linux-kernel - Re: [PATCH] Make math_state_restore() save and restore the interrupt flag

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]

Message-ID: <52ED4C96.6020703@zytor.com>
Date:	Sat, 01 Feb 2014 11:35:50 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Suresh Siddha <sbsiddha@...il.com>
CC:	Nate Eldredge <nate@...tsmathematics.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	stable <stable@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Maarten Baert <maarten-baert@...mail.com>,
	Jan Kara <jack@...e.cz>, George Spelvin <linux@...izon.com>,
	Pekka Riikonen <priikone@....fi>
Subject: Re: [PATCH] Make math_state_restore() save and restore the interrupt
 flag

On 02/01/2014 11:27 AM, Linus Torvalds wrote:
>
>   (a) "we don't want to restore at all, because once the kernel starts
> using math, it might do so a lot, and saving/restoring is a bad idea":
>
>    void __kernel_fpu_end(void)
>    {
>            stts();
>    }
>
> *or*
>
> Quite frankly, I'd almost lean towards (a). Comments? Does anybody
> have any loads where the kernel does a lot of fpu stuff (ie network
> encryption using the hw engines or something)? I'd really like to hear
> if it makes a difference..
>

This will obviously not protect eageronly features (MPX, LWP, ...) so 
this means those features are permanently unavailable to the kernel, 
even inside kernel_fpu_begin/end.  Now, currently I don't think we have 
any plans to use those in the kernel (at least not in a way where 
kernel_fpu_begin/end makes sense as bracketing), but it is something 
worth keeping in mind.

	-hpa

--
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/