linux-kernel - Re: [PATCH 01/16] x86/asm/64: Allocate and enable the SYSENTER stack

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Message-ID: <20171121104709.kjt4mzjgkm4rdwo6@pd.tnic>
Date:   Tue, 21 Nov 2017 11:47:09 +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 01/16] x86/asm/64: Allocate and enable the SYSENTER stack

On Mon, Nov 20, 2017 at 09:07:32AM -0800, Andy Lutomirski wrote:
> This will simplify future changes that want scratch variables early in
> the SYSENTER handler -- they'll be able to spill registers to the
> stack.  It also lets us get rid of a SWAPGS_UNSAFE_STACK user.
> 
> This does not depend on CONFIG_IA32_EMULATION because we'll want the
> stack space even without IA32 emulation.
> 
> As far as I can tell, the reason that this wasn't done from day 1 is
> that we use IST for #DB and #BP, which is IMO rather nasty and causes
> a lot more problems than it solves.  But, since #DB uses IST, we don't
> actually need a real stack for SYSENTER (because SYSENTER with TF set
> will invoke #DB on the IST stack rather than the SYSENTER stack).
> I want to remove IST usage from these vectors some day, and this patch
> is a prerequisite for that as well.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/entry/entry_64_compat.S | 2 +-
>  arch/x86/include/asm/processor.h | 3 ---
>  arch/x86/kernel/asm-offsets.c    | 5 +++++
>  arch/x86/kernel/asm-offsets_32.c | 5 -----
>  arch/x86/kernel/cpu/common.c     | 4 +++-
>  arch/x86/kernel/process.c        | 2 --
>  arch/x86/kernel/traps.c          | 3 +--
>  7 files changed, 10 insertions(+), 14 deletions(-)

Reviewed-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

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