linux-kernel - Re: [PATCHv2] x86/mm: set x32 syscall bit in SET

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Message-ID: <20170321171723.GB21564@uranus.lan>
Date:   Tue, 21 Mar 2017 20:17:23 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Dmitry Safonov <dsafonov@...tuozzo.com>
Cc:     linux-kernel@...r.kernel.org, 0x7f454c46@...il.com,
        Adam Borowski <kilobyte@...band.pl>, linux-mm@...ck.org,
        Andrei Vagin <avagin@...il.com>, Borislav Petkov <bp@...e.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCHv2] x86/mm: set x32 syscall bit in SET_PERSONALITY()

On Tue, Mar 21, 2017 at 07:37:12PM +0300, Dmitry Safonov wrote:
...
> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> index d6b784a5520d..d3d4d9abcaf8 100644
> --- a/arch/x86/kernel/process_64.c
> +++ b/arch/x86/kernel/process_64.c
> @@ -519,8 +519,14 @@ void set_personality_ia32(bool x32)
>  		if (current->mm)
>  			current->mm->context.ia32_compat = TIF_X32;
>  		current->personality &= ~READ_IMPLIES_EXEC;
> -		/* in_compat_syscall() uses the presence of the x32
> -		   syscall bit flag to determine compat status */
> +		/*
> +		 * in_compat_syscall() uses the presence of the x32
> +		 * syscall bit flag to determine compat status.
> +		 * On the bitness of syscall relies x86 mmap() code,
> +		 * so set x32 syscall bit right here to make
> +		 * in_compat_syscall() work during exec().
> +		 */
> +		task_pt_regs(current)->orig_ax |= __X32_SYSCALL_BIT;
>  		current->thread.status &= ~TS_COMPAT;

Hi! I must admit I didn't follow close the overall series (so can't
comment much here :) but I have a slightly unrelated question -- is
there a way to figure out if task is running in x32 mode say with
some ptrace or procfs sign?