From 3631280713464ab9078bde9e6467f244f897c204 Mon Sep 17 00:00:00 2001

From: Saleem Abdulrasool <abdulras@google.com>

Date: Wed, 4 Aug 2021 17:32:14 +0000

Subject: [PATCH] riscv: explicitly use symbol offsets for VDSO

Git-commit: fde9c59aebafb91caeed816cc510b56f14aa63ae

Patch-mainline: v5.15-rc1

References: stable-5.14.12

[ Upstream commit fde9c59aebafb91caeed816cc510b56f14aa63ae ]

The current implementation of the `__rt_sigaction` reference computed an

absolute offset relative to the mapped base of the VDSO.  While this can

be handled in the medlow model, the medany model cannot handle this as

it is meant to be position independent.  The current implementation

relied on the BFD linker relaxing the PC-relative relocation into an

absolute relocation as it was a near-zero address allowing it to be

referenced relative to `zero`.

We now extract the offsets and create a generated header allowing the

build with LLVM and lld to succeed as we no longer depend on the linker

rewriting address references near zero.  This change was largely

modelled after the ARM64 target which does something similar.

Signed-off-by: Saleem Abdulrasool <abdulras@google.com>

Tested-by: Nathan Chancellor <nathan@kernel.org>

Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

Signed-off-by: Sasha Levin <sashal@kernel.org>

Acked-by: Takashi Iwai <tiwai@suse.de>

---

 arch/riscv/Makefile                        |  4 ++++

 arch/riscv/include/asm/vdso.h              | 14 ++----------

 arch/riscv/kernel/vdso/Makefile            | 25 ++++++++++------------

 arch/riscv/kernel/vdso/gen_vdso_offsets.sh |  5 +++++

 arch/riscv/kernel/vdso/so2s.sh             |  6 ------

 5 files changed, 22 insertions(+), 32 deletions(-)

 create mode 100755 arch/riscv/kernel/vdso/gen_vdso_offsets.sh

 delete mode 100755 arch/riscv/kernel/vdso/so2s.sh

diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile

index bc74afdbf31e..e026b2d0a5a4 100644

--- a/arch/riscv/Makefile

+++ b/arch/riscv/Makefile

@@ -108,6 +108,10 @@ PHONY += vdso_install

 vdso_install:

 	$(Q)$(MAKE) $(build)=arch/riscv/kernel/vdso $@

+prepare: vdso_prepare

+vdso_prepare: prepare0

+	$(Q)$(MAKE) $(build)=arch/riscv/kernel/vdso include/generated/vdso-offsets.h

+

 ifneq ($(CONFIG_XIP_KERNEL),y)

 ifeq ($(CONFIG_RISCV_M_MODE)$(CONFIG_SOC_CANAAN),yy)

 KBUILD_IMAGE := $(boot)/loader.bin

diff --git a/arch/riscv/include/asm/vdso.h b/arch/riscv/include/asm/vdso.h

index 1453a2f563bc..d8d003c2b5a3 100644

--- a/arch/riscv/include/asm/vdso.h

+++ b/arch/riscv/include/asm/vdso.h

@@ -9,25 +9,15 @@

 #define _ASM_RISCV_VDSO_H

 #include <linux/types.h>

+#include <generated/vdso-offsets.h>

 #ifndef CONFIG_GENERIC_TIME_VSYSCALL

 struct vdso_data {

 };

 #endif

-/*

- * The VDSO symbols are mapped into Linux so we can just use regular symbol

- * addressing to get their offsets in userspace.  The symbols are mapped at an

- * offset of 0, but since the linker must support setting weak undefined

- * symbols to the absolute address 0 it also happens to support other low

- * addresses even when the code model suggests those low addresses would not

- * otherwise be availiable.

