riscv: dual vdso creation logic and select vdso based on hw

Deepak Gupta Fri, 17 Oct 2025 18:01:38 -0700

Hi Charles,


On Wed, Oct 15, 2025 at 04:36:11PM -0400, Charles Mirabile wrote:

Hi Deepak -

On Mon, Oct 13, 2025 at 02:56:16PM -0700, Deepak Gupta wrote:

Shadow stack instructions are taken from zimop (mandated on RVA23).
Any hardware prior to RVA23 profile will fault on shado stack instruction.
Any userspace with shadow stack instruction in it will fault on such
hardware. Thus such userspace can't be brought onto such a hardware.

It's not known how userspace will respond to such binary fragmentation.
However in order to keep kernel portable across such different hardware,
`arch/riscv/kernel/vdso_cfi` is created which has logic (Makefile) to
compile `arch/riscv/kernel/vdso` sources with cfi flags and then changes
in `arch/riscv/kernel/vdso.c` for selecting appropriate vdso depending
on whether underlying hardware(cpu) implements zimop extension. Offset
of vdso symbols will change due to having two different vdso binaries,
there is added logic to include new generated vdso offset header and
dynamically select offset (like for rt_sigreturn).


This looks great. As kernel test robot highlighted, the code doesn't build
when the config is off, but I was able to fix it with the attached patch.


Yes sorry about that. Locally include/generated had both files and that's how
I missed it.


Assuming that these changes or equivalent are folded in, you have my:


Yes v21 changes are equivalent to what you proposed.

Acked-by: Charles Mirabile <[email protected]>


If I send another version due to some other issue, I'll collect your tag.

Else
Paul,

Can you apply the tag when you take it in.

-Deepak


As merely a user whose previous concerns have been addressed, I am not
sure what that is worth, but I appreciate your effort on this.


Thanks.


Signed-off-by: Deepak Gupta <[email protected]>
---
 arch/riscv/Makefile                        |  3 +++
 arch/riscv/include/asm/vdso.h              |  7 ++++++-
 arch/riscv/kernel/Makefile                 |  1 +
 arch/riscv/kernel/vdso.c                   |  7 +++++++
 arch/riscv/kernel/vdso/Makefile            | 29 ++++++++++++++++++++---------
 arch/riscv/kernel/vdso/gen_vdso_offsets.sh |  4 +++-
 arch/riscv/kernel/vdso_cfi/Makefile        | 25 +++++++++++++++++++++++++
 arch/riscv/kernel/vdso_cfi/vdso-cfi.S      | 11 +++++++++++
 8 files changed, 76 insertions(+), 11 deletions(-)

diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index f60c2de0ca08..b74b63da16a7 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -176,6 +176,8 @@ ifeq ($(CONFIG_MMU),y)
 prepare: vdso_prepare
 vdso_prepare: prepare0
        $(Q)$(MAKE) $(build)=arch/riscv/kernel/vdso 
include/generated/vdso-offsets.h
+       $(if $(CONFIG_RISCV_USER_CFI),$(Q)$(MAKE) \
+               $(build)=arch/riscv/kernel/vdso_cfi 
include/generated/vdso-cfi-offsets.h)
        $(if $(CONFIG_COMPAT),$(Q)$(MAKE) \
                $(build)=arch/riscv/kernel/compat_vdso 
include/generated/compat_vdso-offsets.h)

@@ -183,6 +185,7 @@ endif
 endif

 vdso-install-y                 += arch/riscv/kernel/vdso/vdso.so.dbg
+vdso-install-$(CONFIG_RISCV_USER_CFI)  += 
arch/riscv/kernel/vdso_cfi/vdso-cfi.so.dbg
 vdso-install-$(CONFIG_COMPAT)  += 
arch/riscv/kernel/compat_vdso/compat_vdso.so.dbg

