FROMGIT: arm64: fix oops in concurrently setting insn_emulation sysctls

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.

Bug: 237540956
Co-developed-by: hewenliang <[email protected]>
Signed-off-by: hewenliang <[email protected]>
Signed-off-by: Haibin Zhang <[email protected]>
Reviewed-by: Catalin Marinas <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>
[Lee: Added Fixes: tag]
(cherry picked from commit af483947d472eccb79e42059276c4deed76f99a6
git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/core)
Fixes: 587064b ("arm64: Add framework for legacy instruction emulation")
Signed-off-by: Lee Jones <[email protected]>
Change-Id: If9b96bb79c79903f9d8292e719b06fdef57ef1c5

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;