Messages in this thread Patch in this message | | | Date | Mon, 28 Mar 2005 21:34:08 -0500 | From | Ananth N Mavinakayanahalli <> | Subject | Re: kprobe_handler should check pre_handler function |
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On Mon, Mar 28, 2005 at 04:10:32PM -0500, William Cohen wrote:
Hi Will,
> I found kprobes expects there to be a pre_handler function in the > structure. I was writing a probe that only needed a post_handler > function, no pre_handler function. The probe was tracking the > destinations of indirect calls and jumps, the probe needs to fire after > the instruction single steps to get the target address. The probe > crashed the machine because arch/i386/kernel/kprobe.c:kprobe_handler() > blindly calls p->pre_handler(). There should be a check to verify that > the pointer is non-null. There are cases where the pre_handler is not > needed and it would make sense to set it to NULL. Thus, a check should > be done for pre_handler like post_handler and fault_handler.
You are right. The check for pre_handler is needed and here is a patch against 2.6.12-rc1-mm3 that does this.
Thanks, Ananth
Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
diff -Narup temp/linux-2.6.12-rc1/arch/i386/kernel/kprobes.c linux-2.6.12-rc1/arch/i386/kernel/kprobes.c --- temp/linux-2.6.12-rc1/arch/i386/kernel/kprobes.c 2005-03-17 20:34:10.000000000 -0500 +++ linux-2.6.12-rc1/arch/i386/kernel/kprobes.c 2005-03-28 17:51:21.000000000 -0500 @@ -159,17 +159,16 @@ static int kprobe_handler(struct pt_regs if (is_IF_modifier(p->opcode)) kprobe_saved_eflags &= ~IF_MASK; - if (p->pre_handler(p, regs)) { + if (p->pre_handler && p->pre_handler(p, regs)) /* handler has already set things up, so skip ss setup */ return 1; - } - ss_probe: +ss_probe: prepare_singlestep(p, regs); kprobe_status = KPROBE_HIT_SS; return 1; - no_kprobe: +no_kprobe: preempt_enable_no_resched(); return ret; } diff -Narup temp/linux-2.6.12-rc1/arch/ppc64/kernel/kprobes.c linux-2.6.12-rc1/arch/ppc64/kernel/kprobes.c --- temp/linux-2.6.12-rc1/arch/ppc64/kernel/kprobes.c 2005-03-28 17:48:56.000000000 -0500 +++ linux-2.6.12-rc1/arch/ppc64/kernel/kprobes.c 2005-03-28 17:51:31.000000000 -0500 @@ -128,10 +128,9 @@ static inline int kprobe_handler(struct kprobe_status = KPROBE_HIT_ACTIVE; current_kprobe = p; kprobe_saved_msr = regs->msr; - if (p->pre_handler(p, regs)) { + if (p->pre_handler && p->pre_handler(p, regs)) /* handler has already set things up, so skip ss setup */ return 1; - } ss_probe: prepare_singlestep(p, regs); diff -Narup temp/linux-2.6.12-rc1/arch/sparc64/kernel/kprobes.c linux-2.6.12-rc1/arch/sparc64/kernel/kprobes.c --- temp/linux-2.6.12-rc1/arch/sparc64/kernel/kprobes.c 2005-03-17 20:34:33.000000000 -0500 +++ linux-2.6.12-rc1/arch/sparc64/kernel/kprobes.c 2005-03-28 17:50:55.000000000 -0500 @@ -128,7 +128,7 @@ static int kprobe_handler(struct pt_regs kprobe_status = KPROBE_HIT_ACTIVE; current_kprobe = p; - if (p->pre_handler(p, regs)) + if (p->pre_handler && p->pre_handler(p, regs)) return 1; ss_probe: diff -Narup temp/linux-2.6.12-rc1/arch/x86_64/kernel/kprobes.c linux-2.6.12-rc1/arch/x86_64/kernel/kprobes.c --- temp/linux-2.6.12-rc1/arch/x86_64/kernel/kprobes.c 2005-03-28 17:48:57.000000000 -0500 +++ linux-2.6.12-rc1/arch/x86_64/kernel/kprobes.c 2005-03-28 17:51:10.000000000 -0500 @@ -293,17 +293,16 @@ int kprobe_handler(struct pt_regs *regs) if (is_IF_modifier(p->ainsn.insn)) kprobe_saved_rflags &= ~IF_MASK; - if (p->pre_handler(p, regs)) { + if (p->pre_handler && p->pre_handler(p, regs)) /* handler has already set things up, so skip ss setup */ return 1; - } - ss_probe: +ss_probe: prepare_singlestep(p, regs); kprobe_status = KPROBE_HIT_SS; return 1; - no_kprobe: +no_kprobe: preempt_enable_no_resched(); return ret; } - 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/
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