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uretprobes: Return probe entry, prepare_uretprobe() 

When a uprobe with return probe consumer is hit, prepare_uretprobe()
function is invoked. It creates return_instance, hijacks return address
and replaces it with the trampoline.

* Return instances are kept as stack per uprobed task.
* Return instance is chained, when the original return address is
  trampoline's page vaddr (e.g. recursive call of the probed function).

Signed-off-by: Anton Arapov <anton@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
This commit is contained in:
Anton Arapov 2013-04-03 18:00:35 +02:00 committed by Oleg Nesterov
parent f15706b79d
commit 0dfd0eb8e4
2 changed files with 92 additions and 1 deletions
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1
include/linux/uprobes.h
View File

@ -71,6 +71,7 @@ struct uprobe_task {
enum uprobe_task_state state;
struct arch_uprobe_task autask;
struct return_instance *return_instances;
struct uprobe *active_uprobe;
unsigned long xol_vaddr;

92
kernel/events/uprobes.c
View File

@ -75,6 +75,15 @@ struct uprobe {
struct arch_uprobe arch;
};
struct return_instance {
struct uprobe *uprobe;
unsigned long func;
unsigned long orig_ret_vaddr; /* original return address */
bool chained; /* true, if instance is nested */
struct return_instance *next; /* keep as stack */
};
/*
* valid_vma: Verify if the specified vma is an executable vma
* Relax restrictions while unregistering: vm_flags might have
@ -1317,6 +1326,7 @@ unsigned long __weak uprobe_get_swbp_addr(struct pt_regs *regs)
void uprobe_free_utask(struct task_struct *t)
{
struct uprobe_task *utask = t->utask;
struct return_instance *ri, *tmp;
if (!utask)
return;
@ -1324,6 +1334,15 @@ void uprobe_free_utask(struct task_struct *t)
if (utask->active_uprobe)
put_uprobe(utask->active_uprobe);
ri = utask->return_instances;
while (ri) {
tmp = ri;
ri = ri->next;
put_uprobe(tmp->uprobe);
kfree(tmp);
}
xol_free_insn_slot(t);
kfree(utask);
t->utask = NULL;
@ -1371,6 +1390,65 @@ static unsigned long get_trampoline_vaddr(void)
return trampoline_vaddr;
}
static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
{
struct return_instance *ri;
struct uprobe_task *utask;
unsigned long orig_ret_vaddr, trampoline_vaddr;
bool chained = false;
if (!get_xol_area())
return;
utask = get_utask();
if (!utask)
return;
ri = kzalloc(sizeof(struct return_instance), GFP_KERNEL);
if (!ri)
goto fail;
trampoline_vaddr = get_trampoline_vaddr();
orig_ret_vaddr = arch_uretprobe_hijack_return_addr(trampoline_vaddr, regs);
if (orig_ret_vaddr == -1)
goto fail;
/*
* We don't want to keep trampoline address in stack, rather keep the
* original return address of first caller thru all the consequent
* instances. This also makes breakpoint unwrapping easier.
*/
if (orig_ret_vaddr == trampoline_vaddr) {
if (!utask->return_instances) {
/*
* This situation is not possible. Likely we have an
* attack from user-space.
*/
pr_warn("uprobe: unable to set uretprobe pid/tgid=%d/%d\n",
current->pid, current->tgid);
goto fail;
}
chained = true;
orig_ret_vaddr = utask->return_instances->orig_ret_vaddr;
}
atomic_inc(&uprobe->ref);
ri->uprobe = uprobe;
ri->func = instruction_pointer(regs);
ri->orig_ret_vaddr = orig_ret_vaddr;
ri->chained = chained;
/* add instance to the stack */
ri->next = utask->return_instances;
utask->return_instances = ri;
return;
fail:
kfree(ri);
}
/* Prepare to single-step probed instruction out of line. */
static int
pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
@ -1527,6 +1605,7 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
{
struct uprobe_consumer *uc;
int remove = UPROBE_HANDLER_REMOVE;
bool need_prep = false; /* prepare return uprobe, when needed */
down_read(&uprobe->register_rwsem);
for (uc = uprobe->consumers; uc; uc = uc->next) {
@ -1537,9 +1616,16 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
WARN(rc & ~UPROBE_HANDLER_MASK,
"bad rc=0x%x from %pf()\n", rc, uc->handler);
}
if (uc->ret_handler)
need_prep = true;
remove &= rc;
}
if (need_prep && !remove)
prepare_uretprobe(uprobe, regs); /* put bp at return */
if (remove && uprobe->consumers) {
WARN_ON(!uprobe_is_active(uprobe));
unapply_uprobe(uprobe, current->mm);
@ -1658,7 +1744,11 @@ void uprobe_notify_resume(struct pt_regs *regs)
*/
int uprobe_pre_sstep_notifier(struct pt_regs *regs)
{
if (!current->mm || !test_bit(MMF_HAS_UPROBES, &current->mm->flags))
if (!current->mm)
return 0;
if (!test_bit(MMF_HAS_UPROBES, &current->mm->flags) &&
(!current->utask || !current->utask->return_instances))
return 0;
set_thread_flag(TIF_UPROBE);