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 181c29af5617..7c69a203cdf8 100644 --- a/arch/arm64/kernel/armv8_deprecated.c +++ b/arch/arm64/kernel/armv8_deprecated.c @@ -62,6 +62,7 @@ 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) { @@ -210,10 +211,10 @@ 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) @@ -226,7 +227,7 @@ 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; }
@@ -250,7 +251,7 @@ static void __init register_insn_emulation_sysctl(void) 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;