linux-kernel - Re: [PATCH] x86: vdso32/syscall.S: do not load __USER32

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Message-ID: <CALCETrXq7uxDCu5GCzVoyijuYQ9yoWkRbyPY1=rBFptgtWjQng@mail.gmail.com>
Date:	Mon, 23 Mar 2015 13:38:37 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: vdso32/syscall.S: do not load __USER32_DS to %ss

On Mon, Mar 23, 2015 at 12:37 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Mon, Mar 23, 2015 at 9:47 AM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
>> This vDSO code only gets used by 64-bit kernel,
>> not 32-bit. In 64-bit kernels, data segment is the same
>> for 32-bit and 64-bit userspace, and SYSRET insn does load %ss
>> with its selector. No need to repeat it by hand. Segment loads
>> are somewhat expensive: tens of cycles.
>>
>> Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
>> CC: Linus Torvalds <torvalds@...ux-foundation.org>
>> CC: Steven Rostedt <rostedt@...dmis.org>
>> CC: Ingo Molnar <mingo@...nel.org>
>> CC: Borislav Petkov <bp@...en8.de>
>> CC: "H. Peter Anvin" <hpa@...or.com>
>> CC: Andy Lutomirski <luto@...capital.net>
>> CC: Oleg Nesterov <oleg@...hat.com>
>> CC: Frederic Weisbecker <fweisbec@...il.com>
>> CC: Alexei Starovoitov <ast@...mgrid.com>
>> CC: Will Drewry <wad@...omium.org>
>> CC: Kees Cook <keescook@...omium.org>
>> CC: x86@...nel.org
>> CC: linux-kernel@...r.kernel.org
>> ---
>>
>> Patch was run-tested.
>
> Applied, thanks.

Actually, I want to remove the added comment in the code.  I don't see
why we should have a specific comment about SS and not about, say, CS,
ESP, or anything else.  OK?

>
> --Andy



-- 
Andy Lutomirski
AMA Capital Management, LLC
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