linux-kernel - Re: [PATCH] x86/mpx: Correctly report do_mpx_bt

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Date:   Fri, 21 Apr 2017 07:30:09 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Joerg Roedel <jroedel@...e.de>
Cc:     Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/mpx: Correctly report do_mpx_bt_fault() failures to
 user-space

On 04/21/2017 05:19 AM, Joerg Roedel wrote:
> On Thu, Apr 20, 2017 at 08:45:28AM -0700, Dave Hansen wrote:
>> How about doing X86_TRAP_PF?  That would at least be consistent with
>> SIGBUS, which is probably the closest thing to a generic error code that
>> we have.
> Correct me if I am wrong, but for SIGBUS this only happens in the
> page-fault path, right? And this path is indeed entered on a #PF
> exception.

It can happen to programs for tons of reasons.  It definitely happens
outside page faults.

> I see no reason to lie to user-space about the trap_nr that caused the
> SIGSEGV, especially since user-space software needs to be modified to
> make use of MPX, including the signal handler. So there is no risk of
> introducing any incompatibility or regression, no?

I think it's pretty safe to change.