On Thu, 8 Jun 2017 08:25:31 +0200
Heiko Carstens <heiko.carstens@xxxxxxxxxx> wrote:
> On Thu, Jun 08, 2017 at 07:35:28AM +0200, Martin Schwidefsky wrote:
> > On Wed, 7 Jun 2017 22:47:56 +0200
> > Heiko Carstens <heiko.carstens@xxxxxxxxxx> wrote:
> > > On Wed, Jun 07, 2017 at 02:34:40PM +0200, Martin Schwidefsky wrote:
> > > > +#define arch_elf_pt_proc(ehdr, phdr, elf, interp, state) \
> > > > +({ \
> > > > + struct elf64_hdr *_ehdr = (void *) ehdr; \
> > > > + struct elf64_phdr *_phdr = (void *) phdr; \
> > > > + int _rc = 0; \
> > > > + if (_ehdr->e_ident[EI_CLASS] == ELFCLASS64 && \
> > > > + _phdr->p_type == PT_S390_REQUEST_PGSTE && \
> > > > + !page_table_allocate_pgste && \
> > > > + !test_thread_flag(TIF_REQUEST_PGSTE)) { \
> > > > + set_thread_flag(TIF_REQUEST_PGSTE); \
> > > > + set_pt_regs_flag(task_pt_regs(current), \
> > > > + PIF_SYSCALL_RESTART); \
> > > > + _rc = -EAGAIN; \
> > > > + } \
> > > > + _rc; \
> > > > +})
> > >
> > > I'm wondering if this should simply fail, if a PT_S390_REQUEST_PGSTE type
> > > segment exists, but it is not ELFCLASS64?
> > > It will fail later anyway on s390_enable_sie(), but...
> >
> > Does it matter if it fails for a 32-bit ELF file? Just makes the code more
> > complex without benefit, no?
>
> It would be more consistent, since right now a 32-bit ELF file with
> PT_S390_REQUEST_PGSTE will be exectuted, but the page tables won't have any
> pgstes. That's sort of odd, isn't it? And that later on it won't be able to
> create a virtual machine because our current implementation doesn't allow
> that for compat tasks is sort of unrelated.
> But anyway, I'll leave that up to you, it doesn't really matter.
Actually the code will be less complex if we add PT_S390_REQUEST_PGSTE for
32-bit ELF files as well. It does not make sense to define the segment for
a compat process as KVM won't work but you get what you ask for..
This looks like this:
#define arch_elf_pt_proc(ehdr, phdr, elf, interp, state) \
({ \
int _rc = 0; \
if (phdr->p_type == PT_S390_REQUEST_PGSTE && \
!page_table_allocate_pgste && \
!test_thread_flag(TIF_REQUEST_PGSTE)) { \
set_thread_flag(TIF_REQUEST_PGSTE); \
set_pt_regs_flag(task_pt_regs(current), \
PIF_SYSCALL_RESTART); \
_rc = -EAGAIN; \
} \
_rc; \
})
phdr is a (struct elf_phd *) which is either define to a a (struct elf64_phdr *)
or a (struct elf32_phdr *). The check works in both cases.
> >
> > > > diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
> > > > index c119d564d8f2..1201b18e817d 100644
> > > > --- a/arch/s390/include/asm/mmu_context.h
> > > > +++ b/arch/s390/include/asm/mmu_context.h
> > > > @@ -25,7 +25,8 @@ static inline int init_new_context(struct task_struct *tsk,
> > > > mm->context.gmap_asce = 0;
> > > > mm->context.flush_mm = 0;
> > > > #ifdef CONFIG_PGSTE
> > > > - mm->context.alloc_pgste = page_table_allocate_pgste;
> > > > + mm->context.alloc_pgste = page_table_allocate_pgste ||
> > > > + test_thread_flag(TIF_REQUEST_PGSTE);
> > >
> > > I think the alloc_pgste flag should be inherited on fork, no?
> >
> > Yes, that makes it more consistent. I'll add it.
>
> By the way, what prevents with the _current_ code a scenario like:
>
> - set allocate_pgste sysctl to 1
> - create kvm guest
> - s390_enable_sie
> - run vcpu
> - set allocate_pgste sysctl to 0
> - clone(... CLONE_FILES ...) (that is: new mm without pgstes, but shared fds)
> - [child] run vcpu
>
> Is there anything that makes sure we cannot execute the sie instruction in
> the child process?
Yes, that looks like a loop-hole.
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
