nitro_enclaves: Use get_user_pages_unlocked() call to handle mmap assert

In the Linux kernel, the following vulnerability has been resolved:

nitro_enclaves: Use get_user_pages_unlocked() call to handle mmap assert

After commit 5b78ed24e8ec ("mm/pagemap: add mmap_assert_locked()

annotations to find_vma*()"), the call to get_user_pages() will trigger

the mmap assert.

static inline void mmap_assert_locked(struct mm_struct *mm)

{

lockdep_assert_held(&mm->mmap_lock);

VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);

}

[ 62.521410] kernel BUG at include/linux/mmap_lock.h:156!

...........................................................

[ 62.538938] RIP: 0010:find_vma+0x32/0x80

...........................................................

[ 62.605889] Call Trace:

[ 62.608502] <TASK>

[ 62.610956] ? lock_timer_base+0x61/0x80

[ 62.614106] find_extend_vma+0x19/0x80

[ 62.617195] __get_user_pages+0x9b/0x6a0

[ 62.620356] __gup_longterm_locked+0x42d/0x450

[ 62.623721] ? finish_wait+0x41/0x80

[ 62.626748] ? __kmalloc+0x178/0x2f0

[ 62.629768] ne_set_user_memory_region_ioctl.isra.0+0x225/0x6a0 [nitro_enclaves]

[ 62.635776] ne_enclave_ioctl+0x1cf/0x6d7 [nitro_enclaves]

[ 62.639541] __x64_sys_ioctl+0x82/0xb0

[ 62.642620] do_syscall_64+0x3b/0x90

[ 62.645642] entry_SYSCALL_64_after_hwframe+0x44/0xae

Use get_user_pages_unlocked() when setting the enclave memory regions.

That's a similar pattern as mmap_read_lock() used together with

get_user_pages().