Re: [PATCH v2] vdso: Improve cmd_vdso_check to check all dynamic relocations

Fangrui Song
2023-03-10T19:11:06Z

On 2023-03-10, Vincenzo Frascino wrote:
>Hi Fangrui,
>
>Apologize for the delay, I totally missed that you had a new version of your
>patch since it was threaded with the old one.

Thank you! No worries.

>On 12/21/22 23:51, Fangrui Song wrote:
>> The actual intention is that no dynamic relocation exists. However, some
>> GNU ld ports produce unneeded R_*_NONE. (If a port fails to determine
>> the exact .rel[a].dyn size, the trailing zeros become R_*_NONE
>> relocations. E.g. ld's powerpc port recently fixed
>> https://sourceware.org/bugzilla/show_bug.cgi?id=29540) R_*_NONE are
>> generally no-op in the dynamic loaders. So just ignore them.
>>
>> With the change, we can remove ARCH_REL_TYPE_ABS. ARCH_REL_TYPE_ABS is a
>> bit misnomer as ports may check RELAVETIVE/GLOB_DAT/JUMP_SLOT which are
>> not called "absolute relocations". (The patch is motivated by the arm64
>> port missing R_AARCH64_RELATIVE.)
>
>It makes sense to update the name, it started as "absolute relocations" but then
>it evolved into something else.
>
>A part that, did you perform any testing with the generated vDSO libraries?

I checked that the built vdso did not change (the patch just changes
some post-link verification).

To be more sure, I used commands like
https://github.com/ClangBuiltLinux/tc-build/blob/main/kernel/build.sh#L305
to build a kernel and commands like

~/Dev/ClangBuiltLinux/boot-utils/boot-qemu.py -a arm64 -k /tmp/linux/arm64

to run an image for a couple of architectures.

The initrd images run some init scripts along with

# buildroot/overlay-poweroff/etc/init.d/S50yolo
cat /proc/version
poweroff

I think these have exercised vdso.

>>
>> Signed-off-by: Fangrui Song <maskray@google.com>
>> Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>> ---
>> Change from v1:
>> * rebase after 8ac3b5cd3e0521d92f9755e90d140382fc292510 (lib/vdso: use "grep -E"
>> instead of "egrep")
>> * change the commit message to mention an example GNU ld bug; no longer say the
>> patch fixes a deprecated egrep use
>> ---
>>  arch/arm/vdso/Makefile            |  3 ---
>>  arch/arm64/kernel/vdso/Makefile   |  3 ---
>>  arch/arm64/kernel/vdso32/Makefile |  3 ---
>>  arch/csky/kernel/vdso/Makefile    |  3 ---
>>  arch/loongarch/vdso/Makefile      |  3 ---
>>  arch/mips/vdso/Makefile           |  3 ---
>>  arch/powerpc/kernel/vdso/Makefile |  1 -
>>  arch/riscv/kernel/vdso/Makefile   |  3 ---
>>  arch/s390/kernel/vdso32/Makefile  |  2 --
>>  arch/s390/kernel/vdso64/Makefile  |  2 --
>>  arch/x86/entry/vdso/Makefile      |  4 ----
>>  lib/vdso/Makefile                 | 13 ++++---------
>>  12 files changed, 4 insertions(+), 39 deletions(-)
>>
>> diff --git a/arch/arm/vdso/Makefile b/arch/arm/vdso/Makefile
>> index a7ec06ce3785..e58197bba776 100644
>> --- a/arch/arm/vdso/Makefile
>> +++ b/arch/arm/vdso/Makefile
>> @@ -1,8 +1,5 @@
>>  # SPDX-License-Identifier: GPL-2.0
>>
>> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
>> -# the inclusion of generic Makefile.
>> -ARCH_REL_TYPE_ABS := R_ARM_JUMP_SLOT|R_ARM_GLOB_DAT|R_ARM_ABS32
>
>I would still add a comment here to say why we are including the generic
>Makefile to prevent that it gets accidentally removed (similar thing for every
>architecture touched by this patch).
>
>With that:
>
>Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com> # for vDSO, aarch64
>Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com> # for aarch64
>

Just sent v3
(https://lore.kernel.org/all/20230310190750.3323802-1-maskray@google.com/)
with the comment changes. Thanks!

