From 802eae7c800fb7f583e6c06afa363585af2bef00 Mon Sep 17 00:00:00 2001 From: Rusty Lynch Date: Mon, 27 Jun 2005 15:17:08 -0700 Subject: [PATCH] Return probe redesign: architecture independent changes The following is the second version of the function return probe patches I sent out earlier this week. Changes since my last submission include: * Fix in ppc64 code removing an unneeded call to re-enable preemption * Fix a build problem in ia64 when kprobes was turned off * Added another BUG_ON check to each of the architecture trampoline handlers My initial patch description ==> From my experiences with adding return probes to x86_64 and ia64, and the feedback on LKML to those patches, I think we can simplify the design for return probes. The following patch tweaks the original design such that: * Instead of storing the stack address in the return probe instance, the task pointer is stored. This gives us all we need in order to: - find the correct return probe instance when we enter the trampoline (even if we are recursing) - find all left-over return probe instances when the task is going away This has the side effect of simplifying the implementation since more work can be done in kernel/kprobes.c since architecture specific knowledge of the stack layout is no longer required. Specifically, we no longer have: - arch_get_kprobe_task() - arch_kprobe_flush_task() - get_rp_inst_tsk() - get_rp_inst() - trampoline_post_handler() * Instead of splitting the return probe handling and cleanup logic across the pre and post trampoline handlers, all the work is pushed into the pre function (trampoline_probe_handler), and then we skip single stepping the original function. In this case the original instruction to be single stepped was just a NOP, and we can do without the extra interruption. The new flow of events to having a return probe handler execute when a target function exits is: * At system initialization time, a kprobe is inserted at the beginning of kretprobe_trampoline. kernel/kprobes.c use to handle this on it's own, but ia64 needed to do this a little differently (i.e. a function pointer is really a pointer to a structure containing the instruction pointer and a global pointer), so I added the notion of arch_init(), so that kernel/kprobes.c:init_kprobes() now allows architecture specific initialization by calling arch_init() before exiting. Each architecture now registers a kprobe on it's own trampoline function. * register_kretprobe() will insert a kprobe at the beginning of the targeted function with the kprobe pre_handler set to arch_prepare_kretprobe (still no change) * When the target function is entered, the kprobe is fired, calling arch_prepare_kretprobe (still no change) * In arch_prepare_kretprobe() we try to get a free instance and if one is available then we fill out the instance with a pointer to the return probe, the original return address, and a pointer to the task structure (instead of the stack address.) Just like before we change the return address to the trampoline function and mark the instance as used. If multiple return probes are registered for a given target function, then arch_prepare_kretprobe() will get called multiple times for the same task (since our kprobe implementation is able to handle multiple kprobes at the same address.) Past the first call to arch_prepare_kretprobe, we end up with the original address stored in the return probe instance pointing to our trampoline function. (This is a significant difference from the original arch_prepare_kretprobe design.) * Target function executes like normal and then returns to kretprobe_trampoline. * kprobe inserted on the first instruction of kretprobe_trampoline is fired and calls trampoline_probe_handler() (no change here) * trampoline_probe_handler() consumes each of the instances associated with the current task by calling the registered handler function and marking the instance as unused until an instance is found that has a return address different then the trampoline function. (change similar to my previous ia64 RFC) * If the task is killed with some left-over return probe instances (meaning that a target function was entered, but never returned), then we just free any instances associated with the task. (Not much different other then we can handle this without calling architecture specific functions.) There is a known problem that this patch does not yet solve where registering a return probe flush_old_exec or flush_thread will put us in a bad state. Most likely the best way to handle this is to not allow registering return probes