 BOOT_TARGETS := Image Image.gz Image.bz2 Image.lz4 Image.lzma Image.lzo 
Image.zst Image.xz loader loader.bin xipImage vmlinuz.efi
diff --git a/arch/riscv/include/asm/vdso.h b/arch/riscv/include/asm/vdso.h
index f80357fe24d1..3fc8f72b8bfb 100644
--- a/arch/riscv/include/asm/vdso.h
+++ b/arch/riscv/include/asm/vdso.h
@@ -18,9 +18,13 @@

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

 #define VDSO_SYMBOL(base, name)                                                
        \
-       (void __user *)((unsigned long)(base) + __vdso_##name##_offset)
+       ((IS_ENABLED(CONFIG_RISCV_USER_CFI) &&                                  
\
+         riscv_has_extension_unlikely(RISCV_ISA_EXT_ZIMOP)) ?                  
\
+         (void __user *)((unsigned long)(base) + __vdso_##name##_cfi_offset) : 
\
+         (void __user *)((unsigned long)(base) + __vdso_##name##_offset))

 #ifdef CONFIG_COMPAT
 #include <generated/compat_vdso-offsets.h>
@@ -33,6 +37,7 @@ extern char compat_vdso_start[], compat_vdso_end[];
 #endif /* CONFIG_COMPAT */

 extern char vdso_start[], vdso_end[];
+extern char vdso_cfi_start[], vdso_cfi_end[];

 #endif /* !__ASSEMBLER__ */

diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 2d0e0dcedbd3..9026400cba10 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -72,6 +72,7 @@ obj-y += vendor_extensions/
 obj-y  += probes/
 obj-y  += tests/
 obj-$(CONFIG_MMU) += vdso.o vdso/
+obj-$(CONFIG_RISCV_USER_CFI) += vdso_cfi/

 obj-$(CONFIG_RISCV_MISALIGNED) += traps_misaligned.o
 obj-$(CONFIG_RISCV_MISALIGNED) += unaligned_access_speed.o
diff --git a/arch/riscv/kernel/vdso.c b/arch/riscv/kernel/vdso.c
index 3a8e038b10a2..bf080e519101 100644
--- a/arch/riscv/kernel/vdso.c
+++ b/arch/riscv/kernel/vdso.c
@@ -98,6 +98,13 @@ static struct __vdso_info compat_vdso_info __ro_after_init = 
{

 static int __init vdso_init(void)
 {
+       /* Hart implements zimop, expose cfi compiled vdso */
+       if (IS_ENABLED(CONFIG_RISCV_USER_CFI) &&
+               riscv_has_extension_unlikely(RISCV_ISA_EXT_ZIMOP)) {
+               vdso_info.vdso_code_start = vdso_cfi_start;
+               vdso_info.vdso_code_end = vdso_cfi_end;
+       }
+
        __vdso_init(&vdso_info);
 #ifdef CONFIG_COMPAT
        __vdso_init(&compat_vdso_info);
diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
index 272f1d837a80..a842dc034571 100644
--- a/arch/riscv/kernel/vdso/Makefile
+++ b/arch/riscv/kernel/vdso/Makefile
@@ -20,6 +20,10 @@ endif
 ifdef VDSO_CFI_BUILD
 CFI_MARCH = _zicfilp_zicfiss
 CFI_FULL = -fcf-protection=full
+CFI_SUFFIX = -cfi
+OFFSET_SUFFIX = _cfi
+ccflags-y += -DVDSO_CFI=1
+asflags-y += -DVDSO_CFI=1
 endif

 # Files to link into the vdso
@@ -48,13 +52,20 @@ endif
 CFLAGS_hwprobe.o += -fPIC

 # Build rules
-targets := $(obj-vdso) vdso.so vdso.so.dbg vdso.lds
+vdso_offsets := vdso$(if $(VDSO_CFI_BUILD),$(CFI_SUFFIX),)-offsets.h
+vdso_o := vdso$(if $(VDSO_CFI_BUILD),$(CFI_SUFFIX),).o
+vdso_so := vdso$(if $(VDSO_CFI_BUILD),$(CFI_SUFFIX),).so
+vdso_so_dbg := vdso$(if $(VDSO_CFI_BUILD),$(CFI_SUFFIX),).so.dbg
+vdso_lds := vdso.lds
+
+targets := $(obj-vdso) $(vdso_so) $(vdso_so_dbg) $(vdso_lds)
+
 obj-vdso := $(addprefix $(obj)/, $(obj-vdso))

