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

From: "Andy Lutomirski" <luto@kernel.org>
To: "Kees Cook" <keescook@chromium.org>,
	"Rick P Edgecombe" <rick.p.edgecombe@intel.com>
Cc: "the arch/x86 maintainers" <x86@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	linux-doc@vger.kernel.org, linux-mm@kvack.org,
	linux-arch@vger.kernel.org,
	"Linux API" <linux-api@vger.kernel.org>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"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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	"Randy Dunlap" <rdunlap@infradead.org>,
	"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
	"Weijiang Yang" <weijiang.yang@intel.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	"Moreira, Joao" <joao.moreira@intel.com>,
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	"kcc@google.com" <kcc@google.com>,
	"Eranian, Stephane" <eranian@google.com>,
	"Mike Rapoport" <rppt@kernel.org>,
	jamorris@linux.microsoft.com, dethoma@microsoft.com
Subject: Re: [PATCH v2 30/39] x86: Expose thread features status in /proc/$PID/arch_status
Date: Mon, 03 Oct 2022 15:45:50 -0700	[thread overview]
Message-ID: <b8b3caab-9f0c-4230-8d7b-debd7f79cdb9@app.fastmail.com> (raw)
In-Reply-To: <202210031530.9CFB62B39F@keescook>

On Mon, Oct 3, 2022, at 3:37 PM, Kees Cook wrote:
> 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.

I think I meant that, since it's "arch_status" not "x86_status", the fields should have names like "x86.Thread_features".  Otherwise if another architecture adds a Thread_features field, then anything running under something like qemu userspace emulation could be confused.

Assuming that's what I meant, I think my comment still stands :)