From patchwork Tue Aug 7 15:49:47 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Will Deacon X-Patchwork-Id: 1286501 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork2.kernel.org Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) by patchwork2.kernel.org (Postfix) with ESMTP id 87C1EDF280 for ; Tue, 7 Aug 2012 15:54:05 +0000 (UTC) Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.76 #1 (Red Hat Linux)) id 1Sym2q-00075E-N1; Tue, 07 Aug 2012 15:50:08 +0000 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]) by merlin.infradead.org with esmtp (Exim 4.76 #1 (Red Hat Linux)) id 1Sym2d-00072D-Pi for linux-arm-kernel@lists.infradead.org; Tue, 07 Aug 2012 15:49:57 +0000 Received: from mudshark.cambridge.arm.com (mudshark.cambridge.arm.com [10.1.79.58]) by cam-admin0.cambridge.arm.com (8.12.6/8.12.6) with ESMTP id q77FnoOK003536; Tue, 7 Aug 2012 16:49:50 +0100 (BST) Received: by mudshark.cambridge.arm.com (Postfix, from userid 1000) id D40A7C2A8D; Tue, 7 Aug 2012 16:49:49 +0100 (BST) From: Will Deacon To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 1/2] ARM: hw_breakpoint: don't rely on dfsr to show watchpoint access type Date: Tue, 7 Aug 2012 16:49:47 +0100 Message-Id: <1344354588-28153-1-git-send-email-will.deacon@arm.com> X-Mailer: git-send-email 1.7.4.1 X-Spam-Note: CRM114 invocation failed X-Spam-Score: -6.9 (------) X-Spam-Report: SpamAssassin version 3.3.2 on merlin.infradead.org summary: Content analysis details: (-6.9 points) pts rule name description ---- ---------------------- -------------------------------------------------- -5.0 RCVD_IN_DNSWL_HI RBL: Sender listed at http://www.dnswl.org/, high trust [217.140.96.50 listed in list.dnswl.org] -0.0 T_RP_MATCHES_RCVD Envelope sender domain matches handover relay domain -0.0 SPF_PASS SPF: sender matches SPF record -1.9 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Cc: Will Deacon X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: linux-arm-kernel-bounces@lists.infradead.org Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org From ARM debug architecture v7.1 onwards, a watchpoint exception causes the DFAR to be updated with the faulting data address. However, DFSR.WnR takes an UNKNOWN value and therefore cannot be used in general to determine the access type that triggered the watchpoint. This patch forbids watchpoints without an overflow handler from specifying a specific access type (load/store). Those with overflow handlers must be able to handle false positives potentially triggered by a watchpoint of a different access type on the same address. For SIGTRAP-based handlers (i.e. ptrace), this should have no impact. Signed-off-by: Will Deacon --- arch/arm/kernel/hw_breakpoint.c | 54 ++++++++++++++++++++++++++++----------- 1 files changed, 39 insertions(+), 15 deletions(-) diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c index ba386bd..418d980 100644 --- a/arch/arm/kernel/hw_breakpoint.c +++ b/arch/arm/kernel/hw_breakpoint.c @@ -159,6 +159,12 @@ static int debug_arch_supported(void) arch >= ARM_DEBUG_ARCH_V7_1; } +/* Can we determine the watchpoint access type from the fsr? */ +static int debug_exception_updates_fsr(void) +{ + return 0; +} + /* Determine number of WRP registers available. */ static int get_num_wrp_resources(void) { @@ -619,18 +625,34 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp) info->address &= ~alignment_mask; info->ctrl.len <<= offset; - /* - * Currently we rely on an overflow handler to take - * care of single-stepping the breakpoint when it fires. - * In the case of userspace breakpoints on a core with V7 debug, - * we can use the mismatch feature as a poor-man's hardware - * single-step, but this only works for per-task breakpoints. - */ - if (!bp->overflow_handler && (arch_check_bp_in_kernelspace(bp) || - !core_has_mismatch_brps() || !bp->hw.bp_target)) { - pr_warning("overflow handler required but none found\n"); - ret = -EINVAL; + if (!bp->overflow_handler) { + /* + * Mismatch breakpoints are required for single-stepping + * breakpoints. + */ + if (!core_has_mismatch_brps()) + return -EINVAL; + + /* We don't allow mismatch breakpoints in kernel space. */ + if (arch_check_bp_in_kernelspace(bp)) + return -EPERM; + + /* + * Per-cpu breakpoints are not supported by our stepping + * mechanism. */ + if (!bp->hw.bp_target) + return -EINVAL; + + /* + * We only support specific access types if the fsr + * reports them. + */ + if (!debug_exception_updates_fsr() && + (info->ctrl.type == ARM_BREAKPOINT_LOAD || + info->ctrl.type == ARM_BREAKPOINT_STORE)) + return -EINVAL; } + out: return ret; } @@ -706,10 +728,12 @@ static void watchpoint_handler(unsigned long addr, unsigned int fsr, goto unlock; /* Check that the access type matches. */ - access = (fsr & ARM_FSR_ACCESS_MASK) ? HW_BREAKPOINT_W : - HW_BREAKPOINT_R; - if (!(access & hw_breakpoint_type(wp))) - goto unlock; + if (debug_exception_updates_fsr()) { + access = (fsr & ARM_FSR_ACCESS_MASK) ? + HW_BREAKPOINT_W : HW_BREAKPOINT_R; + if (!(access & hw_breakpoint_type(wp))) + goto unlock; + } /* We have a winner. */ info->trigger = addr;