From: Fangrui Song <maskray@google.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Arvind Sankar <nivedita@alum.mit.edu>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Dmitry Golovin <dima@golovin.in>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Masahiro Yamada <masahiroy@kernel.org>,
Daniel Kiper <daniel.kiper@oracle.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 4/4] x86/boot: Check that there are no runtime relocations
Date: Mon, 25 May 2020 09:26:26 -0700 [thread overview]
Message-ID: <20200525162626.4covxuycii6bvmjg@google.com> (raw)
In-Reply-To: <CAMj1kXFjDMuLekYKiPoKDqJhfkY8UViApdMd3JaPmGbnKLO+NA@mail.gmail.com>
On 2020-05-25, Ard Biesheuvel wrote:
>On Sun, 24 May 2020 at 23:28, Arvind Sankar <nivedita@alum.mit.edu> wrote:
>>
>> Add a linker script check that there are no runtime relocations, and
>> remove the old one that tries to check via looking for specially-named
>> sections in the object files.
>>
>> Drop the tests for -fPIE compiler option and -pie linker option, as they
>> are available in all supported gcc and binutils versions (as well as
>> clang and lld).
>>
>> Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
>> ---
>> arch/x86/boot/compressed/Makefile | 28 +++-----------------------
>> arch/x86/boot/compressed/vmlinux.lds.S | 11 ++++++++++
>> 2 files changed, 14 insertions(+), 25 deletions(-)
>>
>> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
>> index d3e882e855ee..679a2b383bfe 100644
>> --- a/arch/x86/boot/compressed/Makefile
>> +++ b/arch/x86/boot/compressed/Makefile
>> @@ -27,7 +27,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \
>> vmlinux.bin.xz vmlinux.bin.lzo vmlinux.bin.lz4
>>
>> KBUILD_CFLAGS := -m$(BITS) -O2
>> -KBUILD_CFLAGS += -fno-strict-aliasing $(call cc-option, -fPIE, -fPIC)
>> +KBUILD_CFLAGS += -fno-strict-aliasing -fPIE
>> KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
>> cflags-$(CONFIG_X86_32) := -march=i386
>> cflags-$(CONFIG_X86_64) := -mcmodel=small
>> @@ -49,7 +49,7 @@ UBSAN_SANITIZE :=n
>> KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
>> # Compressed kernel should be built as PIE since it may be loaded at any
>> # address by the bootloader.
>> -KBUILD_LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
>> +KBUILD_LDFLAGS += -pie $(call ld-option, --no-dynamic-linker)
>> LDFLAGS_vmlinux := -T
>>
>> hostprogs := mkpiggy
>> @@ -84,30 +84,8 @@ vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
>> vmlinux-objs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
>> vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_thunk_$(BITS).o
>>
>> -# The compressed kernel is built with -fPIC/-fPIE so that a boot loader
>> -# can place it anywhere in memory and it will still run. However, since
>> -# it is executed as-is without any ELF relocation processing performed
>> -# (and has already had all relocation sections stripped from the binary),
>> -# none of the code can use data relocations (e.g. static assignments of
>> -# pointer values), since they will be meaningless at runtime. This check
>> -# will refuse to link the vmlinux if any of these relocations are found.
>> -quiet_cmd_check_data_rel = DATAREL $@
>> -define cmd_check_data_rel
>> - for obj in $(filter %.o,$^); do \
>> - $(READELF) -S $$obj | grep -qF .rel.local && { \
>> - echo "error: $$obj has data relocations!" >&2; \
>> - exit 1; \
>> - } || true; \
>> - done
>> -endef
>> -
>> -# We need to run two commands under "if_changed", so merge them into a
>> -# single invocation.
>> -quiet_cmd_check-and-link-vmlinux = LD $@
>> - cmd_check-and-link-vmlinux = $(cmd_check_data_rel); $(cmd_ld)
>> -
>> $(obj)/vmlinux: $(vmlinux-objs-y) FORCE
>> - $(call if_changed,check-and-link-vmlinux)
>> + $(call if_changed,ld)
>>
>> OBJCOPYFLAGS_vmlinux.bin := -R .comment -S
>> $(obj)/vmlinux.bin: vmlinux FORCE
>> diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
>> index d826ab38a8f9..0ac14feacb24 100644
>> --- a/arch/x86/boot/compressed/vmlinux.lds.S
>> +++ b/arch/x86/boot/compressed/vmlinux.lds.S
>> @@ -11,9 +11,15 @@ OUTPUT_FORMAT(CONFIG_OUTPUT_FORMAT)
>> #ifdef CONFIG_X86_64
>> OUTPUT_ARCH(i386:x86-64)
>> ENTRY(startup_64)
>> +
>> +#define REL .rela
>> +
>> #else
>> OUTPUT_ARCH(i386)
>> ENTRY(startup_32)
>> +
>> +#define REL .rel
>> +
>> #endif
>>
>> SECTIONS
>> @@ -42,6 +48,9 @@ SECTIONS
>> *(.rodata.*)
>> _erodata = . ;
>> }
>> + REL.dyn : {
>> + *(REL.*)
>> + }
>
>Do we really need the macro here? Could we just do
The output section name does not matter: it will be discarded by the linker.
