From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752520AbcHLSXH (ORCPT ); Fri, 12 Aug 2016 14:23:07 -0400 Received: from mail-wm0-f48.google.com ([74.125.82.48]:38677 "EHLO mail-wm0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751652AbcHLSXG (ORCPT ); Fri, 12 Aug 2016 14:23:06 -0400 MIME-Version: 1.0 In-Reply-To: <1470937490-7375-1-git-send-email-catalin.marinas@arm.com> References: <1470937490-7375-1-git-send-email-catalin.marinas@arm.com> From: Kees Cook Date: Fri, 12 Aug 2016 11:23:03 -0700 X-Google-Sender-Auth: mCLpihj7DthharQnCMTxcYX4keg Message-ID: Subject: Re: [PATCH] arm64: Introduce execute-only page access permissions To: Catalin Marinas Cc: "linux-arm-kernel@lists.infradead.org" , Linux-MM , LKML , Will Deacon Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 11, 2016 at 10:44 AM, Catalin Marinas wrote: > The ARMv8 architecture allows execute-only user permissions by clearing > the PTE_UXN and PTE_USER bits. However, the kernel running on a CPU > implementation without User Access Override (ARMv8.2 onwards) can still > access such page, so execute-only page permission does not protect > against read(2)/write(2) etc. accesses. Systems requiring such > protection must enable features like SECCOMP. So, UAO CPUs will bypass this protection in userspace if using read/write on a memory-mapped file? I'm just trying to make sure I understand the bypass scenario. And is this something that can be fixed? If we add exec-only, I feel like it shouldn't have corner case surprises. :) -Kees > > This patch changes the arm64 __P100 and __S100 protection_map[] macros > to the new __PAGE_EXECONLY attributes. A side effect is that > pte_user() no longer triggers for __PAGE_EXECONLY since PTE_USER isn't > set. To work around this, the check is done on the PTE_NG bit via the > pte_ng() macro. VM_READ is also checked now for page faults. > > Cc: Will Deacon > Signed-off-by: Catalin Marinas > --- > arch/arm64/include/asm/pgtable-prot.h | 5 +++-- > arch/arm64/include/asm/pgtable.h | 10 +++++----- > arch/arm64/mm/fault.c | 5 ++--- > mm/mmap.c | 5 +++++ > 4 files changed, 15 insertions(+), 10 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h > index 39f5252673f7..2142c7726e76 100644 > --- a/arch/arm64/include/asm/pgtable-prot.h > +++ b/arch/arm64/include/asm/pgtable-prot.h > @@ -70,12 +70,13 @@ > #define PAGE_COPY_EXEC __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN) > #define PAGE_READONLY __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN) > #define PAGE_READONLY_EXEC __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN) > +#define PAGE_EXECONLY __pgprot(_PAGE_DEFAULT | PTE_NG | PTE_PXN) > > #define __P000 PAGE_NONE > #define __P001 PAGE_READONLY > #define __P010 PAGE_COPY > #define __P011 PAGE_COPY > -#define __P100 PAGE_READONLY_EXEC > +#define __P100 PAGE_EXECONLY > #define __P101 PAGE_READONLY_EXEC > #define __P110 PAGE_COPY_EXEC > #define __P111 PAGE_COPY_EXEC > @@ -84,7 +85,7 @@ > #define __S001 PAGE_READONLY > #define __S010 PAGE_SHARED > #define __S011 PAGE_SHARED > -#define __S100 PAGE_READONLY_EXEC > +#define __S100 PAGE_EXECONLY > #define __S101 PAGE_READONLY_EXEC > #define __S110 PAGE_SHARED_EXEC > #define __S111 PAGE_SHARED_EXEC > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index dbb1b7bf1b07..403a61cf4967 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -74,7 +74,7 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]; > #define pte_write(pte) (!!(pte_val(pte) & PTE_WRITE)) > #define pte_exec(pte) (!(pte_val(pte) & PTE_UXN)) > #define pte_cont(pte) (!!(pte_val(pte) & PTE_CONT)) > -#define pte_user(pte) (!!(pte_val(pte) & PTE_USER)) > +#define pte_ng(pte) (!!(pte_val(pte) & PTE_NG)) > > #ifdef CONFIG_ARM64_HW_AFDBM > #define pte_hw_dirty(pte) (pte_write(pte) && !(pte_val(pte) & PTE_RDONLY)) > @@ -85,8 +85,8 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]; > #define pte_dirty(pte) (pte_sw_dirty(pte) || pte_hw_dirty(pte)) > > #define pte_valid(pte) (!!(pte_val(pte) & PTE_VALID)) > -#define pte_valid_not_user(pte) \ > - ((pte_val(pte) & (PTE_VALID | PTE_USER)) == PTE_VALID) > +#define pte_valid_global(pte) \ > + ((pte_val(pte) & (PTE_VALID | PTE_NG)) == PTE_VALID) > #define pte_valid_young(pte) \ > ((pte_val(pte) & (PTE_VALID | PTE_AF)) == (PTE_VALID | PTE_AF)) > > @@ -179,7 +179,7 @@ static inline void set_pte(pte_t *ptep, pte_t pte) > * Only if the new pte is valid and kernel, otherwise TLB maintenance > * or update_mmu_cache() have the necessary barriers. > */ > - if (pte_valid_not_user(pte)) { > + if (pte_valid_global(pte)) { > dsb(ishst); > isb(); > } > @@ -213,7 +213,7 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr, > pte_val(pte) &= ~PTE_RDONLY; > else > pte_val(pte) |= PTE_RDONLY; > - if (pte_user(pte) && pte_exec(pte) && !pte_special(pte)) > + if (pte_ng(pte) && pte_exec(pte) && !pte_special(pte)) > __sync_icache_dcache(pte, addr); > } > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > index c8beaa0da7df..58f697fe18b6 100644 > --- a/arch/arm64/mm/fault.c > +++ b/arch/arm64/mm/fault.c > @@ -245,8 +245,7 @@ static int __do_page_fault(struct mm_struct *mm, unsigned long addr, > good_area: > /* > * Check that the permissions on the VMA allow for the fault which > - * occurred. If we encountered a write or exec fault, we must have > - * appropriate permissions, otherwise we allow any permission. > + * occurred. > */ > if (!(vma->vm_flags & vm_flags)) { > fault = VM_FAULT_BADACCESS; > @@ -281,7 +280,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, > struct task_struct *tsk; > struct mm_struct *mm; > int fault, sig, code; > - unsigned long vm_flags = VM_READ | VM_WRITE | VM_EXEC; > + unsigned long vm_flags = VM_READ | VM_WRITE; > unsigned int mm_flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE; > > if (notify_page_fault(regs, esr)) > diff --git a/mm/mmap.c b/mm/mmap.c > index ca9d91bca0d6..69cad562cd00 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -88,6 +88,11 @@ static void unmap_region(struct mm_struct *mm, > * w: (no) no w: (no) no w: (copy) copy w: (no) no > * x: (no) no x: (no) yes x: (no) yes x: (yes) yes > * > + * On arm64, PROT_EXEC has the following behaviour for both MAP_SHARED and > + * MAP_PRIVATE: > + * r: (no) no > + * w: (no) no > + * x: (yes) yes > */ > pgprot_t protection_map[16] = { > __P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111, -- Kees Cook Nexus Security