARAVIRT) += paravirt.o
arm64-obj-$(CONFIG_RANDOMIZE_BASE) += kaslr.o
obj-y += $(arm64-obj-y) vdso/
+obj-$(CONFIG_VDSO32) += vdso32/
obj-m += $(arm64-obj-m)
head-y := head.o
extra-y += $(head-y) vmlinux.lds
Expose the new compat vDSO via the COMPAT_VDSO config option. The option is not enabled by default for two reasons: * The vDSO page replaces the vector page. The vDSO provides its own sigreturn trampolines, replacing those in the vector page, but the kuser helpers are gone. As a result enabling the compat vDSO will break userspace programs relying on the kuser helpers. * We really need a 32-bit compiler this time, and we rely on the user to provide it themselves by setting CROSS_COMPILE_ARM32. Therefore enabling the option by default would make little sense, since the user must explicitly set an environment variable anyway. CONFIG_COMPAT_VDSO is not directly used in the code, because we want to ignore it (build as if it were not set) if the user didn't set CROSS_COMPILE_ARM32 properly. If the variable has been set to a valid prefix, CONFIG_VDSO32 will be set; this is the option that the code and Makefiles will test. Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com> --- arch/arm64/Kconfig | 20 ++++++++++++++++++++ arch/arm64/Makefile | 20 ++++++++++++++++++-- arch/arm64/kernel/Makefile | 9 ++++++--- 3 files changed, 44 insertions(+), 5 deletions(-)