From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933532AbcAKQve (ORCPT ); Mon, 11 Jan 2016 11:51:34 -0500 Received: from foss.arm.com ([217.140.101.70]:56853 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932510AbcAKQvb (ORCPT ); Mon, 11 Jan 2016 11:51:31 -0500 Date: Mon, 11 Jan 2016 16:51:04 +0000 From: Mark Rutland To: Ard Biesheuvel Cc: Kees Cook , Arnd Bergmann , kernel-hardening@lists.openwall.com, Sharma Bhupesh , Catalin Marinas , Will Deacon , "linux-kernel@vger.kernel.org" , Leif Lindholm , Stuart Yoder , Marc Zyngier , Christoffer Dall , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v3 04/21] arm64: decouple early fixmap init from linear mapping Message-ID: <20160111165103.GA29503@leverpostej> References: <1452518355-4606-1-git-send-email-ard.biesheuvel@linaro.org> <1452518355-4606-5-git-send-email-ard.biesheuvel@linaro.org> <20160111160906.GO6499@leverpostej> <20160111162737.GQ6499@leverpostej> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160111162737.GQ6499@leverpostej> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 11, 2016 at 04:27:38PM +0000, Mark Rutland wrote: > On Mon, Jan 11, 2016 at 05:15:13PM +0100, Ard Biesheuvel wrote: > > On 11 January 2016 at 17:09, Mark Rutland wrote: > > > On Mon, Jan 11, 2016 at 02:18:57PM +0100, Ard Biesheuvel wrote: > > >> Since the early fixmap page tables are populated using pages that are > > >> part of the static footprint of the kernel, they are covered by the > > >> initial kernel mapping, and we can refer to them without using __va/__pa > > >> translations, which are tied to the linear mapping. > > >> > > >> Since the fixmap page tables are disjoint from the kernel mapping up > > >> to the top level pgd entry, we can refer to bm_pte[] directly, and there > > >> is no need to walk the page tables and perform __pa()/__va() translations > > >> at each step. > > >> > > >> Signed-off-by: Ard Biesheuvel > > >> --- > > >> arch/arm64/mm/mmu.c | 32 ++++++-------------- > > >> 1 file changed, 9 insertions(+), 23 deletions(-) > > >> > > >> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > > >> index 7711554a94f4..75b5f0dc3bdc 100644 > > >> --- a/arch/arm64/mm/mmu.c > > >> +++ b/arch/arm64/mm/mmu.c > > >> @@ -570,38 +570,24 @@ void vmemmap_free(unsigned long start, unsigned long end) > > >> #endif /* CONFIG_SPARSEMEM_VMEMMAP */ > > >> > > >> static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss; > > >> -#if CONFIG_PGTABLE_LEVELS > 2 > > >> static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss; > > >> -#endif > > >> -#if CONFIG_PGTABLE_LEVELS > 3 > > >> static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss; > > >> -#endif > > >> > > >> static inline pud_t * fixmap_pud(unsigned long addr) > > >> { > > >> - pgd_t *pgd = pgd_offset_k(addr); > > >> - > > >> - BUG_ON(pgd_none(*pgd) || pgd_bad(*pgd)); > > >> - > > >> - return pud_offset(pgd, addr); > > >> + return (CONFIG_PGTABLE_LEVELS > 3) ? &bm_pud[pud_index(addr)] > > >> + : (pud_t *)pgd_offset_k(addr); > > > > > > If we move patch 6 earlier, we could use pud_offset_kimg here, and avoid > > > the cast, at the cost of passing the pgd into fixmap_pud. > > > > > > Similarly for fixmap_pmd. > > > > > > > Is that necessarily an improvement? I know it hides the cast, but I > > think having an explicit pgd_t* to pud_t* cast that so obviously > > applies to CONFIG_PGTABLE_LEVELS < 4 only is fine as well. > > True; it's not a big thing either way. Sorry, I'm gonig to change my mind on that again. I think using p?d_offset_kimg is preferable. e.g. static inline pud_t * fixmap_pud(unsigned long addr) { pgd_t *pgd = pgd_offset_k(addr); BUG_ON(pgd_none(*pgd) || pgd_bad(*pgd)); return pud_offset_kimg(pgd, addr); } static inline pmd_t * fixmap_pmd(unsigned long addr) { pud_t *pud = fixmap_pud(addr); BUG_ON(pud_none(*pud) || pud_bad(*pud)); return pmd_offset_kimg(pud, addr); } That avoids having to check CONFIG_PGTABLE_LEVELS check and perform a cast, avoids