| Message ID | 20230125182201.800076-2-mark.rutland@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: pointer auth cleanup | expand |
On Wed, 25 Jan 2023 at 19:22, Mark Rutland <mark.rutland@arm.com> wrote: > > Assemblers will reject instructions not supported by a target > architecture version, and so we must explicitly tell the assembler the > latest architecture version for which we want to assemble instructions > from. > > We've added a few AS_HAS_ARMV8_<N> definitions for this, in addition to > an inconsistently named AS_HAS_PAC definition, from which arm64's > top-level Makefile determines the architecture version that we intend to > target, and generates the `asm-arch` variable. > > To make this a bit clearer and easier to maintain, this patch reworks > the Makefile to determine asm-arch in a single if-else-endif chain. > AS_HAS_PAC, which is defined when the assembler supports > `-march=armv8.3-a`, is renamed to AS_HAS_ARMV8_3. > > As the logic for armv8.3-a is lifted out of the block handling pointer > authentication, `asm-arch` may now be set to armv8.3-a regardless of > whether support for pointer authentication is selected. This means that > it will be possible to assemble armv8.3-a instructions even if we didn't > intend to, but this is consistent with our handling of other > architecture versions, and the compiler won't generate armv8.3-a > instructions regardless. > > For the moment there's no need for an CONFIG_AS_HAS_ARMV8_1, as the code > for LSE atomics and LDAPR use individual `.arch_extension` entries and > do not require the baseline asm arch to be bumped to armv8.1-a. The > other armv8.1-a features (e.g. PAN) do not require assembler support. > > There should be no functional change as a result of this patch. > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Ard Biesheuvel <ardb@kernel.org> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will@kernel.org> Reviewed-by: Ard Biesheuvel <ardb@kernel.org> > --- > arch/arm64/Kconfig | 4 ++-- > arch/arm64/Makefile | 37 ++++++++++++++++++------------------- > 2 files changed, 20 insertions(+), 21 deletions(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 03934808b2ed0..be760ad7715df 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -1818,7 +1818,7 @@ config ARM64_PTR_AUTH_KERNEL > bool "Use pointer authentication for kernel" > default y > depends on ARM64_PTR_AUTH > - depends on (CC_HAS_SIGN_RETURN_ADDRESS || CC_HAS_BRANCH_PROT_PAC_RET) && AS_HAS_PAC > + depends on (CC_HAS_SIGN_RETURN_ADDRESS || CC_HAS_BRANCH_PROT_PAC_RET) && AS_HAS_ARMV8_3 > # Modern compilers insert a .note.gnu.property section note for PAC > # which is only understood by binutils starting with version 2.33.1. > depends on LD_IS_LLD || LD_VERSION >= 23301 || (CC_IS_GCC && GCC_VERSION < 90100) > @@ -1843,7 +1843,7 @@ config CC_HAS_SIGN_RETURN_ADDRESS > # GCC 7, 8 > def_bool $(cc-option,-msign-return-address=all) > > -config AS_HAS_PAC > +config AS_HAS_ARMV8_3 > def_bool $(cc-option,-Wa$(comma)-march=armv8.3-a) > > config AS_HAS_CFI_NEGATE_RA_STATE > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > index d62bd221828f7..e176eb76345b5 100644 > --- a/arch/arm64/Makefile > +++ b/arch/arm64/Makefile > @@ -63,11 +63,6 @@ stack_protector_prepare: prepare0 > include/generated/asm-offsets.h)) > endif > > -ifeq ($(CONFIG_AS_HAS_ARMV8_2), y) > -# make sure to pass the newest target architecture to -march. > -asm-arch := armv8.2-a > -endif > - > # Ensure that if the compiler supports branch protection we default it > # off, this will be overridden if we are using branch protection. > branch-prot-flags-y += $(call cc-option,-mbranch-protection=none) > @@ -88,25 +83,29 @@ branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET_BTI) := -mbranch-protectio > else > branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=$(PACRET-y) > endif > -# -march=armv8.3-a enables the non-nops instructions for PAC, to avoid the > -# compiler to generate them and consequently to break the single image contract > -# we pass it only to the assembler. This option is utilized only in case of non > -# integrated assemblers. > -ifeq ($(CONFIG_AS_HAS_PAC), y) > -asm-arch := armv8.3-a > -endif > endif > > KBUILD_CFLAGS += $(branch-prot-flags-y) > > -ifeq ($(CONFIG_AS_HAS_ARMV8_4), y) > -# make sure to pass the newest target architecture to -march. > -asm-arch := armv8.4-a > -endif > - > +# Tell the assembler to support instructions from the latest target > +# architecture. > +# > +# For non-integrated assemblers we'll pass this on the command line, and for > +# integrated assemblers we'll define ARM64_ASM_ARCH and ARM64_ASM_PREAMBLE for > +# inline usage. > +# > +# We cannot pass the same arch flag to the compiler as this would allow it to > +# freely generate instructions which are not supported by earlier architecture > +# versions, which would prevent a single kernel image from working on earlier > +# hardware. > ifeq ($(CONFIG_AS_HAS_ARMV8_5), y) > -# make sure to pass the newest target architecture to -march. > -asm-arch := armv8.5-a > + asm-arch := armv8.5-a > +else ifeq ($(CONFIG_AS_HAS_ARMV8_4), y) > + asm-arch := armv8.4-a > +else ifeq ($(CONFIG_AS_HAS_ARMV8_3), y) > + asm-arch := armv8.3-a > +else ifeq ($(CONFIG_AS_HAS_ARMV8_2), y) > + asm-arch := armv8.2-a > endif > > ifdef asm-arch > -- > 2.30.2 >
