linux-kernel - Re: [PATCH?] uprobes: change uprobe_write

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: <529F7527.5040201@zytor.com>
Date:	Wed, 04 Dec 2013 10:32:07 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Oleg Nesterov <oleg@...hat.com>, Hugh Dickins <hughd@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH?] uprobes: change uprobe_write_opcode() to modify the
 page directly

On 12/04/2013 09:15 AM, Linus Torvalds wrote:
> On Wed, Dec 4, 2013 at 8:54 AM, H. Peter Anvin <hpa@...or.com> wrote:
>>
>> That is why I talk about the atomic instruction word... most (but not
>> *all*) architectures have a fundamental minimum unit of instructions
>> which is aligned and can be atomically written.  Typically this is 1, 2,
>> or 4 bytes.
> 
> Note that it's not just about the "atomically written", it's also
> about the guarantee that it's atomically *read*.
> 
> x86 can certainly atomically write a 4-byte instruction too, it's just
> that there's no guarantee - even if the instruction is aligned etc -
> that the actual instruction decoding always ends up reading it that
> way. It might re-read an instruction after encountering a prefix byte
> etc etc. So even if it's all properly aligned, the reading side might
> do something odd.
> 

True, at least in theory, but the atomic instruction quantum on x86 is a
byte.

	-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/