-obj-y += vdso.o
-CPPFLAGS_vdso.lds += -P -C -U$(ARCH)
+obj-y += vdso$(if $(VDSO_CFI_BUILD),$(CFI_SUFFIX),).o
+CPPFLAGS_$(vdso_lds) += -P -C -U$(ARCH)
 ifneq ($(filter vgettimeofday, $(vdso-syms)),)
-CPPFLAGS_vdso.lds += -DHAS_VGETTIMEOFDAY
+CPPFLAGS_$(vdso_lds) += -DHAS_VGETTIMEOFDAY
 endif

 # Disable -pg to prevent insert call site
@@ -63,12 +74,12 @@ CFLAGS_REMOVE_getrandom.o = $(CC_FLAGS_FTRACE) 
$(CC_FLAGS_SCS)
 CFLAGS_REMOVE_hwprobe.o = $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS)

 # Force dependency
-$(obj)/vdso.o: $(obj)/vdso.so
+$(obj)/$(vdso_o): $(obj)/$(vdso_so)

 # link rule for the .so file, .lds has to be first
-$(obj)/vdso.so.dbg: $(obj)/vdso.lds $(obj-vdso) FORCE
+$(obj)/$(vdso_so_dbg): $(obj)/$(vdso_lds) $(obj-vdso) FORCE
        $(call if_changed,vdsold_and_check)
-LDFLAGS_vdso.so.dbg = -shared -soname=linux-vdso.so.1 \
+LDFLAGS_$(vdso_so_dbg) = -shared -soname=linux-vdso.so.1 \
        --build-id=sha1 --eh-frame-hdr

 # strip rule for the .so file
@@ -79,9 +90,9 @@ $(obj)/%.so: $(obj)/%.so.dbg FORCE
 # Generate VDSO offsets using helper script
 gen-vdsosym := $(src)/gen_vdso_offsets.sh
 quiet_cmd_vdsosym = VDSOSYM $@
-       cmd_vdsosym = $(NM) $< | $(gen-vdsosym) | LC_ALL=C sort > $@
+       cmd_vdsosym = $(NM) $< | $(gen-vdsosym) $(OFFSET_SUFFIX) | LC_ALL=C sort 
> $@

-include/generated/vdso-offsets.h: $(obj)/vdso.so.dbg FORCE
+include/generated/$(vdso_offsets): $(obj)/$(vdso_so_dbg) FORCE
        $(call if_changed,vdsosym)

 # actual build commands
diff --git a/arch/riscv/kernel/vdso/gen_vdso_offsets.sh 
b/arch/riscv/kernel/vdso/gen_vdso_offsets.sh
index c2e5613f3495..bd5d5afaaa14 100755
--- a/arch/riscv/kernel/vdso/gen_vdso_offsets.sh
+++ b/arch/riscv/kernel/vdso/gen_vdso_offsets.sh
@@ -2,4 +2,6 @@
 # SPDX-License-Identifier: GPL-2.0

