On Mon, Sep 25, 2017 at 08:14:45AM +0200, Ingo Molnar wrote:
> > >
> > > Could you please just send the delta patch against the whole tree to fix
> > > the bug?
> > > I'll worry about the patch dependencies and back-merge it to the proper
> > > place.
> > >
> >
> > The following diff against tip/master fixes the bug. Note: we *could* check
> > 'use_xsave()' instead of 'state_size > offsetof(struct xregs_state,
> > header)',
> > but that might be confusing in the case where we couldn't find the xstate
> > information in the memory layout and only copy the fxregs_state, since then
> > we'd
> > actually be validating the xsave_header which was already there, which
> > shouldn't
> > ever fail.
> >
> > diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
> > index afe54247cf27..fb639e70048f 100644
> > --- a/arch/x86/kernel/fpu/signal.c
> > +++ b/arch/x86/kernel/fpu/signal.c
> > @@ -331,7 +331,8 @@ static int __fpu__restore_sig(void __user *buf, void
> > __user *buf_fx, int size)
> > err = copy_user_to_xstate(&fpu->state.xsave, buf_fx);
> > } else {
> > err = __copy_from_user(&fpu->state.xsave, buf_fx,
> > state_size);
> > - if (!err)
> > +
> > + if (!err && state_size > offsetof(struct xregs_state,
> > header))
> > err =
> > validate_xstate_header(&fpu->state.xsave.header);
> > }
>
> I.e. a better check would be to check that the whole header can be accessed:
>
> state_size >= offsetof(struct xregs_state, header) + sizeof(struct
> xstate_header)
>
> Not that there should ever be a 'state_size' that points inside the header -
> so in
> the end I back-merged your original (and tested ...) version.
>
Well, actually we'd need to validate the header if userspace overwrote any part
of it.
But more importantly, I think the state_size check needs to go into the first
patch (the one that's Cc'ed to stable as it fixes the real bug), since
->xcomp_bv is part of the xstate_header. So *before* we switch to
validate_xstate_header() in this patch, the code should already be:
if (using_compacted_format()) {
err = copy_user_to_xstate(&fpu->state.xsave, buf_fx);
} else {
err = __copy_from_user(&fpu->state.xsave, buf_fx,
state_size);
/* xcomp_bv must be 0 when using uncompacted format */
if (!err &&
state_size > offsetof(struct xregs_state, header) &&
fpu->state.xsave.header.xcomp_bv)
err = -EINVAL;
}
Also can you please fix the commit title and message of this patch? It should
say "__fpu__restore_sig()", not "sanitize_restored_xstate()".
Thanks,
Eric
