From: Christopher M. Riedl
> Sent: 01 February 2021 15:56
>
> On Thu Jan 28, 2021 at 4:38 AM CST, David Laight wrote:
> > From: Christopher M. Riedl
> > > Sent: 28 January 2021 04:04
> > >
> > > Reuse the "safe" implementation from signal.c except for calling
> > > unsafe_copy_from_user() to copy into a local buffer.
> > >
> > > Signed-off-by: Christopher M. Riedl <c...@codefail.de>
> > > ---
> > > arch/powerpc/kernel/signal.h | 33 +++++++++++++++++++++++++++++++++
> > > 1 file changed, 33 insertions(+)
> > >
> > > diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
> > > index 2559a681536e..c18402d625f1 100644
> > > --- a/arch/powerpc/kernel/signal.h
> > > +++ b/arch/powerpc/kernel/signal.h
> > > @@ -53,6 +53,33 @@ unsigned long copy_ckfpr_from_user(struct task_struct
> > > *task, void __user *from);
> > > &buf[i], label);\
> > > } while (0)
> > >
> > > +#define unsafe_copy_fpr_from_user(task, from, label) do {
> > > \
> > > + struct task_struct *__t = task; \
> > > + u64 __user *__f = (u64 __user *)from; \
> > > + u64 buf[ELF_NFPREG]; \
> >
> > How big is that buffer?
> > Isn't is likely to be reasonably large compared to a reasonable
> > kernel stack frame.
> > Especially since this isn't even a leaf function.
> >
>
> I think Christophe answered this - I don't really have an opinion either
> way. What would be a 'reasonable' kernel stack frame for reference?
Zero :-)
>
> > > + int i; \
> > > + \
> > > + unsafe_copy_from_user(buf, __f, ELF_NFPREG * sizeof(double), \
> > > + label); \
> > > + for (i = 0; i < ELF_NFPREG - 1; i++) \
> > > + __t->thread.TS_FPR(i) = buf[i]; \
> > > + __t->thread.fp_state.fpscr = buf[i]; \
> > > +} while (0)
On further reflection, since you immediately loop through the buffer
why not just use user_access_begin() and unsafe_get_user() in the loop.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT,
UK
Registration No: 1397386 (Wales)
