linux-kernel - Re: [RFC] gcc feature request: Moving blocks into sections

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:	Mon, 05 Aug 2013 21:28:32 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>, gcc <gcc@....gnu.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Daney <ddaney.cavm@...il.com>,
	Behan Webster <behanw@...verseincode.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [RFC] gcc feature request: Moving blocks into sections

On 08/05/2013 09:14 PM, Mathieu Desnoyers wrote:
>>
>> For unconditional jmp that should be pretty safe barring any fundamental
>> changes to the instruction set, in which case we can enable it as
>> needed, but for extra robustness it probably should skip prefix bytes.
> 
> On x86-32, some prefixes are actually meaningful. AFAIK, the 0x66 prefix
> is used for:
> 
> E9 cw   jmp rel16   relative jump, only in 32-bit
> 
> Other prefixes can probably be safely skipped.
> 

Yes.  Some of them are used as hints or for MPX.

> Another question is whether anything prevents the assembler from
> generating a jump near (absolute indirect), or far jump. The code above
> seems to assume that we have either a short or near relative jump.

Absolutely something prevents!  It would be a very serious error for the
assembler to generate such instructions.

	-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/