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

From: Fangrui Song
Date: Fri Mar 10 2023 - 14:11:09 EST

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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@xxxxxxxxxx>
Reviewed-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
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@xxxxxxx> # for vDSO, aarch64
Tested-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> # for aarch64

Just sent v3
(https://lore.kernel.org/all/20230310190750.3323802-1-maskray@xxxxxxxxxx/)
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

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In reply to: Vincenzo Frascino: "Re: [PATCH v2] vdso: Improve cmd_vdso_check to check all dynamic relocations"
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