On Mon, Jun 01, 2009 at 08:37:31PM -0400, Masami Hiramatsu wrote: > 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 <[email protected]> > Cc: Ananth N Mavinakayanahalli <[email protected]> > Cc: Jim Keniston <[email protected]> > Cc: Ingo Molnar <[email protected]>
Acked-by: Ananth N Mavinakayanahalli <[email protected]> > --- > > 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 7b5169d..41d524f 100644 > --- a/arch/x86/kernel/kprobes.c > +++ b/arch/x86/kernel/kprobes.c > @@ -48,12 +48,14 @@ > #include <linux/preempt.h> > #include <linux/module.h> > #include <linux/kdebug.h> > +#include <linux/kallsyms.h> > > #include <asm/cacheflush.h> > #include <asm/desc.h> > #include <asm/pgtable.h> > #include <asm/uaccess.h> > #include <asm/alternative.h> > +#include <asm/insn.h> > > void jprobe_return_end(void); > > @@ -244,6 +246,71 @@ 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. > */ > @@ -359,6 +426,8 @@ 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: [email protected] -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
