From: He Ying heying24@huawei.com
[ Upstream commit a1b29ba2f2c171b9bea73be993bfdf0a62d37d15 ]
The following KASAN warning was reported in our kernel.
BUG: KASAN: stack-out-of-bounds in get_wchan+0x188/0x250 Read of size 4 at addr d216f958 by task ps/14437
CPU: 3 PID: 14437 Comm: ps Tainted: G O 5.10.0 #1 Call Trace: [daa63858] [c0654348] dump_stack+0x9c/0xe4 (unreliable) [daa63888] [c035cf0c] print_address_description.constprop.3+0x8c/0x570 [daa63908] [c035d6bc] kasan_report+0x1ac/0x218 [daa63948] [c00496e8] get_wchan+0x188/0x250 [daa63978] [c0461ec8] do_task_stat+0xce8/0xe60 [daa63b98] [c0455ac8] proc_single_show+0x98/0x170 [daa63bc8] [c03cab8c] seq_read_iter+0x1ec/0x900 [daa63c38] [c03cb47c] seq_read+0x1dc/0x290 [daa63d68] [c037fc94] vfs_read+0x164/0x510 [daa63ea8] [c03808e4] ksys_read+0x144/0x1d0 [daa63f38] [c005b1dc] ret_from_syscall+0x0/0x38 --- interrupt: c00 at 0x8fa8f4 LR = 0x8fa8cc
The buggy address belongs to the page: page:98ebcdd2 refcount:0 mapcount:0 mapping:00000000 index:0x2 pfn:0x1216f flags: 0x0() raw: 00000000 00000000 01010122 00000000 00000002 00000000 ffffffff 00000000 raw: 00000000 page dumped because: kasan: bad access detected
Memory state around the buggy address: d216f800: 00 00 00 00 00 f1 f1 f1 f1 00 00 00 00 00 00 00 d216f880: f2 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
d216f900: 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00
^ d216f980: f2 f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00 00 00 d216fa00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
After looking into this issue, I find the buggy address belongs to the task stack region. It seems KASAN has something wrong. I look into the code of __get_wchan in x86 architecture and find the same issue has been resolved by the commit f7d27c35ddff ("x86/mm, kasan: Silence KASAN warnings in get_wchan()"). The solution could be applied to powerpc architecture too.
As Andrey Ryabinin said, get_wchan() is racy by design, it may access volatile stack of running task, thus it may access redzone in a stack frame and cause KASAN to warn about this.
Use READ_ONCE_NOCHECK() to silence these warnings.
Reported-by: Wanming Hu huwanming@huaweil.com Signed-off-by: He Ying heying24@huawei.com Signed-off-by: Chen Jingwen chenjingwen6@huawei.com Reviewed-by: Kees Cook keescook@chromium.org Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20220121014418.155675-1-heying24@huawei.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/kernel/process.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 3064694afea1..cfb8fd76afb4 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -2108,12 +2108,12 @@ static unsigned long __get_wchan(struct task_struct *p) return 0;
do { - sp = *(unsigned long *)sp; + sp = READ_ONCE_NOCHECK(*(unsigned long *)sp); if (!validate_sp(sp, p, STACK_FRAME_OVERHEAD) || p->state == TASK_RUNNING) return 0; if (count > 0) { - ip = ((unsigned long *)sp)[STACK_FRAME_LR_SAVE]; + ip = READ_ONCE_NOCHECK(((unsigned long *)sp)[STACK_FRAME_LR_SAVE]); if (!in_sched_functions(ip)) return ip; }