linux-kernel - Re: [PATCH v10 37/38] compiler-gcc.h: Introduce _

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Message-ID: <20170718093631.pnamvdrkmzcjz64j@gmail.com>
Date:   Tue, 18 Jul 2017 11:36:31 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-efi@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org, kvm@...r.kernel.org,
        kasan-dev@...glegroups.com,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Dave Young <dyoung@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v10 37/38] compiler-gcc.h: Introduce __nostackp function
 attribute


* Tom Lendacky <thomas.lendacky@....com> wrote:

> Create a new function attribute, __nostackp, that can used to turn off
> stack protection on a per function basis.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  include/linux/compiler-gcc.h | 2 ++
>  include/linux/compiler.h     | 4 ++++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> index cd4bbe8..682063b 100644
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -166,6 +166,8 @@
>  
>  #if GCC_VERSION >= 40100
>  # define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
> +
> +#define __nostackp	__attribute__((__optimize__("no-stack-protector")))
>  #endif
>  
>  #if GCC_VERSION >= 40300
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 219f82f..63cbca1 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -470,6 +470,10 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
>  #define __visible
>  #endif
>  
> +#ifndef __nostackp
> +#define __nostackp
> +#endif

So I changed this from the hard to read and ambiguous "__nostackp" abbreviation 
(does it mean 'no stack pointer?') to "__nostackprotector", plus added this detail 
to the changelog:

| ( This is needed by the SME in-place kernel memory encryption feature,
|   which activates encryption in its sme_enable() function and thus changes the 
|   visible value of the stack protection cookie on function return. )

Agreed?

Thanks,

	Ingo