linux-kernel - Re: [PATCH v2 09/18] x86/asm: Move SYSENTER_stack to the beginning of struct tss

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Date:   Thu, 23 Nov 2017 13:00:31 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v2 09/18] x86/asm: Move SYSENTER_stack to the beginning
 of struct tss_struct

On Tue, Nov 21, 2017 at 08:44:04PM -0800, Andy Lutomirski wrote:
> I want SYSENTER_stack to have reliable overflow detection, which
> means that it needs to be at the bottom of a page, not the top.

Passive-impersonal tone pls.

> Move it to the beginning of struct tss_struct and page-align it.
> 
> Also add an assertion to make sure that the fixed hardware TSS
> doesn't cross a page boundary.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/include/asm/processor.h | 21 ++++++++++++---------
>  arch/x86/kernel/cpu/common.c     | 22 ++++++++++++++++++++++
>  2 files changed, 34 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index d32a3c88a968..8f5dac9dfbdc 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -327,7 +327,16 @@ struct x86_hw_tss {
>  
>  struct tss_struct {
>  	/*
> -	 * The hardware state:
> +	 * Space for the temporary SYSENTER stack, used for SYSENTER
> +	 * and the entry trampoline as well.
> +	 */
> +	unsigned long		SYSENTER_stack_canary;
> +	unsigned long		SYSENTER_stack[64];
> +
> +	/*
> +	 * The fixed hardware portion.  This must not cross a page boundary
> +	 * at risk of violating the SDM's advice and potentially triggering
> +	 * errata.
>  	 */
>  	struct x86_hw_tss	x86_tss;
>  
> @@ -338,15 +347,9 @@ struct tss_struct {
>  	 * be within the limit.
>  	 */
>  	unsigned long		io_bitmap[IO_BITMAP_LONGS + 1];
> +} __attribute__((__aligned__(PAGE_SIZE)));

WARNING: __aligned(size) is preferred over __attribute__((aligned(size)))
#58: FILE: arch/x86/include/asm/processor.h:350:
+} __attribute__((__aligned__(PAGE_SIZE)));

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--