 LC_ALL=C
-sed -n -e 's/^[0]\+\(0[0-9a-fA-F]*\) . \(__vdso_[a-zA-Z0-9_]*\)$/\#define 
\2_offset\t0x\1/p'
+SUFFIX=${1:-""}
+sed -n -e \
+'s/^[0]\+\(0[0-9a-fA-F]*\) . \(__vdso_[a-zA-Z0-9_]*\)$/\#define 
\2'$SUFFIX'_offset\t0x\1/p'
diff --git a/arch/riscv/kernel/vdso_cfi/Makefile 
b/arch/riscv/kernel/vdso_cfi/Makefile
new file mode 100644
index 000000000000..8ebd190782b0
--- /dev/null
+++ b/arch/riscv/kernel/vdso_cfi/Makefile
@@ -0,0 +1,25 @@
+# SPDX-License-Identifier: GPL-2.0-only
+# RISC-V VDSO CFI Makefile
+# This Makefile builds the VDSO with CFI support when CONFIG_RISCV_USER_CFI is 
enabled
+
+# setting VDSO_CFI_BUILD triggers build for vdso differently
+VDSO_CFI_BUILD := 1
+
+# Set the source directory to the main vdso directory
+src := $(srctree)/arch/riscv/kernel/vdso
+
+# Copy all .S and .c files from vdso directory to vdso_cfi object build 
directory
+vdso_c_sources := $(wildcard $(src)/*.c)
+vdso_S_sources := $(wildcard $(src)/*.S)
+vdso_c_objects := $(addprefix $(obj)/, $(notdir $(vdso_c_sources)))
+vdso_S_objects := $(addprefix $(obj)/, $(notdir $(vdso_S_sources)))
+
+$(vdso_S_objects): $(obj)/%.S: $(src)/%.S
+       $(Q)cp $< $@
+
+$(vdso_c_objects): $(obj)/%.c: $(src)/%.c
+       $(Q)cp $< $@
+
+# Include the main VDSO Makefile which contains all the build rules and sources
+# The VDSO_CFI_BUILD variable will be passed to it to enable CFI compilation
+include $(src)/Makefile
diff --git a/arch/riscv/kernel/vdso_cfi/vdso-cfi.S 
b/arch/riscv/kernel/vdso_cfi/vdso-cfi.S
new file mode 100644
index 000000000000..d426f6accb35
--- /dev/null
+++ b/arch/riscv/kernel/vdso_cfi/vdso-cfi.S
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2025 Rivos, Inc
+ */
+
+#define        vdso_start      vdso_cfi_start
+#define        vdso_end        vdso_cfi_end
+
+#define __VDSO_PATH "arch/riscv/kernel/vdso_cfi/vdso-cfi.so"
+
+#include "../vdso/vdso.S"

--
2.43.0


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---
diff --git a/arch/riscv/include/asm/vdso.h b/arch/riscv/include/asm/vdso.h
index 3fc8f72b8bfb..9cfbb390270f 100644
--- a/arch/riscv/include/asm/vdso.h
+++ b/arch/riscv/include/asm/vdso.h
@@ -18,13 +18,21 @@

#ifndef __ASSEMBLER__
#include <generated/vdso-offsets.h>
+#if IS_ENABLED(CONFIG_RISCV_USER_CFI)
+
#include <generated/vdso-cfi-offsets.h>

#define VDSO_SYMBOL(base, name)                                                 
\
-       ((IS_ENABLED(CONFIG_RISCV_USER_CFI) &&                                  
\
-         riscv_has_extension_unlikely(RISCV_ISA_EXT_ZIMOP)) ?                  
\
-         (void __user *)((unsigned long)(base) + __vdso_##name##_cfi_offset) : 
\
-         (void __user *)((unsigned long)(base) + __vdso_##name##_offset))
+       (riscv_has_extension_unlikely(RISCV_ISA_EXT_ZIMOP)) ?                   
\
+        (void __user *)((unsigned long)(base) + __vdso_##name##_cfi_offset) :  
\
+        (void __user *)((unsigned long)(base) + __vdso_##name##_offset)
+
+#else /* !CONFIG_RISCV_USER_CFI */
+
+#define VDSO_SYMBOL(base, name)                                                
        \
+       (void __user *)((unsigned long)(base) + __vdso_##name##_offset)
+
+#endif /* CONFIG_RISCV_USER_CFI */

#ifdef CONFIG_COMPAT
#include <generated/compat_vdso-offsets.h>

Re: [PATCH v20 24/28] arch/riscv: dual vdso creation logic and select vdso based on hw

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