linux-kernel - Re: [PATCH v2 2/2] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

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Message-ID: <alpine.DEB.2.20.1707041744510.9000@nanos>
Date:   Tue, 4 Jul 2017 17:46:35 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Matt Fleming <matt@...eblueprint.co.uk>
cc:     Baoquan He <bhe@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>, thgarnie@...gle.com,
        caoj.fnst@...fujitsu.com, izumi.taku@...fujitsu.com
Subject: Re: [PATCH v2 2/2] x86/boot/KASLR: Restrict kernel to be randomized
 in mirror regions

On Tue, 4 Jul 2017, Matt Fleming wrote:
> On Tue, 04 Jul, at 04:46:58PM, Thomas Gleixner wrote:
> > On Tue, 4 Jul 2017, Baoquan He wrote:
> >  
> > > In fact I just referred to code in setup_arch(). Now I have a question,
> > > though CONFIG_EFI=y but efi firmware is not enabled,
> > > boot_params.efi_info.efi_loader_signature should be initilized to 0.
> > > Then below code is also problematic.
> > >
> > > #ifdef CONFIG_EFI
> > >         if (!strncmp((char *)&boot_params.efi_info.efi_loader_signature,                                                                         
> > >                      EFI32_LOADER_SIGNATURE, 4)) {
> > >                 set_bit(EFI_BOOT, &efi.flags);
> > >         } else if (!strncmp((char *)&boot_params.efi_info.efi_loader_signature,
> > >                      EFI64_LOADER_SIGNATURE, 4)) {
> > >                 set_bit(EFI_BOOT, &efi.flags);
> > >                 set_bit(EFI_64BIT, &efi.flags);
> > >         }
> > > 
> > >         if (efi_enabled(EFI_BOOT))
> > >                 efi_memblock_x86_reserve_range();
> > > #endif
> > 
> > Indeed. Matt?
> 
> It's possibly that I'm missing some context, but boot_params should be
> zero'd -- the x86 boot protocol requires that the entire data
> structure be zero'd on allocation.
> 
> Have I missed something?

No. I misread the code. The strncmp() operates on
boot_params.efi_info.efi_loader_signature itself, so yes, all is fine.

It's just Baoquans copy and paste wreckage which is busted.

Thanks,

	tglx