linux-kernel - Re: [PATCH v3 7/7] x86/ldt,ptrace: provide regset access to the LDT

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Date:   Fri, 22 Jun 2018 08:05:52 -0700
From:   hpa@...or.com
To:     Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <h.peter.anvin@...el.com>
CC:     LKML <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Lutomirski <luto@...nel.org>,
        "Bae, Chang Seok" <chang.seok.bae@...el.com>,
        "Metzger, Markus T" <markus.t.metzger@...el.com>
Subject: Re: [PATCH v3 7/7] x86/ldt,ptrace: provide regset access to the LDT

On June 22, 2018 7:49:13 AM PDT, Andy Lutomirski <luto@...nel.org> wrote:
>On Thu, Jun 21, 2018 at 2:18 PM H. Peter Anvin, Intel
><h.peter.anvin@...el.com> wrote:
>>
>> From: "H. Peter Anvin" <hpa@...ux.intel.com>
>>
>> Provide ptrace/regset access to the LDT, if one exists.  This
>> interface provides both read and write access. The write code is
>> unified with modify_ldt(); the read code doesn't have enough
>> similarity so it has been kept made separate.
>
>For this and for the GDT, you've chosen to use struct user_desc as
>your format instead of using a native hardware descriptor format.  Any
>particular reason why?  If nothing else, it will bloat core files a
>bit more than needed.

I did because REGSET_TLS was implemented that way, and that is simply a subset of the GDT (which made the same code trivially applicable to both.) modify_ldt() does it *both* ways for extra fun (one for reading, and one for writing.)

->active is defined as "beyond this point the regset contains only the default value", which seemed appropriate in this case.
-- 
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