From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752038AbcIGOOg (ORCPT ); Wed, 7 Sep 2016 10:14:36 -0400 Received: from mail-qk0-f177.google.com ([209.85.220.177]:35741 "EHLO mail-qk0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750842AbcIGOOe (ORCPT ); Wed, 7 Sep 2016 10:14:34 -0400 Subject: Re: [PATCH v2] arm64: Improve kprobes test for atomic sequence To: Masami Hiramatsu References: <1473184499-6018-1-git-send-email-dave.long@linaro.org> <20160907145244.ea997984134c15c12793ca74@kernel.org> 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 From: David Long Message-ID: <57D0203E.1070901@linaro.org> Date: Wed, 7 Sep 2016 10:12:14 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <20160907145244.ea997984134c15c12793ca74@kernel.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? > 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