duplicating details about bm_{pud,pmd}, and keeps the existing structure so it's easier to reason about the change. I was wrong about having to pass the pgd or pud in, so callers don't need upating. >>From my PoV that is preferable. Thanks, Mark. From mboxrd@z Thu Jan 1 00:00:00 1970 From: mark.rutland@arm.com (Mark Rutland) Date: Mon, 11 Jan 2016 16:51:04 +0000 Subject: [PATCH v3 04/21] arm64: decouple early fixmap init from linear mapping In-Reply-To: <20160111162737.GQ6499@leverpostej> References: <1452518355-4606-1-git-send-email-ard.biesheuvel@linaro.org> <1452518355-4606-5-git-send-email-ard.biesheuvel@linaro.org> <20160111160906.GO6499@leverpostej> <20160111162737.GQ6499@leverpostej> Message-ID: <20160111165103.GA29503@leverpostej> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Jan 11, 2016 at 04:27:38PM +0000, Mark Rutland wrote: > On Mon, Jan 11, 2016 at 05:15:13PM +0100, Ard Biesheuvel wrote: > > On 11 January 2016 at 17:09, Mark Rutland wrote: > > > On Mon, Jan 11, 2016 at 02:18:57PM +0100, Ard Biesheuvel wrote: > > >> Since the early fixmap page tables are populated using pages that are > > >> part of the static footprint of the kernel, they are covered by the > > >> initial kernel mapping, and we can refer to them without using __va/__pa > > >> translations, which are tied to the linear mapping. > > >> > > >> Since the fixmap page tables are disjoint from the kernel mapping up > > >> to the top level pgd entry, we can refer to bm_pte[] directly, and there > > >> is no need to walk the page tables and perform __pa()/__va() translations > > >> at each step. > > >> > > >> Signed-off-by: Ard Biesheuvel > > >> --- > > >> arch/arm64/mm/mmu.c | 32 ++++++-------------- > > >> 1 file changed, 9 insertions(+), 23 deletions(-) > > >> > > >> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > > >> index 7711554a94f4..75b5f0dc3bdc 100644 > > >> --- a/arch/arm64/mm/mmu.c > > >> +++ b/arch/arm64/mm/mmu.c > > >> @@ -570,38 +570,24 @@ void vmemmap_free(unsigned long start, unsigned long end) > > >> #endif /* CONFIG_SPARSEMEM_VMEMMAP */ > > >> > > >> static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss; > > >> -#if CONFIG_PGTABLE_LEVELS > 2 > > >> static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss; > > >> -#endif > > >> -#if CONFIG_PGTABLE_LEVELS > 3 > > >> static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss; > > >> -#endif > > >> > > >> static inline pud_t * fixmap_pud(unsigned long addr) > > >> { > > >> - pgd_t *pgd = pgd_offset_k(addr); > > >> - > > >> - BUG_ON(pgd_none(*pgd) || pgd_bad(*pgd)); > > >> - > > >> - return pud_offset(pgd, addr); > > >> + return (CONFIG_PGTABLE_LEVELS > 3) ? &bm_pud[pud_index(addr)] > > >> + : (pud_t *)pgd_offset_k(addr); > > > > > > If we move patch 6 earlier, we could use pud_offset_kimg here, and avoid > > > the cast, at the cost of passing the pgd into fixmap_pud. > > > > > > Similarly for fixmap_pmd. > > > > > > > Is that necessarily an improvement? I know it hides the cast, but I > > think having an explicit pgd_t* to pud_t* cast that so obviously > > applies to CONFIG_PGTABLE_LEVELS < 4 only is fine as well. > > True; it's not a big thing either way. Sorry, I'm gonig to change my mind on that again. I think using p?d_offset_kimg is preferable. e.g. static inline pud_t * fixmap_pud(unsigned long addr) { pgd_t *pgd = pgd_offset_k(addr); BUG_ON(pgd_none(*pgd) || pgd_bad(*pgd)); return pud_offset_kimg(pgd, addr); } static inline pmd_t * fixmap_pmd(unsigned long addr) { pud_t *pud = fixmap_pud(addr); BUG_ON(pud_none(*pud) || pud_bad(*pud)); return pmd_offset_kimg(pud, addr); } That avoids having to check CONFIG_PGTABLE_LEVELS check and perform a cast, avoids duplicating details about bm_{pud,pmd}, and keeps the existing structure so it's easier to reason about the change. I was wrong about having to pass the pgd or pud in, so callers don't need upating. >>From my PoV that is preferable. Thanks, Mark. From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com