linux-kernel - Re: [PATCH v26 26/30] ELF: Introduce arch_setup_elf

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Date:   Wed, 19 May 2021 15:14:58 -0700
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        Haitao Huang <haitao.huang@...el.com>,
        Mark Brown <broonie@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH v26 26/30] ELF: Introduce arch_setup_elf_property()

On 5/19/2021 11:10 AM, Borislav Petkov wrote:
> On Tue, Apr 27, 2021 at 01:43:11PM -0700, Yu-cheng Yu wrote:
>> @@ -1951,6 +1951,8 @@ config X86_SHADOW_STACK
>>   	depends on AS_WRUSS
>>   	depends on ARCH_HAS_SHADOW_STACK
>>   	select ARCH_USES_HIGH_VMA_FLAGS
>> +	select ARCH_USE_GNU_PROPERTY
>> +	select ARCH_BINFMT_ELF_STATE
> 		^^^^^^^^
> 
> What's that for? Isn't ARCH_USE_GNU_PROPERTY enough?
> 

ARCH_USE_GNU_PROPERTY is for defining parsing functions, e.g.
	arch_parse_elf_property(),
	arch_setup_property().

ARCH_BINFMT_ELF_STATE is for defining "struct arch_elf_state".

However, those parsing functions take (struct arch_elf_state *) as an 
input.  It probably makes sense to have ARCH_USE_GNU_PROPERTY dependent 
on ARCH_BINFMT_ELF_STATE.  It would be ok as-is too.  ARM people might 
have other plans in mind.

[...]

> 
>> diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
>> index 30f68b42eeb5..24ba55ba8278 100644
>> --- a/include/uapi/linux/elf.h
>> +++ b/include/uapi/linux/elf.h
>> @@ -455,4 +455,13 @@ typedef struct elf64_note {
>>   /* Bits for GNU_PROPERTY_AARCH64_FEATURE_1_BTI */
>>   #define GNU_PROPERTY_AARCH64_FEATURE_1_BTI	(1U << 0)
>>   
>> +/* .note.gnu.property types for x86: */
>> +#define GNU_PROPERTY_X86_FEATURE_1_AND		0xc0000002
> 
> Why not 0xc0000001? ARM64 is 0xc0000000...
> 

I just looked at the ABI document.

ARM has GNU_PROPERTY_AARCH64_FEATURE_1_AND 0xc0000000

X86 has:
	GNU_PROPERTY_X86_ISA_1_USED	0xc0000000
	GNU_PROPERTY_X86_ISA_1_NEEDED	0xc0000001
	GNU_PROPERTY_X86_FEATURE_1_AND	0xc0000002

Yu-cheng