>.rel.dyn : { *(.rel.* .rela.*) }
If for some reasons there is at least one SHT_REL and at least one
SHT_RELA, LLD will error "section type mismatch for .rel.dyn", while the
intended diagnostic is the assert below.
>(or even
>
>.rel.dyn : { *(.rel.* }
>.rela.dyn : { *(.rela.*) }
>
>if the output section name matters, and always assert that both are empty)?
.rel.dyn : { *(.rel.* }
.rela.dyn : { *(.rela.*) }
looks good to me.
FWIW I intend to add -z rel and -z rela to LLD: https://reviews.llvm.org/D80496#inline-738804
(binutils thread https://sourceware.org/pipermail/binutils/2020-May/111244.html)
In case someone builds the x86-64 kernel with -z rel, your suggested
input section description will work out of the box...
>> .got : {
>> *(.got)
>> }
>> @@ -83,3 +92,5 @@ ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, "Unexpected GOT/PLT en
>> #else
>> ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0xc, "Unexpected GOT/PLT entries detected!")
>> #endif
>> +
>> +ASSERT(SIZEOF(REL.dyn) == 0, "Unexpected runtime relocations detected!")
>> --
>> 2.26.2
>>
next prev parent reply other threads:[~2020-05-25 16:26 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-01 8:42 [PATCH] x86/boot: allow a relocatable kernel to be linked with lld Dmitry Golovin
2020-05-02 3:43 ` Nathan Chancellor
2020-05-15 18:50 ` Borislav Petkov
[not found] ` <602331589572661@mail.yandex.ru>
2020-05-17 19:44 ` Fangrui Song
2020-05-17 20:25 ` Arvind Sankar
2020-05-18 19:10 ` Nick Desaulniers
2020-05-24 21:28 ` [PATCH 0/4] x86/boot: Remove runtime relocations from compressed kernel Arvind Sankar
2020-05-25 7:10 ` Ard Biesheuvel
2020-05-25 22:59 ` [PATCH v2 " Arvind Sankar
2020-05-26 12:29 ` Sedat Dilek
2020-05-26 12:30 ` Ard Biesheuvel
2020-05-26 12:33 ` Sedat Dilek
2020-05-26 12:44 ` Sedat Dilek
2020-05-26 14:47 ` Arvind Sankar
2020-05-26 14:50 ` Sedat Dilek
2020-05-26 15:36 ` Arvind Sankar
2020-05-26 15:38 ` Sedat Dilek
2020-05-27 6:26 ` Sedat Dilek
2020-05-26 14:48 ` Sedat Dilek
2020-05-26 14:55 ` Sedat Dilek
2020-05-26 15:07 ` Sedat Dilek
2020-05-26 15:31 ` Arvind Sankar
2020-05-27 6:24 ` Sedat Dilek
2020-05-26 16:18 ` Sedat Dilek
2020-05-25 22:59 ` [PATCH v2 1/4] x86/boot: Add .text.* to setup.ld Arvind Sankar
2020-05-25 22:59 ` [PATCH v2 2/4] x86/boot: Remove run-time relocations from .head.text code Arvind Sankar
2020-05-25 22:59 ` [PATCH v2 3/4] x86/boot: Remove runtime relocations from head_{32,64}.S Arvind Sankar
2020-05-25 22:59 ` [PATCH v2 4/4] x86/boot: Check that there are no runtime relocations Arvind Sankar
2020-05-26 6:11 ` Ard Biesheuvel
2020-05-26 15:16 ` Arvind Sankar
2020-05-26 17:13 ` Fangrui Song
2020-05-26 19:14 ` Arvind Sankar
2020-08-06 11:19 ` Andy Shevchenko
2020-08-06 16:12 ` Arvind Sankar
2020-05-26 0:37 ` [PATCH 0/4] x86/boot: Remove runtime relocations from compressed kernel Fangrui Song
2020-05-24 21:28 ` [PATCH 1/4] x86/boot: Add .text.startup to setup.ld Arvind Sankar
2020-05-24 22:13 ` Fangrui Song
2020-05-24 23:00 ` Arvind Sankar
2020-05-24 23:49 ` Fangrui Song
2020-05-24 22:48 ` Brian Gerst
2020-05-24 21:28 ` [PATCH 2/4] x86/boot: Remove runtime relocations from .head.text code Arvind Sankar
2020-05-24 22:53 ` Fangrui Song
2020-05-24 23:44 ` Arvind Sankar
2020-05-25 0:55 ` Fangrui Song
2020-05-24 21:28 ` [PATCH 3/4] x86/boot: Remove runtime relocations from head_{32,64}.S Arvind Sankar
2020-05-24 23:22 ` Fangrui Song
2020-05-24 23:58 ` Arvind Sankar
2020-05-24 21:28 ` [PATCH 4/4] x86/boot: Check that there are no runtime relocations Arvind Sankar
2020-05-24 23:36 ` Fangrui Song
2020-05-24 23:57 ` Arvind Sankar
2020-05-25 6:10 ` Ard Biesheuvel
2020-05-25 16:26 ` Fangrui Song [this message]
2020-05-25 19:22 ` Arvind Sankar
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