linux-kernel - Re: [PATCH 7/7] x86/entry/64: extend register clearing on syscall entry to lower registers

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Date:   Fri, 30 Mar 2018 12:10:20 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Dominik Brodowski <linux@...inikbrodowski.net>
Cc:     linux-kernel@...r.kernel.org, viro@...IV.linux.org.uk,
        torvalds@...ux-foundation.org, arnd@...db.de,
        linux-arch@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <ak@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Brian Gerst <brgerst@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH 7/7] x86/entry/64: extend register clearing on syscall
 entry to lower registers


* Dominik Brodowski <linux@...inikbrodowski.net> wrote:

>  	.endif
>  	pushq	\rdx		/* pt_regs->dx */
> +	xorl	%edx, %edx	/* nosepc   dx */
>  	pushq   %rcx		/* pt_regs->cx */
> +	xorl	%ecx, %ecx	/* nosepc   cx */
>  	pushq   \rax		/* pt_regs->ax */
>  	pushq   %r8		/* pt_regs->r8 */
>  	xorl	%r8d, %r8d	/* nospec   r8 */
> diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
> index 08425c42f8b7..23e0945959e5 100644
> --- a/arch/x86/entry/entry_64_compat.S
> +++ b/arch/x86/entry/entry_64_compat.S
> @@ -220,8 +220,11 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe)
>  	pushq	%rax			/* pt_regs->orig_ax */
>  	pushq	%rdi			/* pt_regs->di */
>  	pushq	%rsi			/* pt_regs->si */
> +	xorl	%esi, %esi		/* nosepc   si */
>  	pushq	%rdx			/* pt_regs->dx */
> +	xorl	%edx, %edx		/* nosepc   dx */
>  	pushq	%rbp			/* pt_regs->cx (stashed in bp) */
> +	xorl	%ecx, %ecx		/* nosepc   cx */
>  	pushq	$-ENOSYS		/* pt_regs->ax */
>  	pushq   $0			/* pt_regs->r8  = 0 */
>  	xorl	%r8d, %r8d		/* nospec   r8 */
> @@ -365,8 +368,11 @@ ENTRY(entry_INT80_compat)
>  
>  	pushq	(%rdi)			/* pt_regs->di */
>  	pushq	%rsi			/* pt_regs->si */
> +	xorl	%esi, %esi		/* nosepc   si */
>  	pushq	%rdx			/* pt_regs->dx */
> +	xorl	%edx, %edx		/* nosepc   dx */
>  	pushq	%rcx			/* pt_regs->cx */
> +	xorl	%ecx, %ecx		/* nosepc   cx */
>  	pushq	$-ENOSYS		/* pt_regs->ax */
>  	pushq   $0			/* pt_regs->r8  = 0 */
>  	xorl	%r8d, %r8d		/* nospec   r8 */

s/nosepc
 /nospec

Thanks,

	Ingo