🇰🇷 한글 설명
Linux 커널의 x86 아키텍처에서 alternatives 패칭 코드 중 text poking 과정에서 발생하는 버그입니다. CONFIG_ARCH_HAS_EXECMEM_ROX 설정이 활성화된 환경에서 여러 모듈이 병렬로 메모리 속성을 변경할 때 vmalloc_to_page() 함수가 실패하여 커널 패닉(BUG)을 유발할 수 있습니다.
💡 쉬운 설명
컴퓨터의 핵심 운영체제인 리눅스 커널이 메모리를 수정하는 과정에서 충돌이 발생하여 시스템이 갑자기 멈추거나 오류를 일으키는 문제입니다. 특정 설정이 켜져 있을 때 여러 작업이 동시에 메모리를 건드리면 발생할 수 있습니다.
🇺🇸 원문 (English)
In the Linux kernel, the following vulnerability has been resolved:
x86/alternatives: Exclude text poking against change_page_attr()
From time to time, the following BUG can be observed
in the x86 alternatives patching code [0]:
> kernel BUG at arch/x86/kernel/alternative.c:2576!
> Oops: invalid opcode: 0000 [#1] SMP NOPTI
> CPU: 0 UID: 0 PID: 355 Comm: (udev-worker) Not tainted 7.1.3-1-default #1 PREEMPT(full) openSUSE Tumbleweed 8c1795b03ec64f997e57a8ad38b1161e3b98da64
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS unknown 02/02/2022
> RIP: 0010:__text_poke+0x2aa/0x450
> Call Trace:
> <TASK>
> smp_text_poke_batch_finish+0x2a7/0x320
> __static_call_transform+0xb7/0x220
> arch_static_call_transform+0x5b/0xb0
> __static_call_init+0xe9/0x270
> static_call_module_notify+0x11f/0x150
> notifier_call_chain+0x61/0xe0
> blocking_notifier_call_chain_robust+0x63/0xc0
> load_module+0x1c92/0x20c0
> init_module_from_file+0xd8/0x140
> idempotent_init_module+0x100/0x2f0
> __x64_sys_finit_module+0x71/0xe0
> do_syscall_64+0xe1/0x610
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
which matches the following BUG_ON() in alternative.c:
/*
* If something went wrong, crash and burn since recovery paths are not
* implemented.
*/
BUG_ON(!pages[0] || (cross_page_boundary && !pages[1]));
This can happen if vmalloc_to_page() fails, for any reason. Such can happen
if text poking races with CPA, which can possibly result in the collapsing
of page tables (or breaking of PMD hugepages). It is not a problem for most
users of vmalloc_to_page() (they solely own the vmalloc'd range) but, when
CONFIG_ARCH_HAS_EXECMEM_ROX=y, various modules own a single execmem vmalloc
range, and can call set_memory_*() in parallel on it. This can happen to
race against __text_poke and cause havoc in vmalloc_to_page().
Fix it by excluding against CPA using the init_mm mmap read lock.
[ dhansen: Fix up SoB ordering. The actual code flow here was:
Pedro=>Lorenzo=>Mike=>Me which is reflected in the SoB chain
now. I *believe* Mike simply picked up Lorenzo's update to
Pedro's post from the Link ]
📍 영향받는 시스템
Linux kernel (x86 architecture) with CONFIG_ARCH_HAS_EXECMEM_ROX=y enabled
⚔️ 공격 벡터
Local (Race condition during module loading or memory attribute changes)
🛡️ 대응 방법
Linux 커널을 최신 패치가 적용된 버전으로 업데이트하여 init_mm mmap read lock을 통한 CPA 보호를 적용해야 합니다.
🔧 검증 코드
출력된 커널 버전이 해당 취약점이 해결된 패치 버전 이후인지 확인합니다.