[PATCH V2] arm64: fix oops in concurrently setting insn_emulation sysctls

[Catalin Marinas]

On Sat, Jul 02, 2022 at 05:43:19AM +0000, haibinzhang(张海斌) wrote:
> How to reproduce:
>     launch two shell executions:
>        #!/bin/bash
>        while [ 1 ];
>        do
>            echo 1 > /proc/sys/abi/swp
>        done
> 
> Oops info:
>     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
> 
> emulation_proc_handler changes table->data for proc_dointvec_minmax
> and so it isn't allowed to reenter before restoring table->data,
> which isn't right now.
> 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.
> 
> Signed-off-by: hewenliang <hewenliang4 at huawei.com>
> Signed-off-by: Haibin Zhang <haibinzhang at tencent.com>

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>