* Eric Biggers <ebigge...@gmail.com> wrote:
> On Sun, Sep 24, 2017 at 09:02:42PM +0200, Ingo Molnar wrote:
> >
> > * Eric Biggers <ebigge...@gmail.com> wrote:
> >
> > > On Sun, Sep 24, 2017 at 12:59:06PM +0200, Ingo Molnar wrote:
> > > > @@ -328,10 +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);
> > > > -
> > > > - /* xcomp_bv must be 0 when using uncompacted
> > > > format */
> > > > - if (!err && fpu->state.xsave.header.xcomp_bv)
> > > > - err = -EINVAL;
> > > > + if (!err)
> > > > + err =
> > > > validate_xstate_header(&fpu->state.xsave.header);
> > > > }
> > > >
> > >
> > > Sorry, this is the buggy part. The problem is that this code runs even
> > > if XSAVE
> > > isn't being used --- and in that case the state size is 512 bytes or
> > > less, so
> > > the state doesn't actually include the xstate_header. So
> > > validate_xstate_header() was reading out of bounds and seeing invalid
> > > values.
> > >
> > > So I think we need to check use_xsave() here, but it really needs to be
> > > in the
> > > earlier patch which added the check for just ->xcomp_bv ("x86/fpu: Don't
> > > let
> > > userspace set bogus xcomp_bv"), not in this one.
> > >
> > > As far the split of patch 2/3 into these 10 patches, it looks fine
> > > (though it
> > > suddenly became a *lot* of patches!). One nit: the subject of this one
> > > really
> > > should say "__fpu__restore_sig()", not "sanitize_restored_xstate()".
> > >
> > > I can send a fixed series when I have a chance.
> >
> > 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.
Thanks,
Ingo