On Wed, Jan 25, 2023 at 06:22:00PM +0000, Mark Rutland wrote: > Assemblers will reject instructions not supported by a target > architecture version, and so we must explicitly tell the assembler the > latest architecture version for which we want to assemble instructions > from. Reviewed-by: Mark Brown <broonie@kernel.org>
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 03934808b2ed0..be760ad7715df 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1818,7 +1818,7 @@ config ARM64_PTR_AUTH_KERNEL bool "Use pointer authentication for kernel" default y depends on ARM64_PTR_AUTH - depends on (CC_HAS_SIGN_RETURN_ADDRESS || CC_HAS_BRANCH_PROT_PAC_RET) && AS_HAS_PAC + depends on (CC_HAS_SIGN_RETURN_ADDRESS || CC_HAS_BRANCH_PROT_PAC_RET) && AS_HAS_ARMV8_3 # Modern compilers insert a .note.gnu.property section note for PAC # which is only understood by binutils starting with version 2.33.1. depends on LD_IS_LLD || LD_VERSION >= 23301 || (CC_IS_GCC && GCC_VERSION < 90100) @@ -1843,7 +1843,7 @@ config CC_HAS_SIGN_RETURN_ADDRESS # GCC 7, 8 def_bool $(cc-option,-msign-return-address=all) -config AS_HAS_PAC +config AS_HAS_ARMV8_3 def_bool $(cc-option,-Wa$(comma)-march=armv8.3-a) config AS_HAS_CFI_NEGATE_RA_STATE diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index d62bd221828f7..e176eb76345b5 100644 --- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -63,11 +63,6 @@ stack_protector_prepare: prepare0 include/generated/asm-offsets.h)) endif -ifeq ($(CONFIG_AS_HAS_ARMV8_2), y) -# make sure to pass the newest target architecture to -march. -asm-arch := armv8.2-a -endif - # Ensure that if the compiler supports branch protection we default it # off, this will be overridden if we are using branch protection. branch-prot-flags-y += $(call cc-option,-mbranch-protection=none) @@ -88,25 +83,29 @@ branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET_BTI) := -mbranch-protectio else branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=$(PACRET-y) endif -# -march=armv8.3-a enables the non-nops instructions for PAC, to avoid the -# compiler to generate them and consequently to break the single image contract -# we pass it only to the assembler. This option is utilized only in case of non -# integrated assemblers. -ifeq ($(CONFIG_AS_HAS_PAC), y) -asm-arch := armv8.3-a -endif endif KBUILD_CFLAGS += $(branch-prot-flags-y) -ifeq ($(CONFIG_AS_HAS_ARMV8_4), y) -# make sure to pass the newest target architecture to -march. -asm-arch := armv8.4-a -endif - +# Tell the assembler to support instructions from the latest target +# architecture. +# +# For non-integrated assemblers we'll pass this on the command line, and for +# integrated assemblers we'll define ARM64_ASM_ARCH and ARM64_ASM_PREAMBLE for +# inline usage. +# +# We cannot pass the same arch flag to the compiler as this would allow it to +# freely generate instructions which are not supported by earlier architecture +# versions, which would prevent a single kernel image from working on earlier +# hardware. ifeq ($(CONFIG_AS_HAS_ARMV8_5), y) -# make sure to pass the newest target architecture to -march. -asm-arch := armv8.5-a + asm-arch := armv8.5-a +else ifeq ($(CONFIG_AS_HAS_ARMV8_4), y) + asm-arch := armv8.4-a +else ifeq ($(CONFIG_AS_HAS_ARMV8_3), y) + asm-arch := armv8.3-a +else ifeq ($(CONFIG_AS_HAS_ARMV8_2), y) + asm-arch := armv8.2-a endif ifdef asm-arch
Assemblers will reject instructions not supported by a target architecture version, and so we must explicitly tell the assembler the latest architecture version for which we want to assemble instructions from. We've added a few AS_HAS_ARMV8_<N> definitions for this, in addition to an inconsistently named AS_HAS_PAC definition, from which arm64's top-level Makefile determines the architecture version that we intend to target, and generates the `asm-arch` variable. To make this a bit clearer and easier to maintain, this patch reworks the Makefile to determine asm-arch in a single if-else-endif chain. AS_HAS_PAC, which is defined when the assembler supports `-march=armv8.3-a`, is renamed to AS_HAS_ARMV8_3. As the logic for armv8.3-a is lifted out of the block handling pointer authentication, `asm-arch` may now be set to armv8.3-a regardless of whether support for pointer authentication is selected. This means that it will be possible to assemble armv8.3-a instructions even if we didn't intend to, but this is consistent with our handling of other architecture versions, and the compiler won't generate armv8.3-a instructions regardless. For the moment there's no need for an CONFIG_AS_HAS_ARMV8_1, as the code for LSE atomics and LDAPR use individual `.arch_extension` entries and do not require the baseline asm arch to be bumped to armv8.1-a. The other armv8.1-a features (e.g. PAN) do not require assembler support. There should be no functional change as a result of this patch. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Ard Biesheuvel <ardb@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> --- arch/arm64/Kconfig | 4 ++-- arch/arm64/Makefile | 37 ++++++++++++++++++------------------- 2 files changed, 20 insertions(+), 21 deletions(-)