linux-kernel - Re: [PATCH resend] MIPS: Allow FPU emulator to use non-stack area.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 7 Oct 2014 17:22:01 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	David Daney <ddaney.cavm@...il.com>
Cc:	David Daney <david.daney@...ium.com>,
	Rich Felker <dalias@...c.org>,
	David Daney <david.s.daney@...il.com>,
	Matthew Fortune <Matthew.Fortune@...tec.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"libc-alpha@...rceware.org" <libc-alpha@...rceware.org>,
	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>,
	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>
Subject: Re: [PATCH resend] MIPS: Allow FPU emulator to use non-stack area.

On Oct 7, 2014 1:03 PM, "David Daney" <ddaney.cavm@...il.com> wrote:
>
> On 10/07/2014 12:28 PM, Andy Lutomirski wrote:
>>
>> On Tue, Oct 7, 2014 at 12:21 PM, Rich Felker <dalias@...c.org> wrote:
>>>
>>> On Tue, Oct 07, 2014 at 12:16:59PM -0700, Leonid Yegoshin wrote:
>>>>
>>>> On 10/07/2014 12:09 PM, Rich Felker wrote:
>>>>>
>>>>> I agree completely here. We should not break things (or, as it
>>>>> seems, leave them broken) for common usage cases that affect
>>>>> everyone just to coddle proprietary vendor-specific instructions.
>>>>> The latter just should not be used in delay slots unless the chip
>>>>> vendor also promises to provide fpu branch in hardware. Rich
>>>>
>>>> And what do you propose - remove a current in-stack emulation and
>>>> you still think it doesn't break a status-quo?
>>>
>>>
>>> The in-stack trampoline support could be left but used only for
>>> emulating instructions the kernel doesn't know. This would make all
>>> normal binaries immediately usable with non-executable stack, and
>>> would avoid the only potential source of regressions. Ultimately I
>>> think the "xol" stuff should be removed, but that could be a long term
>>> goal.
>>
>>
>> Does anything break if the xol stuff is disabled for PT_GNU_STACK tasks?
>>
>
> The instructions must be executed, if you turn on a non-executable stack, you cannot execute them on the stack, so they must be handled in another way, which is the subject of this thread.
>
> Options:
>
> 1a) XOL kernel manages the memory
> 1b) XOL userspace manages the menory
> 2) Emulate the instructions.
> 3) I don't think there is a 3rd. option.

4) SIGILL

5) single-step or use an HW breakpoint if available


But, yes, 3 seems reasonable.

--Andy
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/