>>  include $(srctree)/lib/vdso/Makefile
>>
>>  hostprogs := vdsomunge
>> diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
>> index beaf9586338f..1f2427b13410 100644
>> --- a/arch/arm64/kernel/vdso/Makefile
>> +++ b/arch/arm64/kernel/vdso/Makefile
>> @@ -6,9 +6,6 @@
>>  # Heavily based on the vDSO Makefiles for other archs.
>>  #
>>
>> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
>> -# the inclusion of generic Makefile.
>> -ARCH_REL_TYPE_ABS := R_AARCH64_JUMP_SLOT|R_AARCH64_GLOB_DAT|R_AARCH64_ABS64
>>  include $(srctree)/lib/vdso/Makefile
>>
>>  obj-vdso := vgettimeofday.o note.o sigreturn.o
>> diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
>> index f59bd1a4ead6..d014162c5c71 100644
>> --- a/arch/arm64/kernel/vdso32/Makefile
>> +++ b/arch/arm64/kernel/vdso32/Makefile
>> @@ -3,9 +3,6 @@
>>  # Makefile for vdso32
>>  #
>>
>> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
>> -# the inclusion of generic Makefile.
>> -ARCH_REL_TYPE_ABS := R_ARM_JUMP_SLOT|R_ARM_GLOB_DAT|R_ARM_ABS32
>>  include $(srctree)/lib/vdso/Makefile
>>
>>  # Same as cc-*option, but using CC_COMPAT instead of CC
>> diff --git a/arch/csky/kernel/vdso/Makefile b/arch/csky/kernel/vdso/Makefile
>> index 0b6909f10667..86c8c4de1b0f 100644
>> --- a/arch/csky/kernel/vdso/Makefile
>> +++ b/arch/csky/kernel/vdso/Makefile
>> @@ -1,8 +1,5 @@
>>  # SPDX-License-Identifier: GPL-2.0-only
>>
>> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
>> -# the inclusion of generic Makefile.
>> -ARCH_REL_TYPE_ABS := R_CKCORE_ADDR32|R_CKCORE_JUMP_SLOT
>>  include $(srctree)/lib/vdso/Makefile
>>
>>  # Symbols present in the vdso
>> diff --git a/arch/loongarch/vdso/Makefile b/arch/loongarch/vdso/Makefile
>> index d89e2ac75f7b..1b2e0f149f55 100644
>> --- a/arch/loongarch/vdso/Makefile
>> +++ b/arch/loongarch/vdso/Makefile
>> @@ -1,9 +1,6 @@
>>  # SPDX-License-Identifier: GPL-2.0
>>  # Objects to go into the VDSO.
>>
>> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
>> -# the inclusion of generic Makefile.
>> -ARCH_REL_TYPE_ABS := R_LARCH_32|R_LARCH_64|R_LARCH_MARK_LA|R_LARCH_JUMP_SLOT
>>  include $(srctree)/lib/vdso/Makefile
>>
>>  obj-vdso-y := elf.o vgetcpu.o vgettimeofday.o sigreturn.o
>> diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
>> index 1f7d5c6c10b0..c060f3596304 100644
>> --- a/arch/mips/vdso/Makefile
>> +++ b/arch/mips/vdso/Makefile
>> @@ -4,9 +4,6 @@
>>  # Sanitizer runtimes are unavailable and cannot be linked here.
>>   KCSAN_SANITIZE            := n
>>
>> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
>> -# the inclusion of generic Makefile.
>> -ARCH_REL_TYPE_ABS := R_MIPS_JUMP_SLOT|R_MIPS_GLOB_DAT
>>  include $(srctree)/lib/vdso/Makefile
>>
>>  obj-vdso-y := elf.o vgettimeofday.o sigreturn.o
>> diff --git a/arch/powerpc/kernel/vdso/Makefile b/arch/powerpc/kernel/vdso/Makefile
>> index 6a977b0d8ffc..83c347e9136f 100644
>> --- a/arch/powerpc/kernel/vdso/Makefile
>> +++ b/arch/powerpc/kernel/vdso/Makefile
>> @@ -2,7 +2,6 @@
>>
>>  # List of files in the vdso, has to be asm only for now
>>
>> -ARCH_REL_TYPE_ABS :=
>> R_PPC_JUMP_SLOT|R_PPC_GLOB_DAT|R_PPC_ADDR32|R_PPC_ADDR24|R_PPC_ADDR16|R_PPC_ADDR16_LO|R_PPC_ADDR16_HI|R_PPC_ADDR16_HA|R_PPC_ADDR14|R_PPC_ADDR14_BRTAKEN|R_PPC_ADDR14_BRNTAKEN|R_PPC_REL24
>>  include $(srctree)/lib/vdso/Makefile
>>
>>  obj-vdso32 = sigtramp32-32.o gettimeofday-32.o datapage-32.o cacheflush-32.o
>> note-32.o getcpu-32.o
>> diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
