Re: [PATCH 1/2] mmap locking API: Order lock of nascent mm outside lock of live mm

Jann Horn
2020-10-05T01:31:18Z

On Sat, Oct 3, 2020 at 11:30 PM Michel Lespinasse <walken@google.com> wrote:
> Unrelated to the above: copy_from_user and copy_to_user should not be
> called with mmap_lock held; it may be worth adding these assertions
> too (probably in separate patches) ?

We already have that: All (hopefully?) the userspace accessors call
might_fault(), and that does might_lock_read(&current->mm->mmap_lock)
(if we're not running in a lazytlb kernel thread or KERNEL_DS is on or
we're in IRQ context or page faults have explicitly been disabled).

But another place where lockdep asserts should be added is find_vma();
there are currently several architectures that sometimes improperly
call that with no lock held:

SPARC's arch_validate_prot():
https://lore.kernel.org/linux-mm/CAG48ez3YsfTfOFKa-Po58e4PNp7FK54MFbkK3aUPSRt3LWtxQA@mail.gmail.com/

nios2 sys_cacheflush():
https://lore.kernel.org/linux-mm/CAG48ez3hxeXU29UGWRH-gRXX2jb5Lc==npbXFt8UDrWO4eHZdQ@mail.gmail.com/

nds32 sys_cacheflush():