linux-kernel - Re: Avoid speculative indirect calls in kernel

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Date:   Mon, 8 Jan 2018 21:53:02 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andrea Arcangeli <aarcange@...hat.com>
cc:     Jon Masters <jcm@...hat.com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andi Kleen <andi@...stfloor.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...el.com>, Jeff Law <law@...hat.com>,
        Nick Clifton <nickc@...hat.com>
Subject: Re: Avoid speculative indirect calls in kernel

On Mon, 8 Jan 2018, Andrea Arcangeli wrote:
> On Fri, Jan 05, 2018 at 10:59:28AM +0100, Thomas Gleixner wrote:
> I sent you a better version of the efi_64.c fix from Jiri privately
> and you still miss the tboot fix in linux-tip so you still got a boot
> failure to fix there.

Missed that in the pile ...

> This is incremental with
> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/log/?h=WIP.x86/pti
> where the "Unbreak EFI old_memmap" fix is applied.
> 
> I respinned it after doing the more correct fix in this case too (same
> as the efi_64.c improvement) while leaving the attribution to the fix
> to Dave as he did the hard part.

Thanks for resending it.

> >From 0c480d1eeabd56379144a4ed6b6fb24f3b84e40e Mon Sep 17 00:00:00 2001
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> Date: Sat, 6 Jan 2018 18:41:14 +0100
> Subject: [PATCH 1/1] x86/kaiser/efi: unbreak tboot
> 
> This is another case similar to what EFI does: create a new set of
> page tables, map some code at a low address, and jump to it.  PTI
> mistakes this low address for userspace and mistakenly marks it
> non-executable in an effort to make it unusable for userspace.  Undo
> the poison to allow execution.
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Ning Sun <ning.sun@...el.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: x86@...nel.org
> Cc: tboot-devel@...ts.sourceforge.net
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
> ---
>  arch/x86/kernel/tboot.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/kernel/tboot.c b/arch/x86/kernel/tboot.c
> index a4eb27918ceb..75869a4b6c41 100644
> --- a/arch/x86/kernel/tboot.c
> +++ b/arch/x86/kernel/tboot.c
> @@ -127,6 +127,7 @@ static int map_tboot_page(unsigned long vaddr, unsigned long pfn,
>  	p4d = p4d_alloc(&tboot_mm, pgd, vaddr);
>  	if (!p4d)
>  		return -1;
> +	pgd->pgd &= ~_PAGE_NX;
>  	pud = pud_alloc(&tboot_mm, p4d, vaddr);
>  	if (!pud)
>  		return -1;
> 
> If I can help and assist in any other way let me know.
> 
> Thanks,
> Andrea
>