From mboxrd@z Thu Jan 1 00:00:00 1970 From: Masami Hiramatsu Subject: [PATCH -tip v5 2/7] kprobes: checks probe address is instruction boudary on x86 Date: Fri, 08 May 2009 20:48:47 -0400 Message-ID: <20090509004847.5505.37957.stgit@localhost.localdomain> References: <20090509004829.5505.38720.stgit@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: systemtap, kvm, Masami Hiramatsu , Ananth N Mavinakayanahalli , Jim Keniston , Ingo Molnar To: Ingo Molnar, Steven Rostedt , lkml Return-path: In-Reply-To: <20090509004829.5505.38720.stgit@localhost.localdomain> List-Unsubscribe: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org List-Id: kvm.vger.kernel.org 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 Cc: Ananth N Mavinakayanahalli Cc: Jim Keniston Cc: Ingo Molnar --- arch/x86/kernel/kprobes.c | 54 +++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 54 insertions(+), 0 deletions(-) diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c index 7b5169d..3d5e85f 100644 --- a/arch/x86/kernel/kprobes.c +++ b/arch/x86/kernel/kprobes.c @@ -48,12 +48,14 @@ #include #include #include +#include #include #include #include #include #include +#include void jprobe_return_end(void); @@ -244,6 +246,56 @@ 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; + + /* + * Don't use p->ainsn.insn, which could be modified -- e.g., + * by fix_riprel(). + */ + 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]; + + /* Lookup symbol including addr */ + if (!kallsyms_lookup(paddr, NULL, &offset, NULL, __dummy_buf)) + return 0; + + /* Decode instructions */ + addr = paddr - offset; + while (addr < paddr) { + insn_init_kernel(&insn, (void *)addr); + insn_get_opcode(&insn); + if (OPCODE1(&insn) == BREAKPOINT_INSTRUCTION) { + ret = recover_probed_instruction(buf, addr); + if (ret) + return 0; + insn_init_kernel(&insn, buf); + } + insn_get_length(&insn); + addr += insn.length; + } + + return (addr == paddr); +} + /* * Returns non-zero if opcode modifies the interrupt flag. */ @@ -359,6 +411,8 @@ 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