* Eric Biggers <ebigge...@gmail.com> wrote:
> 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;
> }
Note that I think the whole series is more robust if it goes to -stable as-is,
as
the ABI aspect should not be underestimated either. Nevertheless I've
backmerged
the fix further to the original commit, to maintain bisectability.
> Also can you please fix the commit title and message of this patch? It should
> say "__fpu__restore_sig()", not "sanitize_restored_xstate()".
Indeed - and I fixed that too. I have pushed out the latest tip:WIP.x86/fpu -
no
change in the end result tree, but different inner structure.
Thanks,
Ingo
