[RFC PATCH 02/14] x86/kprobes: Use generic kretprobe trampoline handler

Masami Hiramatsu
2020-08-26T13:46:48Z

arch/x86/kernel/kprobes/core.c | 109 +---------------------------------------
1 file changed, 4 insertions(+), 105 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 2ca10b770cff..45cfaa097110 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -767,123 +767,22 @@ asm(
NOKPROBE_SYMBOL(kretprobe_trampoline);
STACK_FRAME_NON_STANDARD(kretprobe_trampoline);

+
/*
* Called from kretprobe_trampoline
*/
__used __visible void *trampoline_handler(struct pt_regs *regs)
{
- struct kretprobe_instance *ri = NULL;
- struct hlist_head *head, empty_rp;
- struct hlist_node *tmp;
- unsigned long flags, orig_ret_address = 0;
- unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
- kprobe_opcode_t *correct_ret_addr = NULL;
- void *frame_pointer;
- bool skipped = false;
-
- /*
- * Set a dummy kprobe for avoiding kretprobe recursion.
- * Since kretprobe never run in kprobe handler, kprobe must not
- * be running at this point.
- */
- kprobe_busy_begin();
-
- INIT_HLIST_HEAD(&empty_rp);
- kretprobe_hash_lock(current, &head, &flags);
/* fixup registers */
regs->cs = __KERNEL_CS;
#ifdef CONFIG_X86_32
regs->gs = 0;
#endif
- /* We use pt_regs->sp for return address holder. */
- frame_pointer = &regs->sp;
- regs->ip = trampoline_address;
+ regs->ip = (unsigned long)&kretprobe_trampoline;
regs->orig_ax = ~0UL;

- /*
- * It is possible to have multiple instances associated with a given
- * task either because multiple functions in the call path have
- * return probes installed on them, and/or more than one
- * return probe was registered for a target function.
- *
- * We can handle this because:
- * - instances are always pushed into the head of the list
- * - when multiple return probes are registered for the same
- * function, the (chronologically) first instance's ret_addr
- * will be the real return address, and all the rest will
- * point to kretprobe_trampoline.
- */
- hlist_for_each_entry(ri, head, hlist) {
- if (ri->task != current)
- /* another task is sharing our hash bucket */
- continue;
- /*
- * Return probes must be pushed on this hash list correct
- * order (same as return order) so that it can be popped
- * correctly. However, if we find it is pushed it incorrect
- * order, this means we find a function which should not be
- * probed, because the wrong order entry is pushed on the
- * path of processing other kretprobe itself.
- */
- if (ri->fp != frame_pointer) {
- if (!skipped)
- pr_warn("kretprobe is stacked incorrectly. Trying to fixup.\n");
- skipped = true;
- continue;
- }
-
- orig_ret_address = (unsigned long)ri->ret_addr;
- if (skipped)
- pr_warn("%ps must be blacklisted because of incorrect kretprobe order\n",
- ri->rp->kp.addr);
-
- if (orig_ret_address != trampoline_address)
- /*
- * This is the real return address. Any other
- * instances associated with this task are for
- * other calls deeper on the call stack
- */
- break;
- }
-
- kretprobe_assert(ri, orig_ret_address, trampoline_address);
-
- correct_ret_addr = ri->ret_addr;
- hlist_for_each_entry_safe(ri, tmp, head, hlist) {
- if (ri->task != current)
- /* another task is sharing our hash bucket */
- continue;
- if (ri->fp != frame_pointer)
- continue;
-
- orig_ret_address = (unsigned long)ri->ret_addr;
- if (ri->rp && ri->rp->handler) {
- __this_cpu_write(current_kprobe, &ri->rp->kp);
- ri->ret_addr = correct_ret_addr;
- ri->rp->handler(ri, regs);
- __this_cpu_write(current_kprobe, &kprobe_busy);
- }
-
- recycle_rp_inst(ri, &empty_rp);
-
- if (orig_ret_address != trampoline_address)
- /*
- * This is the real return address. Any other
- * instances associated with this task are for
- * other calls deeper on the call stack
- */
- break;
- }
-
- kretprobe_hash_unlock(current, &flags);
-
- kprobe_busy_end();
-
- hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
- hlist_del(&ri->hlist);
- kfree(ri);
- }
- return (void *)orig_ret_address;
+ return (void *)kretprobe_trampoline_handler(regs,
+ (unsigned long)&kretprobe_trampoline, &regs->sp);
}
NOKPROBE_SYMBOL(trampoline_handler);