on these two functions. (Significant change) This patch series applies to the 2.6.12-rc6-mm1 kernel, and provides: * kernel/kprobes.c changes * i386 patch of existing return probes implementation * x86_64 patch of existing return probe implementation * ia64 implementation * ppc64 implementation (provided by Ananth) This patch implements the architecture independant changes for a reworking of the kprobes based function return probes design. Changes include: * Removing functions for querying a return probe instance off a stack address * Removing the stack_addr field from the kretprobe_instance definition, and adding a task pointer * Adding architecture specific initialization via arch_init() * Removing extern definitions for the architecture trampoline functions (this isn't needed anymore since the architecture handles the initialization of the kprobe in the return probe trampoline function.) Signed-off-by: Rusty Lynch Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/kprobes.c | 69 ++++++++++++++++---------------------------------------- 1 file changed, 19 insertions(+), 50 deletions(-) (limited to 'kernel/kprobes.c') diff --git a/kernel/kprobes.c b/kernel/kprobes.c index 65242529a75..90c0e82b650 100644 --- a/kernel/kprobes.c +++ b/kernel/kprobes.c @@ -240,12 +240,6 @@ static int aggr_break_handler(struct kprobe *p, struct pt_regs *regs) return 0; } -struct kprobe trampoline_p = { - .addr = (kprobe_opcode_t *) &kretprobe_trampoline, - .pre_handler = trampoline_probe_handler, - .post_handler = trampoline_post_handler -}; - struct kretprobe_instance *get_free_rp_inst(struct kretprobe *rp) { struct hlist_node *node; @@ -264,35 +258,18 @@ static struct kretprobe_instance *get_used_rp_inst(struct kretprobe *rp) return NULL; } -struct kretprobe_instance *get_rp_inst(void *sara) -{ - struct hlist_head *head; - struct hlist_node *node; - struct task_struct *tsk; - struct kretprobe_instance *ri; - - tsk = arch_get_kprobe_task(sara); - head = &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)]; - hlist_for_each_entry(ri, node, head, hlist) { - if (ri->stack_addr == sara) - return ri; - } - return NULL; -} - void add_rp_inst(struct kretprobe_instance *ri) { - struct task_struct *tsk; /* * Remove rp inst off the free list - * Add it back when probed function returns */ hlist_del(&ri->uflist); - tsk = arch_get_kprobe_task(ri->stack_addr); + /* Add rp inst onto table */ INIT_HLIST_NODE(&ri->hlist); hlist_add_head(&ri->hlist, - &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)]); + &kretprobe_inst_table[hash_ptr(ri->task, KPROBE_HASH_BITS)]); /* Also add this rp inst to the used list. */ INIT_HLIST_NODE(&ri->uflist); @@ -319,34 +296,25 @@ struct hlist_head * kretprobe_inst_table_head(struct task_struct *tsk) return &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)]; } -struct kretprobe_instance *get_rp_inst_tsk(struct task_struct *tk) -{ - struct task_struct *tsk; - struct hlist_head *head; - struct hlist_node *node; - struct kretprobe_instance *ri; - - head = &kretprobe_inst_table[hash_ptr(tk, KPROBE_HASH_BITS)]; - - hlist_for_each_entry(ri, node, head, hlist) { - tsk = arch_get_kprobe_task(ri->stack_addr); - if (tsk == tk) - return ri; - } - return NULL; -} - /* - * This function is called from do_exit or do_execv when task tk's stack is - * about to be recycled. Recycle any function-return probe instances - * associated with this task. These represent probed functions that have - * been called but may never return. + * This function is called from exit_thread or flush_thread when task tk's + * stack is being recycled so that we can recycle any function-return probe + * instances associated with this task. These left over instances represent + * probed functions that have been called but will never return. */ void kprobe_flush_task(struct task_struct *tk) { + struct kretprobe_instance *ri; + struct hlist_head *head; + struct hlist_node *node, *tmp; unsigned long flags = 0; + spin_lock_irqsave(&kprobe_lock, flags); - arch_kprobe_flush_task(tk); + head = kretprobe_inst_table_head(current); + hlist_for_each_entry_safe(ri, node, tmp, head, hlist) { + if (ri->task == tk) + recycle_rp_inst(ri); + } spin_unlock_irqrestore(&kprobe_lock, flags); } @@ -606,9 +574,10 @@ static int __init init_kprobes(void) INIT_HLIST_HEAD(&kretprobe_inst_table[i]); } - err = register_die_notifier(&kprobe_exceptions_nb); - /* Register the trampoline probe for return probe */ - register_kprobe(&trampoline_p); + err = arch_init(); + if (!err) + err = register_die_notifier(&kprobe_exceptions_nb); + return err; } -- cgit v1.2.3-18-g5258