Re: [PATCH v5 08/14] KVM: s390: pv: handle secure storage exceptions for normal guests

Claudio Imbrenda
2021-10-12T08:36:06Z

On Tue, 12 Oct 2021 10:16:26 +0200
Janosch Frank <frankja@linux.ibm.com> wrote:

> On 9/20/21 15:24, Claudio Imbrenda wrote:
> > With upcoming patches, normal guests might touch secure pages.
> >
> > This patch extends the existing exception handler to convert the pages
> > to non secure also when the exception is triggered by a normal guest.
> >
> > This can happen for example when a secure guest reboots; the first
> > stage of a secure guest is non secure, and in general a secure guest
> > can reboot into non-secure mode.
> >
> > If the secure memory of the previous boot has not been cleared up
> > completely yet, a non-secure guest might touch secure memory, which
> > will need to be handled properly.
> >
> > Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> > ---
> > arch/s390/mm/fault.c | 10 +++++++++-
> > 1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> > index eb68b4f36927..74784581f42d 100644
> > --- a/arch/s390/mm/fault.c
> > +++ b/arch/s390/mm/fault.c
> > @@ -767,6 +767,7 @@ void do_secure_storage_access(struct pt_regs *regs)
> > struct vm_area_struct *vma;
> > struct mm_struct *mm;
> > struct page *page;
> > + struct gmap *gmap;
> > int rc;
> >
> > /*
> > @@ -796,6 +797,14 @@ void do_secure_storage_access(struct pt_regs *regs)
> > }
> >
> > switch (get_fault_type(regs)) {
> > + case GMAP_FAULT:
> > + gmap = (struct gmap *)S390_lowcore.gmap;
> > + addr = __gmap_translate(gmap, addr);
> > + if (IS_ERR_VALUE(addr)) {
> > + do_fault_error(regs, VM_ACCESS_FLAGS, VM_FAULT_BADMAP);
> > + break;
> > + }
> > + fallthrough;
>
> This would trigger an export and not a destroy, right?

correct. but this would only happen for leftover secure pages touched
by non-secure guests, before the background thread could clean them up.

>
> > case USER_FAULT:
> > mm = current->mm;
> > mmap_read_lock(mm);
> > @@ -824,7 +833,6 @@ void do_secure_storage_access(struct pt_regs *regs)
> > if (rc)
> > BUG();
> > break;
> > - case GMAP_FAULT:
> > default:
> > do_fault_error(regs, VM_READ | VM_WRITE, VM_FAULT_BADMAP);
> > WARN_ON_ONCE(1);
> >
>