Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753080AbbKQIv3 (ORCPT ); Tue, 17 Nov 2015 03:51:29 -0500 Received: from www.linutronix.de ([62.245.132.108]:45331 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752315AbbKQIv2 (ORCPT ); Tue, 17 Nov 2015 03:51:28 -0500 Date: Tue, 17 Nov 2015 09:50:36 +0100 (CET) From: Thomas Gleixner To: Borislav Petkov cc: Matt Fleming , Ingo Molnar , "H . Peter Anvin" , Toshi Kani , linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org, Sai Praneeth Prakhya , Dave Hansen Subject: Re: [PATCH v2 1/5] x86/mm/pageattr: Ensure cpa->pfn only contains page frame numbers In-Reply-To: Message-ID: References: <1447538451-5793-1-git-send-email-matt@codeblueprint.co.uk> <1447538451-5793-2-git-send-email-matt@codeblueprint.co.uk> <20151116212042.GE20435@pd.tnic> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2299 Lines: 57 On Mon, 16 Nov 2015, Thomas Gleixner wrote: > On Mon, 16 Nov 2015, Borislav Petkov wrote: > > On Mon, Nov 16, 2015 at 09:19:01PM +0100, Thomas Gleixner wrote: > > > On Sat, 14 Nov 2015, Matt Fleming wrote: > > > > The x86 pageattr code is confused about the data that is stored > > > > cpa->pfn, sometimes it's treated as a page frame number, sometimes > > > > it's treated as an unshifted physical address, and in one place it's > > > > treated as a pte. > > > > > > Yuck. > > > > This paragraph should read like this instead: > > > > "Boris used cpa->pfn as a scratch variable to contain the physical > > address. He realizes now that he should've added a separate > > cpa_data.phys_addr then, instead of confusing everybody." > > > > > > The result of this is that the mapping functions do not map the > > > > intended physical address. > > > > > > > > This isn't a problem in practice because most of the addresses we're > > > > mapping in the EFI code paths are already mapped in 'trampoline_pgd' > > > > and so the pageattr mappings functions don't actually do anything in > > > > this case. But when we move to using a separate page table for the EFI > > > > runtime this will be an issue. > > > > > > Are you sure that this does not affect existing kernel versions? > > > > Shouldn't because with this new patchset we're copying all the PGDs from > > the kernel page table before doing an EFI call, see > > efi_sync_low_kernel_mappings() in patch 5. > > > > > > while (num_pages-- && start < end) { > > > > - > > > > - /* deal with the NX bit */ > > > > - if (!(pgprot_val(pgprot) & _PAGE_NX)) > > > > - cpa->pfn &= ~_PAGE_NX; > > > > > > That should be a seperate patch because this is just bogus code and > > > has nothing to do with the pfn confusion. > > > > Why bogus? > > Even with cpa->pfn used as an address it cannot ever be set as the > address is page aligned .... Gah. Misread it. _PAGE_NX is bit 63 and it can be set when cpa->pfn is abused as an address. So yes, it should go away with that patch. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/