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

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Date:   Wed, 19 May 2021 20:10:11 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Yu-cheng Yu <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 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?

> +int arch_setup_elf_property(struct arch_elf_state *state)
> +{
> +	int r = 0;
> +
> +	if (!IS_ENABLED(CONFIG_X86_SHADOW_STACK))
> +		return r;
> +
> +	memset(&current->thread.cet, 0, sizeof(struct cet_status));
> +
> +	if (static_cpu_has(X86_FEATURE_SHSTK)) {

	cpu_feature_enabled

> +		if (state->gnu_property & GNU_PROPERTY_X86_FEATURE_1_SHSTK)
> +			r = shstk_setup();
> +	}
> +
> +	return r;
> +}
> +#endif

...

> 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...

-- 
Regards/Gruss,
    Boris.

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