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

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

On 10/23/25 01:38, Deepak Gupta wrote:
> Hi Hienrich,
> 
> 
> On Tue, Oct 21, 2025 at 01:13:36PM +0200, Heinrich Schuchardt wrote:
>> 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?
> 
> Just following what x86 did. I believe shadow stack and landing pad are 
> there
> in arm64, x86 and riscv. So probably /proc/<pid>/status is best place.
>>
>> 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/.
> 
> Will do.
> 
>>
>>>
>>> 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
> 
> I can follow same and use `shstk`. We don't have `wrss` because
> shadow stack is writeable by right instruction (sspush and ssamoswap) in
> riscv.
> 
>>
>>> +
>>> +    if (is_indir_lp_enabled(task))
>>> +        seq_puts(m, "lpad_enabled ");
> 
> Would you prefer similar here. Just "lpad"?

That would be consistent with what is done for x86.

Best regards

Heinrich

> 
>>> +
>>> +    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?
> 
> absence of "feature_locked" is considered unlocked, then I can drop it.
> 
>>
>> Best regards
>>
>> Heinrich
>>
>>> +    seq_putc(m, '\n');
>>> +}
>>> +#endif /* CONFIG_RISCV_USER_CFI */
>>>
>>> ---
>>> base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
>>> change-id: 20251017-proc_status-df1aedc85c7c
>>> -- 
>>> - debug
>>>
>>