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

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Message-Id: <b8b3caab-9f0c-4230-8d7b-debd7f79cdb9@app.fastmail.com>
Date:   Mon, 03 Oct 2022 15:45:50 -0700
From:   "Andy Lutomirski" <luto@...nel.org>
To:     "Kees Cook" <keescook@...omium.org>,
        "Rick P Edgecombe" <rick.p.edgecombe@...el.com>
Cc:     "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org,
        "Linux API" <linux-api@...r.kernel.org>,
        "Arnd Bergmann" <arnd@...db.de>,
        "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 (Intel)" <peterz@...radead.org>,
        "Randy Dunlap" <rdunlap@...radead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "Weijiang Yang" <weijiang.yang@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Moreira, Joao" <joao.moreira@...el.com>,
        "john.allen@....com" <john.allen@....com>,
        "kcc@...gle.com" <kcc@...gle.com>,
        "Eranian, Stephane" <eranian@...gle.com>,
        "Mike Rapoport" <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 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@...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.

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 :)