CVE-2024-40915

In the Linux kernel, the following vulnerability has been resolved: riscv: rewrite __kernel_map_pages() to fix sleeping in invalid context __kernel_map_pages() is a debug function which clears the valid bit in page table entry for deallocated pages to detect illegal memory accesses to freed pages. This function set/clear the valid bit using __set_memory(). __set_memory() acquires init_mm's semaphore, and this operation may sleep. This is problematic, because __kernel_map_pages() can be called in atomic context, and thus is illegal to sleep. An example warning that this causes: BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:1578 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 2, name: kthreadd preempt_count: 2, expected: 0 CPU: 0 PID: 2 Comm: kthreadd Not tainted 6.9.0-g1d4c6d784ef6 #37 Hardware name: riscv-virtio,qemu (DT) Call Trace: [ ] dump_backtrace+0x1c/0x24 [ ] show_stack+0x2c/0x38 [ ] dump_stack_lvl+0x5a/0x72 [ ] dump_stack+0x14/0x1c [ ] __might_resched+0x104/0x10e [ ] __might_sleep+0x3e/0x62 [ ] down_write+0x20/0x72 [ ] __set_memory+0x82/0x2fa [ ] __kernel_map_pages+0x5a/0xd4 [ ] __alloc_pages_bulk+0x3b2/0x43a [ ] __vmalloc_node_range+0x196/0x6ba [ ] copy_process+0x72c/0x17ec [ ] kernel_clone+0x60/0x2fe [ ] kernel_thread+0x82/0xa0 [ ] kthreadd+0x14a/0x1be [ ] ret_from_fork+0xe/0x1c Rewrite this function with apply_to_existing_page_range(). It is fine to not have any locking, because __kernel_map_pages() works with pages being allocated/deallocated and those pages are not changed by anyone else in the meantime.