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From:   Andy Lutomirski <luto@kernel.org>
Date:   Wed, 15 Apr 2020 18:07:01 -0700
Message-ID: <CALCETrWTDrcynTwpWZ6u6JXRL1rz6_vakLK7=BqMjCPCkQ+9dg@mail.gmail.com>
Subject: Re: [RFC PATCH v2] x86/arch_prctl: Add ARCH_SET_XCR0 to set XCR0 per-thread
To:     Keno Fischer <keno@juliacomputing.com>
Cc:     Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andi Kleen <andi@firstfloor.org>,
        Kyle Huey <khuey@kylehuey.com>,
        "Robert O'Callahan" <robert@ocallahan.org>
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On Tue, Apr 14, 2020 at 5:10 PM Keno Fischer <keno@juliacomputing.com> wrote:
>
> > (why would you want to record with an unusual XCR0?)
>

Hmm.  I don't personally have a strong objection to allowing XCR0 to
be overridden as long as it's done reasonably sanely.  And maybe
requires a sysctl to be enabled.

Would it make matters easier if tasks with nonstandard XCR0 were not
allowed to use ptrace() at all?  And if ARCH_SET_XCR0 were disallowed
if the caller is tracing anyone?