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

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Date:   Thu, 20 May 2021 11:26:25 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
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 Wed, May 19, 2021 at 03:14:58PM -0700, Yu, Yu-cheng wrote:
> However, those parsing functions take (struct arch_elf_state *) as an input.

Exactly.

> 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.

Well, let's look at ARM, ARM64 in particular. They have defined struct
arch_elf_state without the ifdeffery in

arch/arm64/include/asm/elf.h

and are using that struct in arch_parse_elf_property().

And they have selected ARCH_BINFMT_ELF_STATE just so that they disable
those dummy accessors in fs/binfmt_elf.c

And you're practically glueing together ARCH_BINFMT_ELF_STATE and
ARCH_USE_GNU_PROPERTY. However, all the functionality is for adding
the gnu property note so I think you should select both but only use
ARCH_USE_GNU_PROPERTY in all the ifdeffery in your patch to at least
have this as simple as possible.

> I just looked at the ABI document.

Which document is that? Link?

> 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

Our defines should at least have a comment pointing to that document.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette