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Date: Wed, 22 Mar 2017 13:49:17 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Thomas Garnier <thgarnie@...gle.com>
Cc: Andy Lutomirski <luto@...capital.net>, Ingo Molnar <mingo@...nel.org>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
David Howells <dhowells@...hat.com>, Arnd Bergmann <arnd@...db.de>,
Al Viro <viro@...iv.linux.org.uk>, Dave Hansen <dave.hansen@...el.com>,
René Nyffenegger <mail@...enyffenegger.ch>,
Andrew Morton <akpm@...ux-foundation.org>,
Kees Cook
<keescook@...omium.org>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
Andy Lutomirski <luto@...nel.org>,
Ard Biesheuvel
<ard.biesheuvel@...aro.org>,
Nicolas Pitre <nicolas.pitre@...aro.org>,
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"David A . Long" <dave.long@...aro.org>,
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Andre Przywara <andre.przywara@....com>,
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linux-s390 <linux-s390@...r.kernel.org>,
LKML
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Linux API <linux-api@...r.kernel.org>,
the arch/x86 maintainers <x86@...nel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v3 2/4] x86/syscalls: Specific usage of
verify_pre_usermode_state
On 03/22/17 13:41, Thomas Garnier wrote:
>>> with the change below for additional feedback.
>>
>> Can you specify what that means?
>
> If I set inline by default, the compiler chose not to inline it on
> x86. If I force inline the size impact was actually bigger (without
> the architecture specific code).
>
That's utterly bizarre. Something strange is going on there. I suspect
the right thing to do is to out-of-line the error case only, but even
that seems strange. It should be something like four instructions inline.
>>
>> On x86, where there is only one caller of this, it really seems like it
>> ought to reduce the overhead to almost zero (since it most likely is
>> hidden in the pipeline.)
>>
>> I would like to suggest defining it inline if
>> CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE is set; I really don't
>> care about an architecture which doesn't have it.
>
> But if there is only one caller, does the compiler is not suppose to
> inline the function based on options?
If it is marked static in the same file, yes, but you have it in a
different file from what I can tell.
> The assembly will call it too, so I would need an inline and a
> non-inline based on the caller.
Where? I don't see that anywhere, at least for x86.
-hpa
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