Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932252AbdDDQFZ (ORCPT ); Tue, 4 Apr 2017 12:05:25 -0400 Received: from mail-qk0-f179.google.com ([209.85.220.179]:34331 "EHLO mail-qk0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754975AbdDDQFW (ORCPT ); Tue, 4 Apr 2017 12:05:22 -0400 Subject: Re: [PATCH v3] arm64: print a fault message when attempting to write RO memory To: Stephen Boyd , Catalin Marinas , Will Deacon References: <20170404065803.4848-1-stephen.boyd@linaro.org> Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, James Morse , Mark Rutland From: Laura Abbott Message-ID: <3d7bc424-38b4-f71d-4308-1f6360499bea@redhat.com> Date: Tue, 4 Apr 2017 09:05:17 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <20170404065803.4848-1-stephen.boyd@linaro.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4739 Lines: 136 On 04/03/2017 11:58 PM, Stephen Boyd wrote: > If a page is marked read only we should print out that fact, > instead of printing out that there was a page fault. Right now we > get a cryptic error message that something went wrong with an > unhandled fault, but we don't evaluate the esr to figure out that > it was a read/write permission fault. > > Instead of seeing: > > Unable to handle kernel paging request at virtual address ffff000008e460d8 > pgd = ffff800003504000 > [ffff000008e460d8] *pgd=0000000083473003, *pud=0000000083503003, *pmd=0000000000000000 > Internal error: Oops: 9600004f [#1] PREEMPT SMP > > we'll see: > > Unable to handle kernel write to read-only memory at virtual address ffff000008e760d8 > pgd = ffff80003d3de000 > [ffff000008e760d8] *pgd=0000000083472003, *pud=0000000083435003, *pmd=0000000000000000 > Internal error: Oops: 9600004f [#1] PREEMPT SMP > > We also fold the userspace address check into is_permission_fault() > instead of at the current callsite so that the function can't be > abused with software PAN and a kernel space address. > > Cc: James Morse > Cc: Laura Abbott > Cc: Mark Rutland > Signed-off-by: Stephen Boyd Acked-by: Laura Abbott > --- > > Changes from v2: > * Fold addr check into is_permission_fault() (James Morse) > > Changes from v1: > * Move into __do_kernel_fault() (Mark Rutland) > > arch/arm64/mm/fault.c | 54 +++++++++++++++++++++++++++++++++------------------ > 1 file changed, 35 insertions(+), 19 deletions(-) > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > index 156169c6981b..c6560cb4ef50 100644 > --- a/arch/arm64/mm/fault.c > +++ b/arch/arm64/mm/fault.c > @@ -160,12 +160,32 @@ static bool is_el1_instruction_abort(unsigned int esr) > return ESR_ELx_EC(esr) == ESR_ELx_EC_IABT_CUR; > } > > +static inline bool is_permission_fault(unsigned int esr, struct pt_regs *regs, > + unsigned long addr) > +{ > + unsigned int ec = ESR_ELx_EC(esr); > + unsigned int fsc_type = esr & ESR_ELx_FSC_TYPE; > + > + if (ec != ESR_ELx_EC_DABT_CUR && ec != ESR_ELx_EC_IABT_CUR) > + return false; > + > + if (fsc_type == ESR_ELx_FSC_PERM) > + return true; > + > + if (addr < USER_DS && system_uses_ttbr0_pan()) > + return fsc_type == ESR_ELx_FSC_FAULT && > + (regs->pstate & PSR_PAN_BIT); > + > + return false; > +} > + > /* > * The kernel tried to access some page that wasn't present. > */ > static void __do_kernel_fault(struct mm_struct *mm, unsigned long addr, > unsigned int esr, struct pt_regs *regs) > { > + const char *msg; > /* > * Are we prepared to handle this kernel fault? > * We are almost certainly not prepared to handle instruction faults. > @@ -177,9 +197,20 @@ static void __do_kernel_fault(struct mm_struct *mm, unsigned long addr, > * No handler, we'll have to terminate things with extreme prejudice. > */ > bust_spinlocks(1); > - pr_alert("Unable to handle kernel %s at virtual address %08lx\n", > - (addr < PAGE_SIZE) ? "NULL pointer dereference" : > - "paging request", addr); > + > + if (is_permission_fault(esr, regs, addr)) { > + if (esr & ESR_ELx_WNR) > + msg = "write to read-only memory"; > + else > + msg = "read from unreadable memory"; > + } else if (addr < PAGE_SIZE) { > + msg = "NULL pointer dereference"; > + } else { > + msg = "paging request"; > + } > + > + pr_alert("Unable to handle kernel %s at virtual address %08lx\n", msg, > + addr); > > show_pte(mm, addr); > die("Oops", regs, esr); > @@ -269,21 +300,6 @@ static int __do_page_fault(struct mm_struct *mm, unsigned long addr, > return fault; > } > > -static inline bool is_permission_fault(unsigned int esr, struct pt_regs *regs) > -{ > - unsigned int ec = ESR_ELx_EC(esr); > - unsigned int fsc_type = esr & ESR_ELx_FSC_TYPE; > - > - if (ec != ESR_ELx_EC_DABT_CUR && ec != ESR_ELx_EC_IABT_CUR) > - return false; > - > - if (system_uses_ttbr0_pan()) > - return fsc_type == ESR_ELx_FSC_FAULT && > - (regs->pstate & PSR_PAN_BIT); > - else > - return fsc_type == ESR_ELx_FSC_PERM; > -} > - > static bool is_el0_instruction_abort(unsigned int esr) > { > return ESR_ELx_EC(esr) == ESR_ELx_EC_IABT_LOW; > @@ -321,7 +337,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, > mm_flags |= FAULT_FLAG_WRITE; > } > > - if (addr < USER_DS && is_permission_fault(esr, regs)) { > + if (is_permission_fault(esr, regs, addr)) { > /* regs->orig_addr_limit may be 0 if we entered from EL0 */ > if (regs->orig_addr_limit == KERNEL_DS) > die("Accessing user space memory with fs=KERNEL_DS", regs, esr); >