On Fri, Mar 01, 2013 at 11:15:36AM +0530, Ananth N Mavinakayanahalli wrote:
> On Thu, Feb 28, 2013 at 12:00:11PM +0100, Anton Arapov wrote:
> > hijack the return address and replace it with a "trampoline"
> >
> > v2:
> > - remove ->doomed flag, kill task immediately
> >
> > Signed-off-by: Anton Arapov <an...@redhat.com>
> > ---
> > arch/x86/include/asm/uprobes.h | 1 +
> > arch/x86/kernel/uprobes.c | 29 +++++++++++++++++++++++++++++
> > 2 files changed, 30 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
> > index 8ff8be7..c353555 100644
> > --- a/arch/x86/include/asm/uprobes.h
> > +++ b/arch/x86/include/asm/uprobes.h
> > @@ -55,4 +55,5 @@ extern int arch_uprobe_post_xol(struct arch_uprobe *aup,
> > struct pt_regs *regs);
> > extern bool arch_uprobe_xol_was_trapped(struct task_struct *tsk);
> > extern int arch_uprobe_exception_notify(struct notifier_block *self,
> > unsigned long val, void *data);
> > extern void arch_uprobe_abort_xol(struct arch_uprobe *aup, struct pt_regs
> > *regs);
> > +extern unsigned long arch_uretprobe_hijack_return_addr(unsigned long
> > rp_trampoline_vaddr, struct pt_regs *regs);
> > #endif /* _ASM_UPROBES_H */
> > diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> > index 0ba4cfb..85e2153 100644
> > --- a/arch/x86/kernel/uprobes.c
> > +++ b/arch/x86/kernel/uprobes.c
> > @@ -697,3 +697,32 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe
> > *auprobe, struct pt_regs *regs)
> > send_sig(SIGTRAP, current, 0);
> > return ret;
> > }
> > +
> > +extern unsigned long arch_uretprobe_hijack_return_addr(unsigned long
> > + rp_trampoline_vaddr, struct pt_regs *regs)
> > +{
> > + int rasize, ncopied;
> > + unsigned long orig_ret_vaddr = 0; /* clear high bits for 32-bit apps */
> > +
> > + rasize = is_ia32_task() ? 4 : 8;
> > + ncopied = copy_from_user(&orig_ret_vaddr, (void __user *)regs->sp,
> > rasize);
> > + if (unlikely(ncopied))
>
> What if ncopied < rasize? Agreed that the upper order bits can be 0, but
> should
> you not validate ncopied == rasize?
Function returns 0 in case copy_from_user() was not able to copy
return address entirely, and "if (ncopied)" makes sure of it. We
can't continue if we have no correct return address.
copy_from_user() returns number of bytes that were *not* copied,
thus "ncopied == rasize" means copy_from_user() was not able to copy
*all* bytes. I don't see the point of such check here.
Or am I missing anything?
thank you!
Anton.
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