From: Sami Tolvanen <samitolvanen@google.com> To: Masahiro Yamada <masahiroy@kernel.org>, Will Deacon <will@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org>, Steven Rostedt <rostedt@goodmis.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, "Paul E. McKenney" <paulmck@kernel.org>, Kees Cook <keescook@chromium.org>, Nick Desaulniers <ndesaulniers@google.com>, clang-built-linux@googlegroups.com, kernel-hardening@lists.openwall.com, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, x86@kernel.org, Arvind Sankar <nivedita@alum.mit.edu> Subject: [PATCH v3 03/30] x86/boot/compressed: Disable relocation relaxation Date: Fri, 18 Sep 2020 13:14:09 -0700 [thread overview] Message-ID: <20200918201436.2932360-4-samitolvanen@google.com> (raw) In-Reply-To: <20200918201436.2932360-1-samitolvanen@google.com> From: Arvind Sankar <nivedita@alum.mit.edu> The x86-64 psABI [0] specifies special relocation types (R_X86_64_[REX_]GOTPCRELX) for indirection through the Global Offset Table, semantically equivalent to R_X86_64_GOTPCREL, which the linker can take advantage of for optimization (relaxation) at link time. This is supported by LLD and binutils versions 2.26 onwards. The compressed kernel is position-independent code, however, when using LLD or binutils versions before 2.27, it must be linked without the -pie option. In this case, the linker may optimize certain instructions into a non-position-independent form, by converting foo@GOTPCREL(%rip) to $foo. This potential issue has been present with LLD and binutils-2.26 for a long time, but it has never manifested itself before now: - LLD and binutils-2.26 only relax movq foo@GOTPCREL(%rip), %reg to leaq foo(%rip), %reg which is still position-independent, rather than mov $foo, %reg which is permitted by the psABI when -pie is not enabled. - gcc happens to only generate GOTPCREL relocations on mov instructions. - clang does generate GOTPCREL relocations on non-mov instructions, but when building the compressed kernel, it uses its integrated assembler (due to the redefinition of KBUILD_CFLAGS dropping -no-integrated-as), which has so far defaulted to not generating the GOTPCRELX relocations. Nick Desaulniers reports [1,2]: A recent change [3] to a default value of configuration variable (ENABLE_X86_RELAX_RELOCATIONS OFF -> ON) in LLVM now causes Clang's integrated assembler to emit R_X86_64_GOTPCRELX/R_X86_64_REX_GOTPCRELX relocations. LLD will relax instructions with these relocations based on whether the image is being linked as position independent or not. When not, then LLD will relax these instructions to use absolute addressing mode (R_RELAX_GOT_PC_NOPIC). This causes kernels built with Clang and linked with LLD to fail to boot. Patch series [4] is a solution to allow the compressed kernel to be linked with -pie unconditionally, but even if merged is unlikely to be backported. As a simple solution that can be applied to stable as well, prevent the assembler from generating the relaxed relocation types using the -mrelax-relocations=no option. For ease of backporting, do this unconditionally. [0] https://gitlab.com/x86-psABIs/x86-64-ABI/-/blob/master/x86-64-ABI/linker-optimization.tex#L65 [1] https://lore.kernel.org/lkml/20200807194100.3570838-1-ndesaulniers@google.com/ [2] https://github.com/ClangBuiltLinux/linux/issues/1121 [3] https://reviews.llvm.org/rGc41a18cf61790fc898dcda1055c3efbf442c14c0 [4] https://lore.kernel.org/lkml/20200731202738.2577854-1-nivedita@alum.mit.edu/ Reported-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu> Tested-by: Nick Desaulniers <ndesaulniers@google.com> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Cc: stable@vger.kernel.org --- arch/x86/boot/compressed/Makefile | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 3962f592633d..ff7894f39e0e 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -43,6 +43,8 @@ KBUILD_CFLAGS += -Wno-pointer-sign KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) KBUILD_CFLAGS += -fno-asynchronous-unwind-tables KBUILD_CFLAGS += -D__DISABLE_EXPORTS +# Disable relocation relaxation in case the link is not PIE. +KBUILD_CFLAGS += $(call as-option,-Wa$(comma)-mrelax-relocations=no) KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ GCOV_PROFILE := n -- 2.28.0.681.g6f77f65b4e-goog
WARNING: multiple messages have this Message-ID (diff)
