linux-kernel - Re: [PATCH 2/3] x86/asm/entry/32: Remove most of SYSCALL32 code, part 1

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Message-ID: <CALCETrXgEAPiAJ2LtGiWvrSNE9krcP3w--5UQRq5Cd-mtA9Tfw@mail.gmail.com>
Date:	Sat, 25 Jul 2015 12:33:08 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Krzysztof A. Sobiecki" <sobkas@...il.com>,
	Steven Rostedt <rostedt@...dmis.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 2/3] x86/asm/entry/32: Remove most of SYSCALL32 code, part 1

On Sat, Jul 25, 2015 at 11:36 AM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
> On 07/24/2015 07:50 PM, Andy Lutomirski wrote:
>> On Fri, Jul 24, 2015 at 6:47 AM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
>>> SYSCALL32 code is nearly identical to SYSCALL32, except for initial
>>> section. Merge them.
>>>
>>> The removal is split into two parts, to make review eaiser. This is part 1.
>>>
>>> auditsys_entry_common and auditsys_exit macros are indented one more tab without
>>> any changes. This prevents diff from becoming unreadable.
>>> They will be removed in part 2.
>>
>> I need to read these more closely, which is, at present, exceeding my
>> ability to look at asm.  (See the big NMI thread.)  I'll look soon.
>
> The "sysenter_fix_flags" thingy prevented the diff from being
> a pure delete, so it is not as clear as I hoped.
>
> What patch is doing is actually very simple. It "amputates"
> entire SYSENTER code path after it finished creating partially
> filled pt_regs, loaded arg6 and dealt with EFLAGS sanitization -
> after this is done, the state is identical to the similar
> state in SYSCALL code, so we can just use SYSCALL code from that moment
> onward! :)
>

I certainly agree that your patches are a nice cleanup.  I just want
to make sure there isn't something subtle and undocumented going on
there.

>
>> Meanwhile, this code is incredibly fragile wrt syscall restart.
>> (Syscall restart on compat is really weird.)
>
> Weird in what way?

See:

https://lkml.kernel.org/g/20110821084230.GI2203@ZenIV.linux.org.uk

--Andy
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