Date: Mon, 11 Jan 2016 16:51:04 +0000 From: Mark Rutland Message-ID: <20160111165103.GA29503@leverpostej> References: <1452518355-4606-1-git-send-email-ard.biesheuvel@linaro.org> <1452518355-4606-5-git-send-email-ard.biesheuvel@linaro.org> <20160111160906.GO6499@leverpostej> <20160111162737.GQ6499@leverpostej> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160111162737.GQ6499@leverpostej> Subject: [kernel-hardening] Re: [PATCH v3 04/21] arm64: decouple early fixmap init from linear mapping To: Ard Biesheuvel Cc: Kees Cook , Arnd Bergmann , kernel-hardening@lists.openwall.com, Sharma Bhupesh , Catalin Marinas , Will Deacon , "linux-kernel@vger.kernel.org" , Leif Lindholm , Stuart Yoder , Marc Zyngier , Christoffer Dall , "linux-arm-kernel@lists.infradead.org" List-ID: On Mon, Jan 11, 2016 at 04:27:38PM +0000, Mark Rutland wrote: > On Mon, Jan 11, 2016 at 05:15:13PM +0100, Ard Biesheuvel wrote: > > On 11 January 2016 at 17:09, Mark Rutland wrote: > > > On Mon, Jan 11, 2016 at 02:18:57PM +0100, Ard Biesheuvel wrote: > > >> Since the early fixmap page tables are populated using pages that are > > >> part of the static footprint of the kernel, they are covered by the > > >> initial kernel mapping, and we can refer to them without using __va/__pa > > >> translations, which are tied to the linear mapping. > > >> > > >> Since the fixmap page tables are disjoint from the kernel mapping up > > >> to the top level pgd entry, we can refer to bm_pte[] directly, and there > > >> is no need to walk the page tables and perform __pa()/__va() translations > > >> at each step. > > >> > > >> Signed-off-by: Ard Biesheuvel > > >> --- > > >> arch/arm64/mm/mmu.c | 32 ++++++-------------- > > >> 1 file changed, 9 insertions(+), 23 deletions(-) > > >> > > >> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > > >> index 7711554a94f4..75b5f0dc3bdc 100644 > > >> --- a/arch/arm64/mm/mmu.c > > >> +++ b/arch/arm64/mm/mmu.c > > >> @@ -570,38 +570,24 @@ void vmemmap_free(unsigned long start, unsigned long end) > > >> #endif /* CONFIG_SPARSEMEM_VMEMMAP */ > > >> > > >> static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss; > > >> -#if CONFIG_PGTABLE_LEVELS > 2 > > >> static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss; > > >> -#endif > > >> -#if CONFIG_PGTABLE_LEVELS > 3 > > >> static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss; > > >> -#endif > > >> > > >> static inline pud_t * fixmap_pud(unsigned long addr) > > >> { > > >> - pgd_t *pgd = pgd_offset_k(addr); > > >> - > > >> - BUG_ON(pgd_none(*pgd) || pgd_bad(*pgd)); > > >> - > > >> - return pud_offset(pgd, addr); > > >> + return (CONFIG_PGTABLE_LEVELS > 3) ? &bm_pud[pud_index(addr)] > > >> + : (pud_t *)pgd_offset_k(addr); > > > > > > If we move patch 6 earlier, we could use pud_offset_kimg here, and avoid > > > the cast, at the cost of passing the pgd into fixmap_pud. > > > > > > Similarly for fixmap_pmd. > > > > > > > Is that necessarily an improvement? I know it hides the cast, but I > > think having an explicit pgd_t* to pud_t* cast that so obviously > > applies to CONFIG_PGTABLE_LEVELS < 4 only is fine as well. > > True; it's not a big thing either way. Sorry, I'm gonig to change my mind on that again. I think using p?d_offset_kimg is preferable. e.g. static inline pud_t * fixmap_pud(unsigned long addr) { pgd_t *pgd = pgd_offset_k(addr); BUG_ON(pgd_none(*pgd) || pgd_bad(*pgd)); return pud_offset_kimg(pgd, addr); } static inline pmd_t * fixmap_pmd(unsigned long addr) { pud_t *pud = fixmap_pud(addr); BUG_ON(pud_none(*pud) || pud_bad(*pud)); return pmd_offset_kimg(pud, addr); } That avoids having to check CONFIG_PGTABLE_LEVELS check and perform a cast, avoids duplicating details about bm_{pud,pmd}, and keeps the existing structure so it's easier to reason about the change. I was wrong about having to pass the pgd or pud in, so callers don't need upating. >>From my PoV that is preferable. Thanks, Mark.