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 devnull+debug.rivosinc.com@kernel.org 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:

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.

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.

I have it working on my end with latest upstream opensbi (no hacks, same compiler)

""" $ git log commit 38a6106b1099646f25657bba53cefb80886721a7 (HEAD -> master, origin/master, origin/HEAD) Author: Benoît Monin benoit.monin@bootlin.com Date: Mon Oct 27 14:12:17 2025 +0100

lib: utils/ipi: mswi: add MIPS P8700 compatible .... """

I am surprised that change of compiler on opensbi changed errorcode for userspace in your setup. That's quite bizarre.

Output from cfitests (with toolchain that's on docker. I didn't compile from cfi-dev branch).

# /mnt/cfitests TAP version 13 # Starting risc-v tests # Landing pad and shadow stack are enabled for binary # cfi_ptrace_test, ptrace test succeeded # Executing RISC-V shadow stack self tests 1..5 # Exercising shadow stack fork test # Parent pid 133 and child pid 135 # dummy calls for sspush and sspopchk in context of parent # Spewing out shadow stack ptr: 7fffbf4a9fb8 This is to ensure shadow stack is indeed enabled and working # Waiting on child to finish # dummy calls for sspush and sspopchk in context of child # Spewing out shadow stack ptr: 7fffbf4a9fb8 This is to ensure shadow stack is indeed enabled and working ok 1 shstk fork test # Exercising shadow stack map test ok 2 map shadow stack syscall # Exercising shadow stack gup tests ok 3 shadow stack gup tests # Exercising shadow stack signal test ok 4 shadow stack signal tests # Exercising shadow stack protection test (WPT) ok 5 memory protections of shadow stack memory # Totals: pass:5 fail:0 xfail:0 xpass:0 skip:0 error:0 #

Is there a place where I can grab your kselftest `cfitests` binary?

Only difference I can see is that `cfitests` in my case is not statically compiled

""" $ riscv64-unknown-linux-gnu-readelf -d /scratch/debug/sources/spectacles/cfitests | grep NEEDED 0x0000000000000001 (NEEDED) Shared library: [libc.so.6]

"""

Cheers,

Joel

...

How to test this series

Toolchain

$ git clone git@github.com: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 git@github.com: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