Date: Thu, 11 Jan 2018 22:44:39 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Steven Sistare <steven.sistare@oracle.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Pavel Tatashin <pasha.tatashin@oracle.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Hugh Dickins <hughd@google.com>, Thomas Voegtle <tv@lio96.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Shuah Khan <shuahkh@osg.samsung.com>, patches@kernelci.org,
        Ben Hutchings <ben.hutchings@codethink.co.uk>,
        lkft-triage@lists.linaro.org, stable <stable@vger.kernel.org>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH 4.4 00/37] 4.4.110-stable review
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On Thu, 11 Jan 2018, Steven Sistare wrote:
> On 1/11/2018 3:46 PM, Linus Torvalds wrote:
> > On Thu, Jan 11, 2018 at 12:37 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> >>
> >> 67a9108ed431 ("x86/efi: Build our own page table structures")
> >>
> >> got rid of EFI depending on real_mode_header->trampoline_pgd
> > 
> > So I think it only got rid of by default - the codepath is still
> > there, the allocation is still there, it's just that it's not actually
> > used unless somebody does that "efi=old_mmap" thing.
> > 
> > Looking around, there's at least one quirk for the SGI UV1 system that
> > enables EFI_OLD_MMAP automatically. There might be others that I
> > missed, but I think that's it.
> > 
> > So it *can* trigger without "efi=old_mmap", but not on any normal machines.
> > 
> > And as Pavel points out, even when the bug is active, it's pretty hard
> > to actually trigger.
> > 
> > But yeah, there may be other EFI patches that I didn't notice that
> > changed things in other ways too.
> > 
> >                Linus
> 
> The bug is not present in the latest upstream kernel because the efi_pgd is
> correctly aligned:
> 
>   arch/x86/platform/efi/efi_64.c
>     int __init efi_alloc_page_tables(void)
>       efi_pgd = (pgd_t *)__get_free_pages(gfp_mask, PGD_ALLOCATION_ORDER);

Yes, I came exactly to the same conclusion, but I didn't want to call Linus
a moron before I triple checked that trampoline_pgd is still there, but
only every used to get out of the realmode swamp at bpot.

Thanks,

	tglx