linux-kernel - Re: [PATCH V3 3/5] x86/efi: Permanently save the EFI_MEMORY

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Message-ID: <alpine.DEB.2.21.1809051505030.1416@nanos.tec.linutronix.de>
Date:   Wed, 5 Sep 2018 15:06:06 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
cc:     Peter Zijlstra <peterz@...radead.org>,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        "Neri, Ricardo" <ricardo.neri@...el.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Al Stone <astone@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Bhupesh Sharma <bhsharma@...hat.com>
Subject: Re: [PATCH V3 3/5] x86/efi: Permanently save the EFI_MEMORY_MAP
 passed by the firmware

On Wed, 5 Sep 2018, Ard Biesheuvel wrote:
> On 5 September 2018 at 14:56, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Wed, Sep 05, 2018 at 02:27:49PM +0200, Ard Biesheuvel wrote:
> >> Would we still need to preserve the old memory map in that case?
> >
> > I thought the reason for having this was being able to know the fault is
> > in an EFI area. But of course, I'm not wel versed in this whole EFI
> > crapola.
> 
> I'm not entirely sure whether that really matters. The EFI services
> access the stack and can access byref/pointer arguments which are not
> covered by the EFI memory map as runtime services code/data, and so
> they can trigger page faults by running off the vmapped stack or
> writing to const byref arguments.
> 
> EFI runtime services using boot services regions after they are no
> longer available are a known source of headaches, but I don't see why
> we should restrict ourselves to such cases if we bother to wire up
> fault handling specifically for EFI services calls.
> 
> So any page or permission fault occurring in the context of a EFI
> runtime services invocation should be treated the same, I think.

I agree. Keep it simple. If the EFI crap fails, then assist with the reboot
and otherwise just kill it.

Thanks,

	tglx