From: Sami Tolvanen <samitolvanen@google.com> To: Masahiro Yamada <masahiroy@kernel.org>, Will Deacon <will@kernel.org> Cc: linux-arch@vger.kernel.org, x86@kernel.org, Kees Cook <keescook@chromium.org>, "Paul E. McKenney" <paulmck@kernel.org>, kernel-hardening@lists.openwall.com, Peter Zijlstra <peterz@infradead.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, linux-kbuild@vger.kernel.org, Nick Desaulniers <ndesaulniers@google.com>, linux-kernel@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>, clang-built-linux@googlegroups.com, Arvind Sankar <nivedita@alum.mit.edu>, linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: [PATCH v3 03/30] x86/boot/compressed: Disable relocation relaxation Date: Fri, 18 Sep 2020 13:14:09 -0700 [thread overview] Message-ID: <20200918201436.2932360-4-samitolvanen@google.com> (raw) In-Reply-To: <20200918201436.2932360-1-samitolvanen@google.com> From: Arvind Sankar <nivedita@alum.mit.edu> The x86-64 psABI [0] specifies special relocation types (R_X86_64_[REX_]GOTPCRELX) for indirection through the Global Offset Table, semantically equivalent to R_X86_64_GOTPCREL, which the linker can take advantage of for optimization (relaxation) at link time. This is supported by LLD and binutils versions 2.26 onwards. The compressed kernel is position-independent code, however, when using LLD or binutils versions before 2.27, it must be linked without the -pie option. In this case, the linker may optimize certain instructions into a non-position-independent form, by converting foo@GOTPCREL(%rip) to $foo. This potential issue has been present with LLD and binutils-2.26 for a long time, but it has never manifested itself before now: - LLD and binutils-2.26 only relax movq foo@GOTPCREL(%rip), %reg to leaq foo(%rip), %reg which is still position-independent, rather than mov $foo, %reg which is permitted by the psABI when -pie is not enabled. - gcc happens to only generate GOTPCREL relocations on mov instructions. - clang does generate GOTPCREL relocations on non-mov instructions, but when building the compressed kernel, it uses its integrated assembler (due to the redefinition of KBUILD_CFLAGS dropping -no-integrated-as), which has so far defaulted to not generating the GOTPCRELX relocations. Nick Desaulniers reports [1,2]: A recent change [3] to a default value of configuration variable (ENABLE_X86_RELAX_RELOCATIONS OFF -> ON) in LLVM now causes Clang's integrated assembler to emit R_X86_64_GOTPCRELX/R_X86_64_REX_GOTPCRELX relocations. LLD will relax instructions with these relocations based on whether the image is being linked as position independent or not. When not, then LLD will relax these instructions to use absolute addressing mode (R_RELAX_GOT_PC_NOPIC). This causes kernels built with Clang and linked with LLD to fail to boot. Patch series [4] is a solution to allow the compressed kernel to be linked with -pie unconditionally, but even if merged is unlikely to be backported. As a simple solution that can be applied to stable as well, prevent the assembler from generating the relaxed relocation types using the -mrelax-relocations=no option. For ease of backporting, do this unconditionally. [0] https://gitlab.com/x86-psABIs/x86-64-ABI/-/blob/master/x86-64-ABI/linker-optimization.tex#L65 [1] https://lore.kernel.org/lkml/20200807194100.3570838-1-ndesaulniers@google.com/ [2] https://github.com/ClangBuiltLinux/linux/issues/1121 [3] https://reviews.llvm.org/rGc41a18cf61790fc898dcda1055c3efbf442c14c0 [4] https://lore.kernel.org/lkml/20200731202738.2577854-1-nivedita@alum.mit.edu/ Reported-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu> Tested-by: Nick Desaulniers <ndesaulniers@google.com> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Cc: stable@vger.kernel.org --- arch/x86/boot/compressed/Makefile | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 3962f592633d..ff7894f39e0e 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -43,6 +43,8 @@ KBUILD_CFLAGS += -Wno-pointer-sign KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) KBUILD_CFLAGS += -fno-asynchronous-unwind-tables KBUILD_CFLAGS += -D__DISABLE_EXPORTS +# Disable relocation relaxation in case the link is not PIE. +KBUILD_CFLAGS += $(call as-option,-Wa$(comma)-mrelax-relocations=no) KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ GCOV_PROFILE := n -- 2.28.0.681.g6f77f65b4e-goog _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-09-18 20:14 UTC|newest] Thread overview: 113+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-09-18 20:14 [PATCH v3 00/30] Add support for Clang