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authorRusty Lynch <rusty.lynch@intel.com>2005-06-23 00:09:23 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-06-23 09:45:21 -0700
commit73649dab0fd524cb8545a8cb83c6eaf77b107105 (patch)
tree70f43b37ba915de148c28008e275dacec200e33f /arch
parentb94cce926b2b902b79380ccba370d6f9f2980de0 (diff)
[PATCH] x86_64 specific function return probes
The following patch adds the x86_64 architecture specific implementation for function return probes. Function return probes is a mechanism built on top of kprobes that allows a caller to register a handler to be called when a given function exits. For example, to instrument the return path of sys_mkdir: static int sys_mkdir_exit(struct kretprobe_instance *i, struct pt_regs *regs) { printk("sys_mkdir exited\n"); return 0; } static struct kretprobe return_probe = { .handler = sys_mkdir_exit, }; <inside setup function> return_probe.kp.addr = (kprobe_opcode_t *) kallsyms_lookup_name("sys_mkdir"); if (register_kretprobe(&return_probe)) { printk(KERN_DEBUG "Unable to register return probe!\n"); /* do error path */ } <inside cleanup function> unregister_kretprobe(&return_probe); The way this works is that: * At system initialization time, kernel/kprobes.c installs a kprobe on a function called kretprobe_trampoline() that is implemented in the arch/x86_64/kernel/kprobes.c (More on this later) * When a return probe is registered using register_kretprobe(), kernel/kprobes.c will install a kprobe on the first instruction of the targeted function with the pre handler set to arch_prepare_kretprobe() which is implemented in arch/x86_64/kernel/kprobes.c. * arch_prepare_kretprobe() will prepare a kretprobe instance that stores: - nodes for hanging this instance in an empty or free list - a pointer to the return probe - the original return address - a pointer to the stack address With all this stowed away, arch_prepare_kretprobe() then sets the return address for the targeted function to a special trampoline function called kretprobe_trampoline() implemented in arch/x86_64/kernel/kprobes.c * The kprobe completes as normal, with control passing back to the target function that executes as normal, and eventually returns to our trampoline function. * Since a kprobe was installed on kretprobe_trampoline() during system initialization, control passes back to kprobes via the architecture specific function trampoline_probe_handler() which will lookup the instance in an hlist maintained by kernel/kprobes.c, and then call the handler function. * When trampoline_probe_handler() is done, the kprobes infrastructure single steps the original instruction (in this case just a top), and then calls trampoline_post_handler(). trampoline_post_handler() then looks up the instance again, puts the instance back on the free list, and then makes a long jump back to the original return instruction. So to recap, to instrument the exit path of a function this implementation will cause four interruptions: - A breakpoint at the very beginning of the function allowing us to switch out the return address - A single step interruption to execute the original instruction that we replaced with the break instruction (normal kprobe flow) - A breakpoint in the trampoline function where our instrumented function returned to - A single step interruption to execute the original instruction that we replaced with the break instruction (normal kprobe flow) Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86_64/kernel/kprobes.c98
-rw-r--r--arch/x86_64/kernel/process.c16
2 files changed, 113 insertions, 1 deletions
diff --git a/arch/x86_64/kernel/kprobes.c b/arch/x86_64/kernel/kprobes.c
index f77f8a0ff187..203672ca7401 100644
--- a/arch/x86_64/kernel/kprobes.c
+++ b/arch/x86_64/kernel/kprobes.c
@@ -27,6 +27,8 @@
* <prasanna@in.ibm.com> adapted for x86_64
* 2005-Mar Roland McGrath <roland@redhat.com>
* Fixed to handle %rip-relative addressing mode correctly.
+ * 2005-May Rusty Lynch <rusty.lynch@intel.com>
+ * Added function return probes functionality
*/
#include <linux/config.h>
@@ -240,6 +242,50 @@ static void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
regs->rip = (unsigned long)p->ainsn.insn;
}
+struct task_struct *arch_get_kprobe_task(void *ptr)
+{
+ return ((struct thread_info *) (((unsigned long) ptr) &
+ (~(THREAD_SIZE -1))))->task;
+}
+
+void arch_prepare_kretprobe(struct kretprobe *rp, struct pt_regs *regs)
+{
+ unsigned long *sara = (unsigned long *)regs->rsp;
+ struct kretprobe_instance *ri;
+ static void *orig_ret_addr;
+
+ /*
+ * Save the return address when the return probe hits
+ * the first time, and use it to populate the (krprobe
+ * instance)->ret_addr for subsequent return probes at
+ * the same addrress since stack address would have
+ * the kretprobe_trampoline by then.
