From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751989AbdLFPjb (ORCPT ); Wed, 6 Dec 2017 10:39:31 -0500 Received: from mx2.suse.de ([195.135.220.15]:57481 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751444AbdLFPj0 (ORCPT ); Wed, 6 Dec 2017 10:39:26 -0500 Date: Wed, 6 Dec 2017 16:39:12 +0100 From: Borislav Petkov To: Thomas Gleixner Cc: LKML , x86@kernel.org, Linus Torvalds , Andy Lutomirsky , Peter Zijlstra , Dave Hansen , Greg KH , keescook@google.com, hughd@google.com, Brian Gerst , Josh Poimboeuf , Denys Vlasenko , Rik van Riel , Boris Ostrovsky , Juergen Gross , David Laight , Eduardo Valentin , aliguori@amazon.com, Will Deacon , daniel.gruss@iaik.tugraz.at Subject: Re: [patch 36/60] x86/mm/kpti: Add functions to clone kernel PMDs Message-ID: <20171206153911.en56fuvm72rfrpi4@pd.tnic> References: <20171204140706.296109558@linutronix.de> <20171204150607.803765853@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20171204150607.803765853@linutronix.de> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 04, 2017 at 03:07:42PM +0100, Thomas Gleixner wrote: > From: Andy Lutomirski > > Provide infrastructure to: > > - find a kernel PMD for a mapping which must be visible to user space for > the entry/exit code to work. > > - walk an address range and share the kernel PMD with it. > > This reuses a small part of the original KAISER patches to populate the > user space page table. > > [ tglx: Made it universally usable so it can be used for any kind of shared > mapping. Add a mechanism to clear specific bits in the user space > visible PMD entry. ] > > Originally-by: Dave Hansen > Signed-off-by: Andy Lutomirski > Signed-off-by: Thomas Gleixner > > --- > arch/x86/mm/kpti.c | 102 +++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 102 insertions(+) > > --- a/arch/x86/mm/kpti.c > +++ b/arch/x86/mm/kpti.c > @@ -65,6 +65,108 @@ void __init kpti_check_boottime_disable( > } > > /* > + * Walk the user copy of the page tables (optionally) trying to allocate > + * page table pages on the way down. > + * > + * Returns a pointer to a PMD on success, or NULL on failure. > + */ > +static pmd_t *kpti_user_pagetable_walk_pmd(unsigned long address) > +{ > + pgd_t *pgd = kernel_to_user_pgdp(pgd_offset_k(address)); > + gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO); > + pud_t *pud; > + p4d_t *p4d; > + > + if (address < PAGE_OFFSET) { > + WARN_ONCE(1, "attempt to walk user address\n"); > + return NULL; > + } > + > + if (pgd_none(*pgd)) { > + WARN_ONCE(1, "All user pgds should have been populated\n"); > + return NULL; > + } > + BUILD_BUG_ON(pgd_large(*pgd) != 0); Must be some 5LEVEL thing? Because it currently does: static inline int pgd_large(pgd_t pgd) { return 0; } > + > + p4d = p4d_offset(pgd, address); > + BUILD_BUG_ON(p4d_large(*p4d) != 0); That too. > + if (p4d_none(*p4d)) { > + unsigned long new_pud_page = __get_free_page(gfp); > + if (!new_pud_page) > + return NULL; > + > + if (p4d_none(*p4d)) { We already tested that above or does __get_free_page() have side-effects? > + set_p4d(p4d, __p4d(_KERNPG_TABLE | __pa(new_pud_page))); > + new_pud_page = 0; > + } > + if (new_pud_page) > + free_page(new_pud_page); > + } > + > + pud = pud_offset(p4d, address); > + /* The user page tables do not use large mappings: */ > + if (pud_large(*pud)) { > + WARN_ON(1); > + return NULL; > + } > + if (pud_none(*pud)) { > + unsigned long new_pmd_page = __get_free_page(gfp); > + if (!new_pmd_page) > + return NULL; > + > + if (pud_none(*pud)) { Ditto. -- Regards/Gruss, Boris. SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --