From mboxrd@z Thu Jan 1 00:00:00 1970 From: kevin.brodsky@arm.com (Kevin Brodsky) Date: Thu, 27 Oct 2016 17:30:58 +0100 Subject: [RFC PATCH v2 8/8] arm64: Wire up and expose the new compat vDSO In-Reply-To: <20161027163058.12156-1-kevin.brodsky@arm.com> References: <20161027163058.12156-1-kevin.brodsky@arm.com> Message-ID: <20161027163058.12156-9-kevin.brodsky@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Expose the new compat vDSO via the COMPAT_VDSO config option. The option is not enabled in defconfig 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 test. For more flexibility, like CROSS_COMPILE, CROSS_COMPILE_ARM32 can also be set via CONFIG_CROSS_COMPILE_ARM32 (the environment variable overrides the config option). Signed-off-by: Kevin Brodsky --- arch/arm64/Kconfig | 26 ++++++++++++++++++++++++++ arch/arm64/Makefile | 28 ++++++++++++++++++++++++++-- arch/arm64/kernel/Makefile | 8 ++++++-- 3 files changed, 58 insertions(+), 4 deletions(-) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 969ef880d234..883e50def0eb 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1017,6 +1017,32 @@ 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. + +config CROSS_COMPILE_ARM32 + string "32-bit toolchain prefix" + help + Same as setting CROSS_COMPILE_ARM32 in the environment, but saved for + future builds. The environment variable overrides this config option. + endmenu menu "Power management options" diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index 3635b8662724..370d8de0c100 100644 --- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -37,10 +37,32 @@ $(warning LSE atomics not supported by binutils) endif endif -KBUILD_CFLAGS += -mgeneral-regs-only $(lseinstr) +ifeq ($(CONFIG_COMPAT_VDSO), y) + CROSS_COMPILE_ARM32 ?= $(CONFIG_CROSS_COMPILE_ARM32:"%"=%) + + # Check that the user has provided a valid prefix for the 32-bit toolchain. + # To prevent selecting the system gcc by default, the prefix is not allowed to + # be empty, unlike CROSS_COMPILE. In the unlikely event that the system gcc + # is actually the 32-bit ARM compiler to be used, the variable can be set to + # the dirname (e.g. CROSS_COMPILE_ARM32=/usr/bin/). + # Note: this Makefile is read both before and after regenerating the + # config (if needed). Any warning appearing before the config has been + # regenerated should be ignored. + ifeq ($(CROSS_COMPILE_ARM32),) + $(warning CROSS_COMPILE_ARM32 not defined or empty, the compat vDSO will not be built) + else ifeq ($(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 CROSS_COMPILE_ARM32 + 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 @@ -139,6 +161,8 @@ 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)' diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index 7d66bbaafc0c..1487f8cd06dd 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -27,8 +27,11 @@ 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 +arm64-obj-$(CONFIG_COMPAT) += sys32.o signal32.o sys_compat.o \ + entry32.o +ifneq ($(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-$(CONFIG_ARM64_MODULE_PLTS) += module-plts.o @@ -52,6 +55,7 @@ arm64-obj-$(CONFIG_KEXEC) += machine_kexec.o relocate_kernel.o \ cpu-reset.o obj-y += $(arm64-obj-y) vdso/ probes/ +obj-$(CONFIG_VDSO32) += vdso32/ obj-m += $(arm64-obj-m) head-y := head.o extra-y += $(head-y) vmlinux.lds -- 2.10.0