>> index 06e6b27f3bcc..d85c37e11b21 100644
>> --- a/arch/riscv/kernel/vdso/Makefile
>> +++ b/arch/riscv/kernel/vdso/Makefile
>> @@ -1,9 +1,6 @@
>>  # SPDX-License-Identifier: GPL-2.0-only
>>  # Copied from arch/tile/kernel/vdso/Makefile
>>
>> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
>> -# the inclusion of generic Makefile.
>> -ARCH_REL_TYPE_ABS := R_RISCV_32|R_RISCV_64|R_RISCV_JUMP_SLOT
>>  include $(srctree)/lib/vdso/Makefile
>>  # Symbols present in the vdso
>>  vdso-syms  = rt_sigreturn
>> diff --git a/arch/s390/kernel/vdso32/Makefile b/arch/s390/kernel/vdso32/Makefile
>> index 245bddfe9bc0..e795fdbbf484 100644
>> --- a/arch/s390/kernel/vdso32/Makefile
>> +++ b/arch/s390/kernel/vdso32/Makefile
>> @@ -2,8 +2,6 @@
>>  # List of files in the vdso
>>
>>  KCOV_INSTRUMENT := n
>> -ARCH_REL_TYPE_ABS := R_390_COPY|R_390_GLOB_DAT|R_390_JMP_SLOT|R_390_RELATIVE
>> -ARCH_REL_TYPE_ABS += R_390_GOT|R_390_PLT
>>
>>  include $(srctree)/lib/vdso/Makefile
>>  obj-vdso32 = vdso_user_wrapper-32.o note-32.o
>> diff --git a/arch/s390/kernel/vdso64/Makefile b/arch/s390/kernel/vdso64/Makefile
>> index 9e2b95a222a9..47dbbfdfad68 100644
>> --- a/arch/s390/kernel/vdso64/Makefile
>> +++ b/arch/s390/kernel/vdso64/Makefile
>> @@ -2,8 +2,6 @@
>>  # List of files in the vdso
>>
>>  KCOV_INSTRUMENT := n
>> -ARCH_REL_TYPE_ABS := R_390_COPY|R_390_GLOB_DAT|R_390_JMP_SLOT|R_390_RELATIVE
>> -ARCH_REL_TYPE_ABS += R_390_GOT|R_390_PLT
>>
>>  include $(srctree)/lib/vdso/Makefile
>>  obj-vdso64 = vdso_user_wrapper.o note.o
>> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
>> index 838613ac15b8..b292c24acb8e 100644
>> --- a/arch/x86/entry/vdso/Makefile
>> +++ b/arch/x86/entry/vdso/Makefile
>> @@ -3,10 +3,6 @@
>>  # Building vDSO images for x86.
>>  #
>>
>> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
>> -# the inclusion of generic Makefile.
>> -ARCH_REL_TYPE_ABS := R_X86_64_JUMP_SLOT|R_X86_64_GLOB_DAT|R_X86_64_RELATIVE|
>> -ARCH_REL_TYPE_ABS += R_386_GLOB_DAT|R_386_JMP_SLOT|R_386_RELATIVE
>>  include $(srctree)/lib/vdso/Makefile
>>
>>  # Sanitizer runtimes are unavailable and cannot be linked here.
>> diff --git a/lib/vdso/Makefile b/lib/vdso/Makefile
>> index e814061d6aa0..9f031eafc465 100644
>> --- a/lib/vdso/Makefile
>> +++ b/lib/vdso/Makefile
>> @@ -5,18 +5,13 @@ GENERIC_VDSO_DIR := $(dir $(GENERIC_VDSO_MK_PATH))
>>
>>  c-gettimeofday-$(CONFIG_GENERIC_GETTIMEOFDAY) := $(addprefix
>> $(GENERIC_VDSO_DIR), gettimeofday.c)
>>
>> -# This cmd checks that the vdso library does not contain absolute relocation
>> +# This cmd checks that the vdso library does not contain dynamic relocations.
>>  # It has to be called after the linking of the vdso library and requires it
>>  # as a parameter.
>>  #
>> -# $(ARCH_REL_TYPE_ABS) is defined in the arch specific makefile and corresponds
>> -# to the absolute relocation types printed by "objdump -R" and accepted by the
>> -# dynamic linker.
>> -ifndef ARCH_REL_TYPE_ABS
>> -$(error ARCH_REL_TYPE_ABS is not set)
>> -endif
>> -
>> +# As a workaround for some GNU ld ports which produce unneeded R_*_NONE
>> +# dynamic relocations, ignore R_*_NONE.
>>  quiet_cmd_vdso_check = VDSOCHK $@
>> -      cmd_vdso_check = if $(OBJDUMP) -R $@ | grep -E -h "$(ARCH_REL_TYPE_ABS)"; \
>> +      cmd_vdso_check = if $(READELF) -rW $@ | grep -v _NONE | grep -q " R_\w*_"; \
>>                 then (echo >&2 "$@: dynamic relocations are not supported"; \
>>                   rm -f $@; /bin/false); fi
>
>--
>Regards,
>Vincenzo