[PATCH AUTOSEL 4.14 02/12] arm64: fix oops in concurrently setting insn_emulation sysctls

Sasha Levin
2022-08-08T01:59:26Z

From: haibinzhang (张海斌) <haibinzhang@tencent.com>

[ Upstream commit af483947d472eccb79e42059276c4deed76f99a6 ]

emulation_proc_handler() changes table->data for proc_dointvec_minmax
and can generate the following Oops if called concurrently with itself:

| Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010
| Internal error: Oops: 96000006 [#1] SMP
| Call trace:
| update_insn_emulation_mode+0xc0/0x148
| emulation_proc_handler+0x64/0xb8
| proc_sys_call_handler+0x9c/0xf8
| proc_sys_write+0x18/0x20
| __vfs_write+0x20/0x48
| vfs_write+0xe4/0x1d0
| ksys_write+0x70/0xf8
| __arm64_sys_write+0x20/0x28
| el0_svc_common.constprop.0+0x7c/0x1c0
| el0_svc_handler+0x2c/0xa0
| el0_svc+0x8/0x200

To fix this issue, keep the table->data as &insn->current_mode and
use container_of() to retrieve the insn pointer. Another mutex is
used to protect against the current_mode update but not for retrieving
insn_emulation as table->data is no longer changing.

Co-developed-by: hewenliang <hewenliang4@huawei.com>
Signed-off-by: hewenliang <hewenliang4@huawei.com>
Signed-off-by: Haibin Zhang <haibinzhang@tencent.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220128090324.2727688-1-hewenliang4@huawei.com
Link: https://lore.kernel.org/r/9A004C03-250B-46C5-BF39-782D7551B00E@tencent.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/kernel/armv8_deprecated.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c
index 092046704cbc..b82e32daaf66 100644
--- a/arch/arm64/kernel/armv8_deprecated.c
+++ b/arch/arm64/kernel/armv8_deprecated.c
@@ -63,6 +63,7 @@ struct insn_emulation {
static LIST_HEAD(insn_emulation);
static int nr_insn_emulated __initdata;
static DEFINE_RAW_SPINLOCK(insn_emulation_lock);
+static DEFINE_MUTEX(insn_emulation_mutex);

static void register_emulation_hooks(struct insn_emulation_ops *ops)
{
@@ -208,10 +209,10 @@ static int emulation_proc_handler(struct ctl_table *table, int write,
loff_t *ppos)
{
int ret = 0;
- struct insn_emulation *insn = (struct insn_emulation *) table->data;
+ struct insn_emulation *insn = container_of(table->data, struct insn_emulation, current_mode);
enum insn_emulation_mode prev_mode = insn->current_mode;

- table->data = &insn->current_mode;
+ mutex_lock(&insn_emulation_mutex);
ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);

if (ret || !write || prev_mode == insn->current_mode)
@@ -224,7 +225,7 @@ static int emulation_proc_handler(struct ctl_table *table, int write,
update_insn_emulation_mode(insn, INSN_UNDEF);
}
ret:
- table->data = insn;
+ mutex_unlock(&insn_emulation_mutex);
return ret;
}

@@ -254,7 +255,7 @@ static void __init register_insn_emulation_sysctl(struct ctl_table *table)
sysctl->maxlen = sizeof(int);

sysctl->procname = insn->ops->name;
- sysctl->data = insn;
+ sysctl->data = &insn->current_mode;
sysctl->extra1 = &insn->min;
sysctl->extra2 = &insn->max;
sysctl->proc_handler = emulation_proc_handler;
--
2.35.1