On Mon, Jul 18, 2022 at 02:48:21PM +0100, Matthew Wilcox wrote:
> On Mon, Jul 18, 2022 at 03:32:40PM +0200, Alexander Gordeev wrote:
> > +++ b/arch/s390/kernel/crash_dump.c
> > @@ -53,6 +53,7 @@ struct save_area {
> > };
> >
> > static LIST_HEAD(dump_save_areas);
>
> I'd suggest you need a mutex here so that simultaneous calls to
> copy_to_user_real() don't corrupt each others data.
We stop all (but one) CPUs before calling into the capture kernel -
one that calls these functions. Similarily to racy hsa_buf[] access
from memcpy_hsa_iter() this should not hit.
As you noticed last time, it is a pre-existing race and I was
actually going to address it in a separate fix - if the problem
really exists.
> > +static char memcpy_real_buf[PAGE_SIZE];
> >
> > /*
> > * Allocate a save area
> > @@ -179,23 +180,18 @@ int copy_oldmem_kernel(void *dst, unsigned long src, size_t count)
> > static int copy_to_user_real(void __user *dest, unsigned long src, unsigned long count)
> > {
> > int offs = 0, size, rc;
> > - char *buf;
> >
> > - buf = (char *)__get_free_page(GFP_KERNEL);
> > - if (!buf)
> > - return -ENOMEM;
> > rc = -EFAULT;
> > while (offs < count) {
> > size = min(PAGE_SIZE, count - offs);
> > - if (memcpy_real(buf, src + offs, size))
> > + if (memcpy_real(memcpy_real_buf, src + offs, size))
> > goto out;
> > - if (copy_to_user(dest + offs, buf, size))
> > + if (copy_to_user(dest + offs, memcpy_real_buf, size))
> > goto out;
> > offs += size;
> > }
> > rc = 0;
> > out:
> > - free_page((unsigned long)buf);
> > return rc;
> > }
Thanks!