LTO Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 01/30] lib/string.c: implement stpcpy Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 02/30] RAS/CEC: Fix cec_init() prototype Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen [this message] 2020-09-18 20:14 ` [PATCH v3 03/30] x86/boot/compressed: Disable relocation relaxation Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-21 15:53 ` Nick Desaulniers 2020-09-21 15:53 ` Nick Desaulniers 2020-09-21 15:53 ` Nick Desaulniers 2020-09-18 20:14 ` [PATCH v3 04/30] x86/asm: Replace __force_order with memory clobber Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 05/30] kbuild: preprocess module linker script Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 06/30] objtool: Add a pass for generating __mcount_loc Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 07/30] objtool: Don't autodetect vmlinux.o Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 08/30] kbuild: add support for objtool mcount Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 09/30] x86, build: use " Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 10/30] treewide: remove DISABLE_LTO Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 11/30] kbuild: add support for Clang LTO Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 12/30] kbuild: lto: fix module versioning Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 13/30] kbuild: lto: postpone objtool Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 21:27 ` Kees Cook 2020-09-18 21:27 ` Kees Cook 2020-09-21 18:58 ` Sami Tolvanen 2020-09-21 18:58 ` Sami Tolvanen 2020-09-21 18:58 ` Sami Tolvanen 2020-09-19 7:01 ` kernel test robot 2020-09-18 20:14 ` [PATCH v3 14/30] kbuild: lto: limit inlining Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 15/30] kbuild: lto: merge module sections Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 16/30] kbuild: lto: remove duplicate dependencies from .mod files Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 17/30] init: lto: ensure initcall ordering Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 21:29 ` Kees Cook 2020-09-18 21:29 ` Kees Cook 2020-09-18 20:14 ` [PATCH v3 18/30] init: lto: fix PREL32 relocations Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 19/30] PCI: Fix PREL32 relocations for LTO Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 20/30] modpost: lto: strip .lto from module names Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 21/30] scripts/mod: disable LTO for empty.c Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 22/30] efi/libstub: disable LTO Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 23/30] drivers/misc/lkdtm: disable LTO for rodata.o Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 24/30] arm64: export CC_USING_PATCHABLE_FUNCTION_ENTRY Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 25/30] arm64: vdso: disable LTO Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 26/30] KVM: arm64: disable LTO for the nVHE directory Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 27/30] arm64: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 28/30] x86, vdso: disable LTO only for vDSO Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 29/30] x86, cpu: disable LTO for cpu.c Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` [PATCH v3 30/30] x86, build: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:14 ` Sami Tolvanen 2020-09-18 20:22 ` [PATCH v3 00/30] Add support for Clang LTO Sedat Dilek 2020-09-18 20:22 ` Sedat Dilek 2020-09-18 20:22 ` Sedat Dilek 2020-09-18 20:50 ` Sami Tolvanen 2020-09-18 20:50 ` Sami Tolvanen 2020-09-18 20:50 ` Sami Tolvanen 2020-09-18 20:53 ` Nick Desaulniers 2020-09-18 20:53 ` Nick Desaulniers 2020-09-18 20:53 ` Nick Desaulniers
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20200918201436.2932360-4-samitolvanen@google.com \ --to=samitolvanen@google.com \ --cc=clang-built-linux@googlegroups.com \ --cc=gregkh@linuxfoundation.org \ --cc=keescook@chromium.org \ --cc=kernel-hardening@lists.openwall.com \ --cc=linux-arch@vger.kernel.org \ --cc=linux-arm-kernel@lists.infradead.org \ --cc=linux-kbuild@vger.kernel.org \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-pci@vger.kernel.org \ --cc=masahiroy@kernel.org \ --cc=ndesaulniers@google.com \ --cc=nivedita@alum.mit.edu \ --cc=paulmck@kernel.org \ --cc=peterz@infradead.org \ --cc=rostedt@goodmis.org \ --cc=will@kernel.org \ --cc=x86@kernel.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.