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

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Message-ID: <CALCETrWAptYpJ3_8jky0R7KHjr2TBVCgjkBg-4z4X_b31M-LJg@mail.gmail.com>
Date:	Tue, 25 Aug 2015 00:19:08 -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 Mon, Jul 27, 2015 at 12:26 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Mon, Jul 27, 2015 at 12:19 PM, 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.
>>>
>>> Meanwhile, this code is incredibly fragile wrt syscall restart.
>>> (Syscall restart on compat is really weird.)  Do we have a decent test
>>> for it?
>>
>> How about this? (Feel free to expand, this is a first cut only).
>
> On a very brief glance, it looks reasonable, but I'd try it with
> recvfrom instead of recv because it's a six-argument syscall.
>

I was wondering how syscall restart works on compat syscalls on AMD
(i.e. SYSCALL32).  I think the answer is that it doesn't.  Sigh.
(Tested with ptrace instead of actual syscall restart.)

--Andy
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