linux-kernel - Re: [PATCH v7 12/26] x86/fpu/xstate: Use feature disable (XFD) to protect dynamic user state

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Message-ID: <919EAEBF-61EF-4DC4-839C-08055C1A1F29@intel.com>
Date:   Sat, 17 Jul 2021 15:47:50 +0000
From:   "Bae, Chang Seok" <chang.seok.bae@...el.com>
To:     "Macieira, Thiago" <thiago.macieira@...el.com>
CC:     Borislav Petkov <bp@...e.de>, "Lutomirski, Andy" <luto@...nel.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "Brown, Len" <len.brown@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Liu, Jing2" <jing2.liu@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 12/26] x86/fpu/xstate: Use feature disable (XFD) to
 protect dynamic user state

On Jul 13, 2021, at 12:13, Macieira, Thiago <thiago.macieira@...el.com> wrote:
> On Saturday, 10 July 2021 06:02:59 PDT Chang S. Bae wrote:
>> 
>> +                               /* Raise a signal when it failed to handle.
>> */ +                               if (err)
>> +                                       force_sig(SIGSEGV);
>> +                       }
>> +                       return;
> 
> Can I make a suggestion that you send a different signal than SIGSEGV for the 
> failure of unauthorised instructions? I would recommend SIGILL. Additionally, 
> please consider a new ILL_* constant for the si_code field.

Applied on v8 [1].

> On the same topic, is there a way to save this state in a core dump? The FS 
> and GS bases would also be very handy.

According to [2],
    “Exporting the extended register state through ptrace and core-dump
     (NT_X86_XSTATE note) interfaces will be same"

Also, AMX state was found as I retrieved from my core-dump image.

Thanks,
Chang

[1] https://lore.kernel.org/lkml/20210717152903.7651-13-chang.seok.bae@intel.com/
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/include/asm/user.h#n26