linux-kernel - Re: [PATCH RESEND 2/2] x86/mm: Randomize va with generic arch_pick_mmap

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Date:   Tue, 21 Sep 2021 16:41:45 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     sxwjean@...com
Cc:     x86@...nel.org, linux-mm@...ck.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, luto@...nel.org,
        krisman@...labora.com, chang.seok.bae@...el.com,
        viro@...iv.linux.org.uk, nivedita@...m.mit.edu,
        adobriyan@...il.com, oleg@...hat.com, sblbir@...zon.com,
        axboe@...nel.dk, laijs@...ux.alibaba.com,
        dave.hansen@...ux.intel.com, akpm@...ux-foundation.org,
        arnd@...db.de, davem@...emloft.net, keescook@...omium.org,
        kim.phillips@....com, yazen.ghannam@....com, dave@...olabs.net,
        metze@...ba.org, elver@...gle.com, ebiederm@...ssion.com,
        christophe.leroy@...roup.eu, linux-kernel@...r.kernel.org,
        Xiongwei Song <sxwjean@...il.com>
Subject: Re: [PATCH RESEND 2/2] x86/mm: Randomize va with generic
 arch_pick_mmap_layout()

On Tue, Sep 21, 2021 at 10:34:14PM +0800, sxwjean@...com wrote:
> diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h
> index 7516e4199b3c..c697e377644d 100644
> --- a/arch/x86/include/asm/compat.h
> +++ b/arch/x86/include/asm/compat.h
> @@ -151,6 +151,11 @@ struct compat_shmid64_ds {
>  	compat_ulong_t __unused5;
>  };
>  
> +static inline int is_compat_task(void)
> +{
> +	return IS_ENABLED(CONFIG_COMPAT) && test_thread_flag(TIF_32BIT);
> +}
> +

This is still fundamentally broken for x86. x86 doesn't have compat
tasks, the granularity is at syscall at best.