+ */
+ if (((void*) *sara) != kretprobe_trampoline)
+ orig_ret_addr = (void*) *sara;
+
+ if ((ri = get_free_rp_inst(rp)) != NULL) {
+ ri->rp = rp;
+ ri->stack_addr = sara;
+ ri->ret_addr = orig_ret_addr;
+ add_rp_inst(ri);
+ /* Replace the return addr with trampoline addr */
+ *sara = (unsigned long) &kretprobe_trampoline;
+ } else {
+ rp->nmissed++;
+ }
+}
+
+void arch_kprobe_flush_task(struct task_struct *tk)
+{
+ struct kretprobe_instance *ri;
+ while ((ri = get_rp_inst_tsk(tk)) != NULL) {
+ *((unsigned long *)(ri->stack_addr)) =
+ (unsigned long) ri->ret_addr;
+ recycle_rp_inst(ri);
+ }
+}
+
/*
* Interrupts are disabled on entry as trap3 is an interrupt gate and they
* remain disabled thorough out this function.
@@ -317,6 +363,55 @@ no_kprobe:
}
/*
+ * For function-return probes, init_kprobes() establishes a probepoint
+ * here. When a retprobed function returns, this probe is hit and
+ * trampoline_probe_handler() runs, calling the kretprobe's handler.
+ */
+ void kretprobe_trampoline_holder(void)
+ {
+ asm volatile ( ".global kretprobe_trampoline\n"
+ "kretprobe_trampoline: \n"
+ "nop\n");
+ }
+
+/*
+ * Called when we hit the probe point at kretprobe_trampoline
+ */
+int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
+{
+ struct task_struct *tsk;
+ struct kretprobe_instance *ri;
+ struct hlist_head *head;
+ struct hlist_node *node;
+ unsigned long *sara = (unsigned long *)regs->rsp - 1;
+
+ tsk = arch_get_kprobe_task(sara);
+ head = kretprobe_inst_table_head(tsk);
+
+ hlist_for_each_entry(ri, node, head, hlist) {
+ if (ri->stack_addr == sara && ri->rp) {
+ if (ri->rp->handler)
+ ri->rp->handler(ri, regs);
+ }
+ }
+ return 0;
+}
+
+void trampoline_post_handler(struct kprobe *p, struct pt_regs *regs,
+ unsigned long flags)
+{
+ struct kretprobe_instance *ri;
+ /* RA already popped */
+ unsigned long *sara = ((unsigned long *)regs->rsp) - 1;
+
+ while ((ri = get_rp_inst(sara))) {
+ regs->rip = (unsigned long)ri->ret_addr;
+ recycle_rp_inst(ri);
+ }
+ regs->eflags &= ~TF_MASK;
+}
+
+/*
* Called after single-stepping. p->addr is the address of the
* instruction whose first byte has been replaced by the "int 3"
* instruction. To avoid the SMP problems that can occur when we
@@ -404,7 +499,8 @@ int post_kprobe_handler(struct pt_regs *regs)
if (current_kprobe->post_handler)
current_kprobe->post_handler(current_kprobe, regs, 0);
- resume_execution(current_kprobe, regs);
+ if (current_kprobe->post_handler != trampoline_post_handler)
+ resume_execution(current_kprobe, regs);
regs->eflags |= kprobe_saved_rflags;
unlock_kprobes();
diff --git a/arch/x86_64/kernel/process.c b/arch/x86_64/kernel/process.c
index dce8bab4306c..e59d1f9d6163 100644
--- a/arch/x86_64/kernel/process.c
+++ b/arch/x86_64/kernel/process.c
@@ -34,6 +34,7 @@
#include <linux/ptrace.h>
#include <linux/utsname.h>
#include <linux/random.h>
+#include <linux/kprobes.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
@@ -293,6 +294,14 @@ void exit_thread(void)
{
struct task_struct *me = current;
struct thread_struct *t = &me->thread;
+
+ /*
+ * Remove function-return probe instances associated with this task
+ * and put them back on the free list. Do not insert an exit probe for
+ * this function, it will be disabled by kprobe_flush_task if you do.
+ */
+ kprobe_flush_task(me);
+
if (me->thread.io_bitmap_ptr) {
struct tss_struct *tss = &per_cpu(init_tss, get_cpu());
@@ -312,6 +321,13 @@ void flush_thread(void)
struct task_struct *tsk = current;
struct thread_info *t = current_thread_info();
+ /*
+ * Remove function-return probe instances associated with this task
+ * and put them back on the free list. Do not insert an exit probe for
+ * this function, it will be disabled by kprobe_flush_task if you do.
+ */
+ kprobe_flush_task(tsk);
+
if (t->flags & _TIF_ABI_PENDING)
t->flags ^= (_TIF_ABI_PENDING | _TIF_IA32);