Hi Joel,
Thanks a lot for testing it out.
Comments inline.
On Tue, Nov 04, 2025 at 05:34:11PM +1030, Joel Stanley wrote:
Hello Deepak,
On Fri, 24 Oct 2025 at 03:31, Deepak Gupta via B4 Relay
<[email protected]> wrote:
v22: fixing build error due to -march=zicfiss being picked in gcc-13 and above
but not actually doing any codegen or recognizing instruction for zicfiss.
Change in v22 makes dependence on `-fcf-protection=full` compiler flag to
ensure that toolchain has support and then only CONFIG_RISCV_USER_CFI will be
visible in menuconfig.
Following our discussion at the riscv summit I spent some time with
this patch set with the goal of giving a test run on emulation. I only
got as far as qemu, as I couldn't get the selftests passing there.
I had trouble running the podman container so I built a toolchain
using the riscv-gnu-toolchain branch (cfi-dev, d19f3009f6c2) you
pointed to.
The opensbi branch was a bit old and wouldn't build with GCC 15, so I
tried to rebase and noticed the patches were already upstream. Have
you tested using v1.7 (or newer) there? Is there something I missed,
do we need more patches on upstream opensbi?
I booted it in qemu 10.1.2 with the zicfi extensions both on and off.
qemu-system-riscv64 -M virt,aia=aplic-imsic,aia-guests=5 \
-cpu rv64,zicfilp=true,zicfiss=true,zimop=true,zcmop=true
-smp 8 -nographic -bios fw_dynamic.elf
-m 1024M -kernel arch/riscv/boot/Image \
-initrd selftests/selftests.cpio \
-append 'init=mini-init command="cfitests"'
My results:
no zicfi, no z*mop (crash, as expected):
-------------------------------------------------
Running command: cfitests
system_opcode_insn: Invalid opcode for CSR read/write instruction[
0.462709] cfitests[85]: unhandled signal 4 code 0x1 at
0x0000000000011c44 in cfitests[1c44,10000+6d000]
[ 0.463141] CPU: 4 UID: 0 PID: 85 Comm: cfitests Not tainted
6.18.0-rc3-tt-defconfig-jms-00090-g6e2297f1edbc #93 NONE
[ 0.463338] Hardware name: riscv-virtio,qemu (DT)
[ 0.463573] epc : 0000000000011c44 ra : 00000000000104e0 sp :
00007fffebd0ddb0
...
[ 0.465177] status: 0000000200004020 badaddr: 00000000ce104073
cause: 0000000000000002
[ 0.465410] Code: 0893 05d0 4501 0073 0000 b7f5 4501 b7f9 0017 0000
(4073) ce10
no zicfi, z*mop (failed to start, as expected):
-----------------------------------------------------------
Running command: cfitests
TAP version 13
# Starting risc-v CFI tests
Bail out! Get landing pad status failed with -22
zicfi, z*mop (failed to start, unexpected):
-------------------------------------------------------
Running command: cfitests
TAP version 13
# Starting risc-v CFI tests
Bail out! Get landing pad status failed with -22
I went digging to see why the zicfi enabled kernel failed. The
userspace binary was built with CFI:
$ riscv64-unknown-linux-gnu-readelf -n selftests/cfitests
Displaying notes found in: .note.gnu.property
Owner Data size Description
GNU 0x00000010 NT_GNU_PROPERTY_TYPE_0
Properties: RISC-V AND feature: CFI_LP_UNLABELED, CFI_SS
I then tested your opensbi tree with some hacks to get it built with a
newer compiler. This produced different results, which was unexpected:
Opensbi doesn't need to be built with new compiler. All it needs do are
reflect MPELP bit back to S-mode (if its taking a trap and then reflecting
back to S-mode) and ofcourse have SSE support. Both of these are upstream
in opensbi.
I'll test with upstream opensbi, test and report back.
Running command: cfitests
TAP version 13
# Starting risc-v CFI tests
Bail out! Landing pad is not enabled, should be enabled via glibc
# Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0
The selftest binary and the little toy init that starts it are both
statically linked and built against the toolchain's glibc, so I would
expect this to work.
$ riscv64-unknown-linux-gnu-readelf -n sifive-cfi-build/sysroot/usr/lib/libc.a
File: sifive-cfi-build/sysroot/usr/lib/libc.a(init-first.o)
Displaying notes found in: .note.gnu.property
Owner Data size Description
GNU 0x00000010 NT_GNU_PROPERTY_TYPE_0
Properties: RISC-V AND feature: CFI_LP_UNLABELED, CFI_SS
The kernel seems to have detected that CFI is available and is built with it:
$ grep CFI .config
CONFIG_RISCV_USER_CFI=y
CONFIG_ARCH_SUPPORTS_CFI=y
I did notice the func-sig-dev gcc branch is a few commits ahead of
what the sifive riscv-gnu-toolchain points to.
Most likely PRCTL_* is not updated in cfi-dev branch? I'll take a look.
I had to context switch to some other tasks at this point. I wanted to
do some more digging to work out what was wrong, but I haven't found
time, so here are my notes in the hope that they are useful. I'll let
you know if I discover anything further.
Thanks once again.
Cheers,
Joel
How to test this series
=======================
Toolchain
---------
$ git clone [email protected]:sifive/riscv-gnu-toolchain.git -b cfi-dev
$ riscv-gnu-toolchain/configure --prefix=<path-to-where-to-build>
--with-arch=rv64gc_zicfilp_zicfiss --enable-linux --disable-gdb
--with-extra-multilib-test="rv64gc_zicfilp_zicfiss-lp64d:-static"
$ make -j$(nproc)
Qemu
----
Get the lastest qemu
$ cd qemu
$ mkdir build
$ cd build
$ ../configure --target-list=riscv64-softmmu
$ make -j$(nproc)
Opensbi
-------
$ git clone [email protected]:deepak0414/opensbi.git -b v6_cfi_spec_split_opensbi
$ make CROSS_COMPILE=<your riscv toolchain> -j$(nproc) PLATFORM=generic
Linux
-----
Running defconfig is fine. CFI is enabled by default if the toolchain
supports it.
$ make ARCH=riscv
CROSS_COMPILE=<path-to-cfi-riscv-gnu-toolchain>/build/bin/riscv64-unknown-linux-gnu-
-j$(nproc) defconfig
$ make ARCH=riscv
CROSS_COMPILE=<path-to-cfi-riscv-gnu-toolchain>/build/bin/riscv64-unknown-linux-gnu-
-j$(nproc)
Running
-------
Modify your qemu command to have:
-bios <path-to-cfi-opensbi>/build/platform/generic/firmware/fw_dynamic.bin
-cpu rv64,zicfilp=true,zicfiss=true,zimop=true,zcmop=true
