Re: [PATCH RFC] arch/riscv: add proc status (proc/<pid>/status)

[Heinrich Schuchardt <heinrich.schuchardt@canonical.com>]

On 10/20/25 20:18, Deepak Gupta wrote:
> x86 has proc/<pid>/status to see various runtime characteristics
> of running task. Implement same for riscv. This patch implements
> status for shadow stack and landing pad state.
> 
> Signed-off-by: Deepak Gupta <debug@rivosinc.com>
> ---
> This is just a one patch but sending it as RFC with cover letter to seek
> feedback. x86 has `arch_proc_pid_thread_features` to enumerate status of
> arch thread specific features on runtime. This can be done using prctl
> as well but from quick/script perspective `cat /proc/<pid>/status` is more
> desirable. In this patch, simply `arch_proc_pid_thread_features` is implemented
> for riscv which queries shadow stack and landing pad state and reports back.
> Thus it is dependent on riscv user cfi enabling series.

Hello Deepak,

This looks like a valuable addition.

Shouldn't architecture specific fields be in
/proc/<pid>/arch_status and not in /proc/<pid>/status?

Please, add a documentation patch adding the RISC-V specific fields to
"3.12  /proc/<pid>/arch_status - Task architecture specific information"
in Documentation/filesystems/proc.rst.

Should you stick to /proc/*/status, please, add the documentation to 
Documentation/arch/riscv/.

> 
> If this patch itself is self-standing and good enough, I can roll this patch
> as part of riscv user cfi enabling series.
> 
> OR
> 
> If there is ask for other riscv thread specific features that could be
> enumerated in similar fashion, we will need it to be done as separate series
> (with `thread_features` added to `thread_info`)
> 
> Example output below.
> 
> Name:   cat
> Umask:  0022
> State:  R (running)
> Tgid:   133
> Ngid:   0
> Pid:    133
> PPid:   129
> TracerPid:      0
> Uid:    0       0       0       0
> Gid:    0       0       0       0
> FDSize: 256
> Groups: 0 10
> NStgid: 133
> NSpid:  133
> NSpgid: 133
> NSsid:  129
> Kthread:        0
> VmPeak:    10788 kB
> VmSize:    10788 kB
> VmLck:         0 kB
> VmPin:         0 kB
> VmHWM:      1400 kB
> VmRSS:      1400 kB
> RssAnon:             116 kB
> RssFile:            1284 kB
> RssShmem:              0 kB
> VmData:       92 kB
> VmStk:      8324 kB
> VmExe:         4 kB
> VmLib:      2312 kB
> VmPTE:        40 kB
> VmSwap:        0 kB
> HugetlbPages:          0 kB
> CoreDumping:    0
> THP_enabled:    0
> untag_mask:     0xffffffffffffffff
> Threads:        1
> SigQ:   0/31771
> SigPnd: 0000000000000000
> ShdPnd: 0000000000000000
> SigBlk: 0000000000000000
> SigIgn: 0000000000000000
> SigCgt: 0000000000000000
> CapInh: 0000000000000000
> CapPrm: 000001ffffffffff
> CapEff: 000001ffffffffff
> CapBnd: 000001ffffffffff
> CapAmb: 0000000000000000
> NoNewPrivs:     0
> Seccomp:        0
> Seccomp_filters:        0
> Speculation_Store_Bypass:       unknown
> SpeculationIndirectBranch:      unsupported
> Cpus_allowed:   3
> Cpus_allowed_list:      0-1
> Mems_allowed:   1
> Mems_allowed_list:      0
> voluntary_ctxt_switches:        0
> nonvoluntary_ctxt_switches:     3
> riscv_thread_features:  shstk_enabled lpad_enabled
> riscv_thread_features_locked:   shstk_unlocked lpad_unlocked
> ---
>   arch/riscv/kernel/Makefile     |  1 +
>   arch/riscv/kernel/cpu/Makefile |  1 +
>   arch/riscv/kernel/cpu/proc.c   | 28 ++++++++++++++++++++++++++++
>   3 files changed, 30 insertions(+)
> 
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index f60fce69b725..b32c11667d81 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -71,6 +71,7 @@ obj-y	+= vendor_extensions.o
>   obj-y	+= vendor_extensions/
>   obj-y	+= probes/
>   obj-y	+= tests/
> +obj-y	+= cpu/
>   obj-$(CONFIG_MMU) += vdso.o vdso/
>   
>   obj-$(CONFIG_RISCV_MISALIGNED)	+= traps_misaligned.o
> diff --git a/arch/riscv/kernel/cpu/Makefile b/arch/riscv/kernel/cpu/Makefile
> new file mode 100644
> index 000000000000..2b474fb49afe
> --- /dev/null
> +++ b/arch/riscv/kernel/cpu/Makefile
> @@ -0,0 +1 @@
> +obj-$(CONFIG_PROC_FS)			+= proc.o
> diff --git a/arch/riscv/kernel/cpu/proc.c b/arch/riscv/kernel/cpu/proc.c
> new file mode 100644
> index 000000000000..4661190c43d1
> --- /dev/null
> +++ b/arch/riscv/kernel/cpu/proc.c
> @@ -0,0 +1,28 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/smp.h>
> +#include <linux/timex.h>
> +#include <linux/string.h>
> +#include <linux/seq_file.h>
> +#include <linux/cpufreq.h>
> +#include <linux/proc_fs.h>
> +#include <asm/usercfi.h>
> +
> +#ifdef CONFIG_RISCV_USER_CFI
> +
> +void arch_proc_pid_thread_features(struct seq_file *m, struct task_struct *task)
> +{
> +	seq_puts(m, "riscv_thread_features:\t");
> +	if (is_shstk_enabled(task))
> +		seq_puts(m, "shstk_enabled ");

According to Documentation/arch/x86/shstk.rst, x86 is avoiding the 
'_enabled' postfix here:

x86_Thread_features: shstk wrss

> +
> +	if (is_indir_lp_enabled(task))
> +		seq_puts(m, "lpad_enabled ");
> +
> +	seq_putc(m, '\n');
> +
> +	seq_puts(m, "riscv_thread_features_locked:\t");
> +	is_shstk_locked(task) ? seq_puts(m, "shstk_locked ") : seq_puts(m, "shstk_unlocked ");
> +	is_indir_lp_locked(task) ? seq_puts(m, "lpad_locked ") : seq_puts(m, "lpad_unlocked ");

Why do we need any entry for an unlocked feature in 
riscv_thread_features_locked?

Best regards

Heinrich

> +	seq_putc(m, '\n');
> +}
> +#endif /* CONFIG_RISCV_USER_CFI */
> 
> ---
> base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
> change-id: 20251017-proc_status-df1aedc85c7c
> --
> - debug
>