- */

 #define VDSO_SYMBOL(base, name)							\

-({										\

-	extern const char __vdso_##name[];					\

-	(void __user *)((unsigned long)(base) + __vdso_##name);			\

-})

+	(void __user *)((unsigned long)(base) + __vdso_##name##_offset)

 asmlinkage long sys_riscv_flush_icache(uintptr_t, uintptr_t, uintptr_t);

diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile

index 24d936c147cd..f8cb9144a284 100644

--- a/arch/riscv/kernel/vdso/Makefile

+++ b/arch/riscv/kernel/vdso/Makefile

@@ -23,10 +23,10 @@ ifneq ($(c-gettimeofday-y),)

 endif

 # Build rules

-targets := $(obj-vdso) vdso.so vdso.so.dbg vdso.lds vdso-syms.S

+targets := $(obj-vdso) vdso.so vdso.so.dbg vdso.lds

 obj-vdso := $(addprefix $(obj)/, $(obj-vdso))

-obj-y += vdso.o vdso-syms.o

+obj-y += vdso.o

 CPPFLAGS_vdso.lds += -P -C -U$(ARCH)

 # Disable -pg to prevent insert call site

@@ -43,20 +43,22 @@ $(obj)/vdso.o: $(obj)/vdso.so

 # link rule for the .so file, .lds has to be first

 $(obj)/vdso.so.dbg: $(obj)/vdso.lds $(obj-vdso) FORCE

 	$(call if_changed,vdsold)

-LDFLAGS_vdso.so.dbg = -shared -s -soname=linux-vdso.so.1 \

+LDFLAGS_vdso.so.dbg = -shared -S -soname=linux-vdso.so.1 \

 	--build-id=sha1 --hash-style=both --eh-frame-hdr

-# We also create a special relocatable object that should mirror the symbol

-# table and layout of the linked DSO. With ld --just-symbols we can then

-# refer to these symbols in the kernel code rather than hand-coded addresses.

-$(obj)/vdso-syms.S: $(obj)/vdso.so FORCE

-	$(call if_changed,so2s)

-

 # strip rule for the .so file

 $(obj)/%.so: OBJCOPYFLAGS := -S

 $(obj)/%.so: $(obj)/%.so.dbg FORCE

 	$(call if_changed,objcopy)

+# Generate VDSO offsets using helper script

+gen-vdsosym := $(srctree)/$(src)/gen_vdso_offsets.sh

+quiet_cmd_vdsosym = VDSOSYM $@

+	cmd_vdsosym = $(NM) $< | $(gen-vdsosym) | LC_ALL=C sort > $@

+

+include/generated/vdso-offsets.h: $(obj)/vdso.so.dbg FORCE

+	$(call if_changed,vdsosym)

+

 # actual build commands

 # The DSO images are built using a special linker script

 # Make sure only to export the intended __vdso_xxx symbol offsets.

@@ -65,11 +67,6 @@ quiet_cmd_vdsold = VDSOLD  $@

                    $(OBJCOPY) $(patsubst %, -G __vdso_%, $(vdso-syms)) $@.tmp $@ && \

                    rm $@.tmp

-# Extracts symbol offsets from the VDSO, converting them into an assembly file

-# that contains the same symbols at the same offsets.

-quiet_cmd_so2s = SO2S    $@

-      cmd_so2s = $(NM) -D $< | $(srctree)/$(src)/so2s.sh > $@

-

 # install commands for the unstripped file

 quiet_cmd_vdso_install = INSTALL $@

       cmd_vdso_install = cp $(obj)/$@.dbg $(MODLIB)/vdso/$@

diff --git a/arch/riscv/kernel/vdso/gen_vdso_offsets.sh b/arch/riscv/kernel/vdso/gen_vdso_offsets.sh

new file mode 100755

index 000000000000..c2e5613f3495

--- /dev/null

+++ b/arch/riscv/kernel/vdso/gen_vdso_offsets.sh

@@ -0,0 +1,5 @@

+#!/bin/sh

+# SPDX-License-Identifier: GPL-2.0

+

+LC_ALL=C

+sed -n -e 's/^[0]\+\(0[0-9a-fA-F]*\) . \(__vdso_[a-zA-Z0-9_]*\)$/\#define \2_offset\t0x\1/p'

diff --git a/arch/riscv/kernel/vdso/so2s.sh b/arch/riscv/kernel/vdso/so2s.sh

deleted file mode 100755

index e64cb6d9440e..000000000000

--- a/arch/riscv/kernel/vdso/so2s.sh

+++ /dev/null

@@ -1,6 +0,0 @@

-#!/bin/sh

-# SPDX-License-Identifier: GPL-2.0+

-# Copyright 2020 Palmer Dabbelt <palmerdabbelt@google.com>

-

-sed 's!\([0-9a-f]*\) T \([a-z0-9_]*\)\(@@LINUX_4.15\)*!.global \2\n.set \2,0x\1!' \

-| grep '^\.'

-- 

2.26.2