[PATCH 5.15 395/917] scs: Release kasan vmalloc poison in scs_free process

Greg Kroah-Hartman
2021-11-15T23:38:31Z

From: Yee Lee <yee.lee@mediatek.com>

[ Upstream commit 528a4ab45300fa6283556d9b48e26b45a8aa15c4 ]

Since scs allocation is moved to vmalloc region, the
shadow stack is protected by kasan_posion_vmalloc.
However, the vfree_atomic operation needs to access
its context for scs_free process and causes kasan error
as the dump info below.

This patch Adds kasan_unpoison_vmalloc() before vfree_atomic,
which aligns to the prior flow as using kmem_cache.
The vmalloc region will go back posioned in the following
vumap() operations.

==================================================================
BUG: KASAN: vmalloc-out-of-bounds in llist_add_batch+0x60/0xd4
Write of size 8 at addr ffff8000100b9000 by task kthreadd/2

CPU: 0 PID: 2 Comm: kthreadd Not tainted 5.15.0-rc2-11681-g92477dd1faa6-dirty #1
Hardware name: linux,dummy-virt (DT)
Call trace:
dump_backtrace+0x0/0x43c
show_stack+0x1c/0x2c
dump_stack_lvl+0x68/0x84
print_address_description+0x80/0x394
kasan_report+0x180/0x1dc
__asan_report_store8_noabort+0x48/0x58
llist_add_batch+0x60/0xd4
vfree_atomic+0x60/0xe0
scs_free+0x1dc/0x1fc
scs_release+0xa4/0xd4
free_task+0x30/0xe4
__put_task_struct+0x1ec/0x2e0
delayed_put_task_struct+0x5c/0xa0
rcu_do_batch+0x62c/0x8a0
rcu_core+0x60c/0xc14
rcu_core_si+0x14/0x24
__do_softirq+0x19c/0x68c
irq_exit+0x118/0x2dc
handle_domain_irq+0xcc/0x134
gic_handle_irq+0x7c/0x1bc
call_on_irq_stack+0x40/0x70
do_interrupt_handler+0x78/0x9c
el1_interrupt+0x34/0x60
el1h_64_irq_handler+0x1c/0x2c
el1h_64_irq+0x78/0x7c
_raw_spin_unlock_irqrestore+0x40/0xcc
sched_fork+0x4f0/0xb00
copy_process+0xacc/0x3648
kernel_clone+0x168/0x534
kernel_thread+0x13c/0x1b0
kthreadd+0x2bc/0x400
ret_from_fork+0x10/0x20

Memory state around the buggy address:
ffff8000100b8f00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
ffff8000100b8f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>ffff8000100b9000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
^
ffff8000100b9080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
ffff8000100b9100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
==================================================================

Suggested-by: Kuan-Ying Lee <kuan-ying.lee@mediatek.com>
Acked-by: Will Deacon <will@kernel.org>
Tested-by: Will Deacon <will@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Yee Lee <yee.lee@mediatek.com>
Fixes: a2abe7cbd8fe ("scs: switch to vmapped shadow stacks")
Link: https://lore.kernel.org/r/20210930081619.30091-1-yee.lee@mediatek.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/scs.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/kernel/scs.c b/kernel/scs.c
index e2a71fc82fa06..579841be88646 100644
--- a/kernel/scs.c
+++ b/kernel/scs.c
@@ -78,6 +78,7 @@ void scs_free(void *s)
if (this_cpu_cmpxchg(scs_cache[i], 0, s) == NULL)
return;

+ kasan_unpoison_vmalloc(s, SCS_SIZE);
vfree_atomic(s);
}

--
2.33.0