[PATCH v12 24/28] arch/riscv: compile vdso with landing pad

Deepak Gupta
2025-03-14T21:40:31Z

From: Jim Shu <jim.shu@sifive.com>

user mode tasks compiled with zicfilp may call indirectly into vdso (like
hwprobe indirect calls). Add landing pad compile support in vdso. vdso
with landing pad in it will be nop for tasks which have not enabled
landing pad.
This patch allows to run user mode tasks with cfi eanbled and do no harm.

Future work can be done on this to do below
- labeled landing pad on vdso functions (whenever labeling support shows
up in gnu-toolchain)
- emit shadow stack instructions only in vdso compiled objects as part of
kernel compile.

Signed-off-by: Jim Shu <jim.shu@sifive.com>
Reviewed-by: Zong Li <zong.li@sifive.com>
Signed-off-by: Deepak Gupta <debug@rivosinc.com>
---
arch/riscv/Makefile | 5 +++-
arch/riscv/include/asm/assembler.h | 44 +++++++++++++++++++++++++++++++++++
arch/riscv/kernel/vdso/Makefile | 12 ++++++++++
arch/riscv/kernel/vdso/flush_icache.S | 4 ++++
arch/riscv/kernel/vdso/getcpu.S | 4 ++++
arch/riscv/kernel/vdso/rt_sigreturn.S | 4 ++++
arch/riscv/kernel/vdso/sys_hwprobe.S | 4 ++++
7 files changed, 76 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 13fbc0f94238..eca94246cda6 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -88,9 +88,12 @@ riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZACAS) := $(riscv-march-y)_zacas
# Check if the toolchain supports Zabha
riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZABHA) := $(riscv-march-y)_zabha

+KBUILD_BASE_ISA = -march=$(shell echo $(riscv-march-y) | sed -E 's/(rv32ima|rv64ima)fd([^v_]*)v?/\1\2/')
+export KBUILD_BASE_ISA
+
# Remove F,D,V from isa string for all. Keep extensions between "fd" and "v" by
# matching non-v and non-multi-letter extensions out with the filter ([^v_]*)
-KBUILD_CFLAGS += -march=$(shell echo $(riscv-march-y) | sed -E 's/(rv32ima|rv64ima)fd([^v_]*)v?/\1\2/')
+KBUILD_CFLAGS += $(KBUILD_BASE_ISA)

KBUILD_AFLAGS += -march=$(riscv-march-y)

diff --git a/arch/riscv/include/asm/assembler.h b/arch/riscv/include/asm/assembler.h
index 44b1457d3e95..a058ea5e9c58 100644
--- a/arch/riscv/include/asm/assembler.h
+++ b/arch/riscv/include/asm/assembler.h
@@ -80,3 +80,47 @@
.endm

#endif /* __ASM_ASSEMBLER_H */
+
+#if defined(CONFIG_RISCV_USER_CFI) && (__riscv_xlen == 64)
+.macro vdso_lpad
+lpad 0
+.endm
+#else
+.macro vdso_lpad
+.endm
+#endif
+
+/*
+ * This macro emits a program property note section identifying
+ * architecture features which require special handling, mainly for
+ * use in assembly files included in the VDSO.
+ */
+#define NT_GNU_PROPERTY_TYPE_0 5
+#define GNU_PROPERTY_RISCV_FEATURE_1_AND 0xc0000000
+
+#define GNU_PROPERTY_RISCV_FEATURE_1_ZICFILP (1U << 0)
+#define GNU_PROPERTY_RISCV_FEATURE_1_ZICFISS (1U << 1)
+
+#if defined(CONFIG_RISCV_USER_CFI) && (__riscv_xlen == 64)
+#define GNU_PROPERTY_RISCV_FEATURE_1_DEFAULT \
+ (GNU_PROPERTY_RISCV_FEATURE_1_ZICFILP)
+#endif
+
+#ifdef GNU_PROPERTY_RISCV_FEATURE_1_DEFAULT
+.macro emit_riscv_feature_1_and, feat = GNU_PROPERTY_RISCV_FEATURE_1_DEFAULT
+ .pushsection .note.gnu.property, "a"
+ .p2align 3
+ .word 4
+ .word 16
+ .word NT_GNU_PROPERTY_TYPE_0
+ .asciz "GNU"
+ .word GNU_PROPERTY_RISCV_FEATURE_1_AND
+ .word 4
+ .word \feat
+ .word 0
+ .popsection
+.endm
+#else
+.macro emit_riscv_feature_1_and, feat = 0
+.endm
+#endif
diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
index 9a1b555e8733..daa10c2b0dd1 100644
--- a/arch/riscv/kernel/vdso/Makefile
+++ b/arch/riscv/kernel/vdso/Makefile
@@ -13,12 +13,18 @@ vdso-syms += flush_icache
vdso-syms += hwprobe
vdso-syms += sys_hwprobe

