CVE-2021-46927

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] [ 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. Thats a similar pattern as mmap_read_lock() used together with get_user_pages().

Weakness

The product does not properly acquire or release a lock on a resource, leading to unexpected resource state changes and behaviors.

Affected Software

Extended Description

Locking is a type of synchronization behavior that ensures that multiple independently-operating processes or threads do not interfere with each other when accessing the same resource. All processes/threads are expected to follow the same steps for locking. If these steps are not followed precisely - or if no locking is done at all - then another process/thread could modify the shared resource in a way that is not visible or predictable to the original process. This can lead to data or memory corruption, denial of service, etc.

Potential Mitigations

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/25.html
• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/27.html

References

• https://git.kernel.org/stable/c/3a0152b219523227c2a62a0a122cf99608287176
• https://git.kernel.org/stable/c/90d2beed5e753805c5eab656b8d48257638fe543