Message-ID: <aPEQJTbADjH9AKUf@debug.ba.rivosinc.com>
Date: Thu, 16 Oct 2025 08:32:53 -0700
From: Deepak Gupta <debug@...osinc.com>
To: Zong Li <zong.li@...ive.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
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Subject: Re: [PATCH v20 24/28] arch/riscv: dual vdso creation logic and
 select vdso based on hw

On Thu, Oct 16, 2025 at 04:32:08PM +0800, Zong Li wrote:
>On Tue, Oct 14, 2025 at 5:57 AM Deepak Gupta <debug@...osinc.com> wrote:
>>
>> Shadow stack instructions are taken from zimop (mandated on RVA23).
>> Any hardware prior to RVA23 profile will fault on shado stack instruction.
>
>I notice that there is a typo for shado"w" stack instruction.

Aah yes. Sorry about it and thanks.
Again upto Paul, if he wants me to send another. I'll do that.

-Deepak

>
>> 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).
>>
>> Signed-off-by: Deepak Gupta <debug@...osinc.com>
>> ---
>>  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
>>
>>
>> _______________________________________________
>> linux-riscv mailing list
>> linux-riscv@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-riscv

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