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Date:   Mon, 3 Oct 2022 15:37:57 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc:     x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
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        "Ravi V . Shankar" <ravi.v.shankar@intel.com>,
        Weijiang Yang <weijiang.yang@intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        joao.moreira@intel.com, John Allen <john.allen@amd.com>,
        kcc@google.com, eranian@google.com, rppt@kernel.org,
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Subject: Re: [PATCH v2 30/39] x86: Expose thread features status in
 /proc/$PID/arch_status
Message-ID: <202210031530.9CFB62B39F@keescook>
References: <20220929222936.14584-1-rick.p.edgecombe@intel.com>
 <20220929222936.14584-31-rick.p.edgecombe@intel.com>
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On Thu, Sep 29, 2022 at 03:29:27PM -0700, Rick Edgecombe wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> 
> Applications and loaders can have logic to decide whether to enable CET.
> They usually don't report whether CET has been enabled or not, so there
> is no way to verify whether an application actually is protected by CET
> features.
> 
> Add two lines in /proc/$PID/arch_status to report enabled and locked
> features.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> [Switched to CET, added to commit log]
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.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