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Subject: Re: [PATCH v26 26/30] ELF: Introduce arch_setup_elf_property()
To:     Borislav Petkov <bp@alien8.de>
Cc:     x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
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        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Balbir Singh <bsingharora@gmail.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
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        Jonathan Corbet <corbet@lwn.net>,
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        Mike Kravetz <mike.kravetz@oracle.com>,
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        Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
        Dave Martin <Dave.Martin@arm.com>,
        Weijiang Yang <weijiang.yang@intel.com>,
        Pengfei Xu <pengfei.xu@intel.com>,
        Haitao Huang <haitao.huang@intel.com>,
        Mark Brown <broonie@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>
References: <20210427204315.24153-1-yu-cheng.yu@intel.com>
 <20210427204315.24153-27-yu-cheng.yu@intel.com> <YKVUgzJ0MVNBgjDd@zn.tnic>
From:   "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
Message-ID: <c29348d8-caae-5226-d095-ae3992d88338@intel.com>
Date:   Wed, 19 May 2021 15:14:58 -0700
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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