linux-kernel - Re: [PATCH v2 30/39] x86: Expose thread features status in /proc/$PID/arch

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Date:   Mon, 3 Oct 2022 15:37:57 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H . J . Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V . Shankar" <ravi.v.shankar@...el.com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        joao.moreira@...el.com, John Allen <john.allen@....com>,
        kcc@...gle.com, eranian@...gle.com, rppt@...nel.org,
        jamorris@...ux.microsoft.com, dethoma@...rosoft.com
Subject: Re: [PATCH v2 30/39] x86: Expose thread features status in
 /proc/$PID/arch_status

On Thu, Sep 29, 2022 at 03:29:27PM -0700, Rick Edgecombe wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> 
> 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@...ux.intel.com>
> [Switched to CET, added to commit log]
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> 
> ---
> 
> 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@mail.gmail.com/

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