From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755968AbcIHCJe (ORCPT ); Wed, 7 Sep 2016 22:09:34 -0400 Received: from mail.kernel.org ([198.145.29.136]:47920 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751176AbcIHCJ0 (ORCPT ); Wed, 7 Sep 2016 22:09:26 -0400 Date: Thu, 8 Sep 2016 11:09:20 +0900 From: Masami Hiramatsu To: David Long Cc: Ananth N Mavinakayanahalli , Anil S Keshavamurthy , "David S. Miller" , Will Deacon , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, Sandeepa Prabhu , William Cohen , Pratyush Anand , Mark Brown Subject: Re: [PATCH v2] arm64: Improve kprobes test for atomic sequence Message-Id: <20160908110920.f618f545ee75669cee373fdf@kernel.org> In-Reply-To: <57D0203E.1070901@linaro.org> References: <1473184499-6018-1-git-send-email-dave.long@linaro.org> <20160907145244.ea997984134c15c12793ca74@kernel.org> <57D0203E.1070901@linaro.org> X-Mailer: Sylpheed 3.5.0 (GTK+ 2.24.30; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 7 Sep 2016 10:12:14 -0400 David Long wrote: > On 09/07/2016 01:52 AM, Masami Hiramatsu wrote: > > On Tue, 6 Sep 2016 13:54:59 -0400 > > David Long wrote: > > > >> From: "David A. Long" > >> > >> Kprobes searches backwards a finite number of instructions to determine if > >> there is an attempt to probe a load/store exclusive sequence. It stops when > >> it hits the maximum number of instructions or a load or store exclusive. > >> However this means it can run up past the beginning of the function and > >> start looking at literal constants. This has been shown to cause a false > >> positive and blocks insertion of the probe. To fix this, further limit the > >> backwards search to stop if it hits a symbol address from kallsyms. The > >> presumption is that this is the entry point to this code (particularly for > >> the common case of placing probes at the beginning of functions). > >> > >> This also improves efficiency by not searching code that is not part of the > >> function. There may be some possibility that the label might not denote the > >> entry path to the probed instruction but the likelihood seems low and this > >> is just another example of how the kprobes user really needs to be > >> careful about what they are doing. > > > > Hi Dave, > > > > kallsyms_lookup_size_offset() part looks good to me. By the way, > > is there any reason we'll check the _text and module's base address > > boundary? > > I think those are already searced by kallsyms_lookup_size_offset(), > > so you don't need to check those. If the address is not found by > > kallsyms_lookup_size_offset(), that address maybe out-of-text. > > > > CONFIG KPROBES does currently select CONFIG_KALLSYMS, but is it wise for > this code to depend on that? Perhaps the text boundary checking should > be moved under an else clause for the case of > kallsyms_lookup_size_offset() failing? Would you have any case where the address is in kernel_text but kallsyms_lookup failed to find symbol? IMHO, even if there is, we should reject probing on such "nowhere" address. Thank you, > > > Thank you, > >> > >> Signed-off-by: David A. Long > >> --- > >> arch/arm64/kernel/probes/decode-insn.c | 48 +++++++++++++++++++++++----------- > >> 1 file changed, 33 insertions(+), 15 deletions(-) > >> > >> diff --git a/arch/arm64/kernel/probes/decode-insn.c b/arch/arm64/kernel/probes/decode-insn.c > >> index 37e47a9..356ee52 100644 > >> --- a/arch/arm64/kernel/probes/decode-insn.c > >> +++ b/arch/arm64/kernel/probes/decode-insn.c > >> @@ -16,6 +16,7 @@ > >> #include > >> #include > >> #include > >> +#include > >> #include > >> #include > >> #include > >> @@ -122,7 +123,7 @@ arm_probe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi) > >> static bool __kprobes > >> is_probed_address_atomic(kprobe_opcode_t *scan_start, kprobe_opcode_t *scan_end) > >> { > >> - while (scan_start > scan_end) { > >> + while (scan_start >= scan_end) { > >> /* > >> * atomic region starts from exclusive load and ends with > >> * exclusive store. > >> @@ -144,26 +145,43 @@ arm_kprobe_decode_insn(kprobe_opcode_t *addr, struct arch_specific_insn *asi) > >> kprobe_opcode_t insn = le32_to_cpu(*addr); > >> kprobe_opcode_t *scan_start = addr - 1; > >> kprobe_opcode_t *scan_end = addr - MAX_ATOMIC_CONTEXT_SIZE; > >> + unsigned long size = 0, offset = 0; > >> #if defined(CONFIG_MODULES) && defined(MODULES_VADDR) > >> struct module *mod; > >> #endif > >> > >> - if (addr >= (kprobe_opcode_t *)_text && > >> - scan_end < (kprobe_opcode_t *)_text) > >> - scan_end = (kprobe_opcode_t *)_text; > >> + /* > >> + * If there's a symbol defined in front of and near enough to > >> + * the probe address assume it is the entry point to this > >> + * code and use it to further limit how far back we search > >> + * when determining if we're in an atomic sequence. > >> + */ > >> + if (kallsyms_lookup_size_offset((unsigned long) addr, &size, &offset)) > >> + if (offset < (MAX_ATOMIC_CONTEXT_SIZE*sizeof(kprobe_opcode_t))) > >> + scan_end = addr - (offset / sizeof(kprobe_opcode_t)); > >> + > >> + if (scan_end <= scan_start) { > >> + if (addr >= (kprobe_opcode_t *)_text && > >> + scan_end < (kprobe_opcode_t *)_text) > >> + scan_end = (kprobe_opcode_t *)_text; > >> #if defined(CONFIG_MODULES) && defined(MODULES_VADDR) > >> - else { > >> - preempt_disable(); > >> - mod = __module_address((unsigned long)addr); > >> - if (mod && within_module_init((unsigned long)addr, mod) && > >> - !within_module_init((unsigned long)scan_end, mod)) > >> - scan_end = (kprobe_opcode_t *)mod->init_layout.base; > >> - else if (mod && within_module_core((unsigned long)addr, mod) && > >> - !within_module_core((unsigned long)scan_end, mod)) > >> - scan_end = (kprobe_opcode_t *)mod->core_layout.base; > >> - preempt_enable(); > >> - } > >> + else { > >> + preempt_disable(); > >> + mod = __module_address((unsigned long)addr); > >> + if (mod && > >> + within_module_init((unsigned long)addr, mod) && > >> + !within_module_init((unsigned long)scan_end, mod)) > >> + scan_end = > >> + (kprobe_opcode_t *)mod->init_layout.base; > >> + else if (mod && > >> + within_module_core((unsigned long)addr, mod) && > >> + !within_module_core((unsigned long)scan_end, mod)) > >> + scan_end = > >> + (kprobe_opcode_t *)mod->core_layout.base; > >> + preempt_enable(); > >> + } > >> #endif > >> + } > >> decoded = arm_probe_decode_insn(insn, asi); > >> > >> if (decoded == INSN_REJECTED || > >> -- > >> 2.5.0 > >> > > Thanks, > -dl > > -- Masami Hiramatsu