Re: [PATCH v2 30/39] x86: Expose thread features status in /proc/$PID/arch_status

[Kees Cook]

On Thu, Sep 29, 2022 at 03:29:27PM -0700, Rick Edgecombe wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> 
> Applications and loaders can have logic to decide whether to enable CET.
> They usually don't report whether CET has been enabled or not, so there
> is no way to verify whether an application actually is protected by CET
> features.
> 
> Add two lines in /proc/$PID/arch_status to report enabled and locked
> features.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> [Switched to CET, added to commit log]
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> 
> ---
> 
> v2:
>  - New patch
> 
>  arch/x86/kernel/Makefile     |  2 ++
>  arch/x86/kernel/fpu/xstate.c | 47 ---------------------------
>  arch/x86/kernel/proc.c       | 63 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 65 insertions(+), 47 deletions(-)
>  create mode 100644 arch/x86/kernel/proc.c

This is two patches: one to create proc.c, the other to add CET support.

I found where the "arch_status" conversation was:
https://lore.kernel.org/all/CALCETrUjF9PBmkzH1J86vw4ZW785DP7FtcT+gcSrx29=BUnjoQ@xxxxxxxxxxxxxx/

Andy, what did you mean "make sure that everything in it is namespaced"?
Everything already has a field name. And arch_status doesn't exactly
solve having compat fields -- it still needs to be handled manually?
Anyway... we have arch_status, so I guess it's fine.

> [...]
> +int proc_pid_arch_status(struct seq_file *m, struct pid_namespace *ns,
> +			struct pid *pid, struct task_struct *task)
> +{
> +	/*
> +	 * Report AVX512 state if the processor and build option supported.
> +	 */
> +	if (cpu_feature_enabled(X86_FEATURE_AVX512F))
> +		avx512_status(m, task);
> +
> +	seq_puts(m, "Thread_features:\t");
> +	dump_features(m, task->thread.features);
> +	seq_putc(m, '\n');
> +
> +	seq_puts(m, "Thread_features_locked:\t");
> +	dump_features(m, task->thread.features_locked);
> +	seq_putc(m, '\n');

Why are these always present instead of ifdefed?

-Kees

-- 
Kees Cook