Re: [PATCH v15 04/13] arch/x86: add syscall_get_arch to syscall.h

From: Will Drewry <wad@chromium.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-doc@vger.kernel.org, kernel-hardening@lists.openwall.com,
	netdev@vger.kernel.org, x86@kernel.org, arnd@arndb.de,
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	mcgrathr@chromium.org, tglx@linutronix.de, luto@mit.edu,
	eparis@redhat.com, serge.hallyn@canonical.com, djm@mindrot.org,
	scarybeasts@gmail.com, indan@nul.nu, pmoore@redhat.com,
	akpm@linux-foundation.org, corbet@lwn.net,
	eric.dumazet@gmail.com, markus@chromium.org,
	coreyb@linux.vnet.ibm.com, keescook@chromium.org
Subject: Re: [PATCH v15 04/13] arch/x86: add syscall_get_arch to syscall.h
Date: Wed, 11 Apr 2012 10:41:24 -0500	[thread overview]
Message-ID: <CABqD9haw2YutkSQHO0Qq19eveqwKCEi=L3fpCYupqvakW3jDMw@mail.gmail.com> (raw)
In-Reply-To: <4F84F895.4080101@zytor.com>

On Tue, Apr 10, 2012 at 10:20 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 04/10/2012 08:13 PM, Will Drewry wrote:
>> On Sun, Mar 25, 2012 at 2:34 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>>> On 03/14/2012 08:11 PM, Will Drewry wrote:
>>>>
>>>> +static inline int syscall_get_arch(struct task_struct *task,
>>>> +                                struct pt_regs *regs)
>>>> +{
>>>> +#ifdef CONFIG_IA32_EMULATION
>>>> +     /*
>>>> +      * TS_COMPAT is set for 32-bit syscall entries and then
>>>> +      * remains set until we return to user mode.
>>>> +      *
>>>> +      * TIF_IA32 tasks should always have TS_COMPAT set at
>>>> +      * system call time.
>>>> +      */
>>>> +     if (task_thread_info(task)->status & TS_COMPAT)
>>>> +             return AUDIT_ARCH_I386;
>>>> +#endif
>>>> +     return AUDIT_ARCH_X86_64;
>>>> +}
>>>>  #endif       /* CONFIG_X86_32 */
>>>>
>>>>  #endif       /* _ASM_X86_SYSCALL_H */
>>>
>>> Just one FYI on this: after the x32 changes are upstream this can be
>>> implemented in terms of is_ia32_task().
>>
>> Now that I've seen is_ia32_task(), it appears to be exactly the same as above:
>> (1)  If we're x86_32, it's ia32
>> (2)  If we're x86_64, ia32 == !!(status & TS_COMPAT)
>> (3)  Otherwise, it's x86_64, including x32
>>
>> Am I missing something? Should is_ia32_task(void) take a task_struct?
>> Right now, I don't see any reason to change the code, as posted, but
>> maybe I am mis-reading?
>>
>
> Sorry, answered the wrong question.  Yes, it is the same as above...
> just wandered if we could centralize this test.  It might indeed make
> sense to provide general predicates which take a task pointer.

Makes sense to me. I'm leaving this specific patch alone at present.

That said, a quick grep shows only  a handful of ia32 references:
./arch/x86/include/asm/compat.h:        return is_ia32_task() || is_x32_task();
./arch/x86/ia32/ia32_signal.c:  bool ia32 = is_ia32_task();
./arch/x86/kernel/ptrace.c:     if (!is_ia32_task())

Would it make sense to make a new predicate or just expand the one
added in 3.4 to take a task_struct parameter? I'm not sure if there'd
be much fallout in converting these from directly checking
current_thread_info to task_thread_info.

It's a small patch either way.

cheers!
will