linux-kernel - Re: [PATCH 02/24] x86/mm/kaiser: Prepare the x86/entry assembly code for entry/exit CR3 switching

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20171127173146.plbdbiuzkv5ctgw6@hirez.programming.kicks-ass.net>
Date:   Mon, 27 Nov 2017 18:31:46 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...capital.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 02/24] x86/mm/kaiser: Prepare the x86/entry assembly code
 for entry/exit CR3 switching

On Mon, Nov 27, 2017 at 11:49:01AM +0100, Ingo Molnar wrote:
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index caf74a1bb3de..df0152bee8a8 100644

> @@ -198,6 +201,14 @@ ENTRY(entry_SYSCALL_64)
>  
>  	swapgs
>  	movq	%rsp, PER_CPU_VAR(rsp_scratch)
> +
> +	/*
> +	 * The kernel CR3 is needed to map the process stack, but we
> +	 * need a scratch register to be able to load CR3.  %rsp is
> +	 * clobberable right now, so use it as a scratch register.
> +	 * %rsp will look crazy here for a couple instructions.
> +	 */
> +	SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
>  	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
>  
>  	/* Construct struct pt_regs on stack */

I think we can do away with this one, on account of never getting here
because of entry_SYSCALL_64_trampoline.