From mboxrd@z Thu Jan 1 00:00:00 1970 From: Masami Hiramatsu Subject: [PATCH -tip -v11 03/11] kprobes: checks probe address is instruction boudary on x86 Date: Thu, 09 Jul 2009 16:22:41 -0400 Message-ID: <20090709202241.13223.11317.stgit@localhost.localdomain> References: <20090709202220.13223.97114.stgit@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: systemtap , kvm , DLE , Masami Hiramatsu , Ananth N Mavinakayanahalli , Jim Keniston , Ingo Molnar To: Ingo Molnar , Steven Rostedt , lkml Return-path: Received: from mx2.redhat.com ([66.187.237.31]:41266 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753219AbZGIUT4 (ORCPT ); Thu, 9 Jul 2009 16:19:56 -0400 In-Reply-To: <20090709202220.13223.97114.stgit@localhost.localdomain> Sender: kvm-owner@vger.kernel.org List-ID: 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