+ifdef CONFIG_RISCV_USER_CFI
+LPAD_MARCH = _zicfilp
+endif
+
# Files to link into the vdso
obj-vdso = $(patsubst %, %.o, $(vdso-syms)) note.o

ccflags-y := -fno-stack-protector
ccflags-y += -DDISABLE_BRANCH_PROFILING
ccflags-y += -fno-builtin
+ccflags-y += $(KBUILD_BASE_ISA)$(LPAD_MARCH)
+asflags-y += $(KBUILD_BASE_ISA)$(LPAD_MARCH)

ifneq ($(c-gettimeofday-y),)
CFLAGS_vgettimeofday.o += -fPIC -include $(c-gettimeofday-y)
@@ -40,6 +46,12 @@ endif
CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS)
CFLAGS_REMOVE_hwprobe.o = $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS)

+# Disable profiling and instrumentation for VDSO code
+GCOV_PROFILE := n
+KCOV_INSTRUMENT := n
+KASAN_SANITIZE := n
+UBSAN_SANITIZE := n
+
# Force dependency
$(obj)/vdso.o: $(obj)/vdso.so

diff --git a/arch/riscv/kernel/vdso/flush_icache.S b/arch/riscv/kernel/vdso/flush_icache.S
index 8f884227e8bc..e4c56970905e 100644
--- a/arch/riscv/kernel/vdso/flush_icache.S
+++ b/arch/riscv/kernel/vdso/flush_icache.S
@@ -5,11 +5,13 @@

#include <linux/linkage.h>
#include <asm/unistd.h>
+#include <asm/assembler.h>

.text
/* int __vdso_flush_icache(void *start, void *end, unsigned long flags); */
SYM_FUNC_START(__vdso_flush_icache)
.cfi_startproc
+ vdso_lpad
#ifdef CONFIG_SMP
li a7, __NR_riscv_flush_icache
ecall
@@ -20,3 +22,5 @@ SYM_FUNC_START(__vdso_flush_icache)
ret
.cfi_endproc
SYM_FUNC_END(__vdso_flush_icache)
+
+emit_riscv_feature_1_and
diff --git a/arch/riscv/kernel/vdso/getcpu.S b/arch/riscv/kernel/vdso/getcpu.S
index 9c1bd531907f..5c1ecc4e1465 100644
--- a/arch/riscv/kernel/vdso/getcpu.S
+++ b/arch/riscv/kernel/vdso/getcpu.S
@@ -5,14 +5,18 @@

#include <linux/linkage.h>
#include <asm/unistd.h>
+#include <asm/assembler.h>

.text
/* int __vdso_getcpu(unsigned *cpu, unsigned *node, void *unused); */
SYM_FUNC_START(__vdso_getcpu)
.cfi_startproc
+ vdso_lpad
/* For now, just do the syscall. */
li a7, __NR_getcpu
ecall
ret
.cfi_endproc
SYM_FUNC_END(__vdso_getcpu)
+
+emit_riscv_feature_1_and
diff --git a/arch/riscv/kernel/vdso/rt_sigreturn.S b/arch/riscv/kernel/vdso/rt_sigreturn.S
index 3dc022aa8931..e82987dc3739 100644
--- a/arch/riscv/kernel/vdso/rt_sigreturn.S
+++ b/arch/riscv/kernel/vdso/rt_sigreturn.S
@@ -5,12 +5,16 @@

#include <linux/linkage.h>
#include <asm/unistd.h>
+#include <asm/assembler.h>

.text
SYM_FUNC_START(__vdso_rt_sigreturn)
.cfi_startproc
.cfi_signal_frame
+ vdso_lpad
li a7, __NR_rt_sigreturn
ecall
.cfi_endproc
SYM_FUNC_END(__vdso_rt_sigreturn)
+
+emit_riscv_feature_1_and
diff --git a/arch/riscv/kernel/vdso/sys_hwprobe.S b/arch/riscv/kernel/vdso/sys_hwprobe.S
index 77e57f830521..f1694451a60c 100644
--- a/arch/riscv/kernel/vdso/sys_hwprobe.S
+++ b/arch/riscv/kernel/vdso/sys_hwprobe.S
@@ -3,13 +3,17 @@

#include <linux/linkage.h>
#include <asm/unistd.h>
+#include <asm/assembler.h>

.text
SYM_FUNC_START(riscv_hwprobe)
.cfi_startproc
+ vdso_lpad
li a7, __NR_riscv_hwprobe
ecall
ret

.cfi_endproc
SYM_FUNC_END(riscv_hwprobe)
+
+emit_riscv_feature_1_and

--
2.34.1