Re: [PATCH v4 02/17] x86/entry/64/compat: Fix bad fast syscall arg failure path

Ingo Molnar
2015-06-30T11:06:58Z

* Borislav Petkov <bp@alien8.de> wrote:

> On Mon, Jun 29, 2015 at 12:33:34PM -0700, Andy Lutomirski wrote:
> > diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
> > index bb187a6a877c..efe0b1e499fa 100644
> > --- a/arch/x86/entry/entry_64_compat.S
> > +++ b/arch/x86/entry/entry_64_compat.S
> > @@ -425,8 +425,39 @@ cstar_tracesys:
> > END(entry_SYSCALL_compat)
> >
> > ia32_badarg:
> > - ASM_CLAC
> > - movq $-EFAULT, RAX(%rsp)
> > + /*
> > + * So far, we've entered kernel mode, set AC, turned on IRQs, and
> > + * saved C regs except r8-r11. We haven't done any of the other
> > + * standard entry work, though. We want to bail, but we shouldn't
> > + * treat this as a syscall entry since we don't even know what the
> > + * args are. Instead, treat this as a non-syscall entry, finish
> > + * the entry work, and immediately exit after setting AX = -EFAULT.
> > + *
> > + * We're really just being polite here. Killing the task outright
> > + * would be a reasonable action, too. Given that the only valid
> > + * way to have gotten here is through the vDSO, and we already know
> > + * that the stack pointer is bad, the task isn't going to survive
> > + * for long no matter what we do.
>
> You mean something like
>
> force_sig_info(SIGSEGV, &si, current);
>
> ?

We should also emit a warning message, even if user-space installed a 'special'
sigfault handler to hide such failures. (I'm looking at you systemd!)

Thanks,

Ingo