lkml.org 
[lkml]   [2012]   [Dec]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [RFC PATCH 1/6] uretprobes/x86: hijack return address
On 12/21, Anton Arapov wrote:
>
> +extern unsigned long
> +arch_uretprobe_hijack_return_addr(unsigned long rp_trampoline_vaddr, struct pt_regs *regs)
> +{
> + struct uprobe_task *utask = current->utask;
> + int rasize, ncopied;
> + unsigned long orig_return_vaddr = 0; /* clear high bits for 32-bit apps */
> +
> + if (is_ia32_task())
> + rasize = 4;
> + else
> + rasize = 8;
> +
> + ncopied = copy_from_user(&orig_return_vaddr, (void __user *)regs->sp, rasize);
> + if (unlikely(ncopied))
> + return -EFAULT;

Hmm. The caller (added by 3/6) does

ri->orig_return_vaddr = arch_uretprobe_hijack_return_addr(...);
if (likely(ri->orig_return_vaddr)) {


> + ncopied = copy_to_user((void __user *)regs->sp, &rp_trampoline_vaddr, rasize);
> + if (unlikely(ncopied)) {
> + if (ncopied != rasize) {
> + printk(KERN_ERR "uretprobe: return address clobbered: "
> + "pid=%d, %%sp=%#lx, %%ip=%#lx\n",
> + current->pid, regs->sp, regs->ip);

OK... perhaps we could try to write rasize - ncopied bytes first, but
this is minor.

> + utask->doomed = true;

But this looks strange. We set ->doomed = true, but the task continues to run.
I think in this case we should send SIGTRAP right now. We should not wait until
handle_swbp() notices this flag (which btw can never happen). And this also
means ->doomed should die.

> + return -EFAULT;

Again, NULL or fix the caller.

> + * On x86_32, if a function returns a struct or union, the return
> + * value is copied into an area created by the caller. The address
> + * of this area is passed on the stack as a "hidden" first argument.
> + * When such a function returns, it uses a "ret $4" instruction to pop
> + * not only the return address but also the hidden arg. To accommodate
> + * such functions, we add 4 bytes of slop when predicting the return
> + * address. See PR #10078.
^^^^^^^^^
I'd wish I knew what this "PR" means ;)


> +#define STRUCT_RETURN_SLOP 4
> +
> +extern unsigned long
> +arch_uretprobe_predict_sp_at_return(struct pt_regs *regs, struct task_struct *tsk)
> +{
> + if (test_tsk_thread_flag(tsk, TIF_IA32))
> + return (unsigned long) (regs->sp + 4 + STRUCT_RETURN_SLOP);

Somehow I can't understand the logic behind arch_uretprobe_predict_sp_at_return()
at all... I'll try more. but tsk is always current, I see no point to pass the
argument.

> @@ -60,6 +63,12 @@ struct uprobe_task {
>
> unsigned long xol_vaddr;
> unsigned long vaddr;
> +
> + /*
> + * Unexpected error in probe point handling has left task's
> + * text or stack corrupted. Kill task ASAP.
^^^^^^^^^^^^^^
Exactly, so ...

> + bool doomed;

must die, I think.

Oleg.


\
 
 \ /
  Last update: 2012-12-22 17:41    [W:0.101 / U:2.420 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site