Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763935AbZGABZd (ORCPT ); Tue, 30 Jun 2009 21:25:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1762097AbZGABHR (ORCPT ); Tue, 30 Jun 2009 21:07:17 -0400 Received: from mx2.redhat.com ([66.187.237.31]:36525 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763959AbZGABHG (ORCPT ); Tue, 30 Jun 2009 21:07:06 -0400 From: Masami Hiramatsu Subject: [PATCH -tip -v10 3/7] kprobes: checks probe address is instruction boudary on x86 To: Ingo Molnar , Steven Rostedt , lkml Cc: systemtap , kvm , DLE , Masami Hiramatsu , Ananth N Mavinakayanahalli , Jim Keniston , Ingo Molnar Date: Tue, 30 Jun 2009 21:09:00 -0400 Message-ID: <20090701010900.32547.263.stgit@localhost.localdomain> In-Reply-To: <20090701010838.32547.62843.stgit@localhost.localdomain> References: <20090701010838.32547.62843.stgit@localhost.localdomain> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3745 Lines: 129 Ensure safeness of inserting kprobes by checking whether the specified address is at the first byte of a instruction on x86. This is done by decoding probed function from its head to the probe point. Signed-off-by: Masami Hiramatsu Acked-by: Ananth N Mavinakayanahalli Cc: Jim Keniston Cc: Ingo Molnar --- arch/x86/kernel/kprobes.c | 69 +++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 69 insertions(+), 0 deletions(-) diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c index b5b1848..5341842 100644 --- a/arch/x86/kernel/kprobes.c +++ b/arch/x86/kernel/kprobes.c @@ -48,6 +48,7 @@ #include #include #include +#include #include #include @@ -55,6 +56,7 @@ #include #include #include +#include void jprobe_return_end(void); @@ -245,6 +247,71 @@ retry: } } +/* Recover the probed instruction at addr for further analysis. */ +static int recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr) +{ + struct kprobe *kp; + kp = get_kprobe((void *)addr); + if (!kp) + return -EINVAL; + + /* + * Basically, kp->ainsn.insn has an original instruction. + * However, RIP-relative instruction can not do single-stepping + * at different place, fix_riprel() tweaks the displacement of + * that instruction. In that case, we can't recover the instruction + * from the kp->ainsn.insn. + * + * On the other hand, kp->opcode has a copy of the first byte of + * the probed instruction, which is overwritten by int3. And + * the instruction at kp->addr is not modified by kprobes except + * for the first byte, we can recover the original instruction + * from it and kp->opcode. + */ + memcpy(buf, kp->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t)); + buf[0] = kp->opcode; + return 0; +} + +/* Dummy buffers for kallsyms_lookup */ +static char __dummy_buf[KSYM_NAME_LEN]; + +/* Check if paddr is at an instruction boundary */ +static int __kprobes can_probe(unsigned long paddr) +{ + int ret; + unsigned long addr, offset = 0; + struct insn insn; + kprobe_opcode_t buf[MAX_INSN_SIZE]; + + if (!kallsyms_lookup(paddr, NULL, &offset, NULL, __dummy_buf)) + return 0; + + /* Decode instructions */ + addr = paddr - offset; + while (addr < paddr) { + kernel_insn_init(&insn, (void *)addr); + insn_get_opcode(&insn); + + /* Check if the instruction has been modified. */ + if (OPCODE1(&insn) == BREAKPOINT_INSTRUCTION) { + ret = recover_probed_instruction(buf, addr); + if (ret) + /* + * Another debugging subsystem might insert + * this breakpoint. In that case, we can't + * recover it. + */ + return 0; + kernel_insn_init(&insn, buf); + } + insn_get_length(&insn); + addr += insn.length; + } + + return (addr == paddr); +} + /* * Returns non-zero if opcode modifies the interrupt flag. */ @@ -360,6 +427,8 @@ static void __kprobes arch_copy_kprobe(struct kprobe *p) int __kprobes arch_prepare_kprobe(struct kprobe *p) { + if (!can_probe((unsigned long)p->addr)) + return -EILSEQ; /* insn: must be on special executable page on x86. */ p->ainsn.insn = get_insn_slot(); if (!p->ainsn.insn) -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division e-mail: mhiramat@redhat.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/