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To:     linux-kernel@vger.kernel.org
From:   Strontium <strntydog@gmail.com>
Subject: mips32r2 kexec load is panicking kernel 5.4 and 5.10
Message-ID: <447fc6f7-dd36-7cfd-dd87-645ed57cec90@gmail.com>
Date:   Tue, 22 Jun 2021 21:59:29 +0700
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When i execute a kexec -l (load, not execute) on my MT7621 (mips32r2)
target running either the 5.4 or 5.10 kernel, i am getting a reported
kernel bug that causes the kernel to panic and reboot.  The error is the
same on either 5.4 or 5.10.  My target runs from flash, and the kernel i
am trying to kexec is the exact same kernel booted from flash.

# kexec -l --append="console=ttyS0,115200 rootfstype=squashfs"
/tmp/vmlinux.elf
Modified cmdline:console=ttyS0,115200 rootfstype=squashfs
Unable to find /proc/device-tree/chosen/[linux,]stdout-path, printing
from purgatory is disabled
[  761.663355] kexec command line truncated to 256 bytes
[  761.668452] usercopy: Kernel memory overwrite attempt detected to
kernel text (offset 81844, size 256)!
[  761.677856] Kernel bug detected[#1]:
[  761.681423] CPU: 2 PID: 1755 Comm: kexec Not tainted 5.10.43 #0
[  761.687317] $ 0   : 00000000 00000001 0000005b 00988000
[  761.692545] $ 4   : 805e4408 8101e378 810238f8 822e1ca8
[  761.697770] $ 8   : 00000001 822e1cc0 00000000 000019c8
[  761.702991] $12   : 74206465 ffffff7f 00000001 656b206f
[  761.708214] $16   : 800153b4 00000100 00000000 800154b4
[  761.713435] $20   : 0041e02c 80010000 00000000 00000000
[  761.718656] $24   : 00000000 80314988                 
[  761.723877] $28   : 822e0000 822e1e50 80650000 801507e8
[  761.729100] Hi    : 00000125
[  761.731964] Lo    : 122f2000
[  761.734845] epc   : 801507e8 usercopy_abort+0x94/0x98
[  761.739886] ra    : 801507e8 usercopy_abort+0x94/0x98
[  761.744913] Status: 1100fc03 KERNEL EXL IE
[  761.749097] Cause : 50800024 (ExcCode 09)
[  761.753086] PrId  : 0001992f (MIPS 1004Kc)
[  761.757161] Modules linked in: mt7915e mt76 mac80211 cfg80211 hwmon
crc_ccitt compat sha256_generic libsha256 seqiv jitterentropy_rng drbg
hmac cmac leds_gpio gpio_button_hotplug zram zsmalloc
[  761.774316] Process kexec (pid: 1755, threadinfo=c9ceaefe,
task=a03f7798, tls=77ef2ec8)
[  761.782284] Stack : 00000100 80568ddc 805b702c 80568f04 8055f414
8055f414 8055f414 00013fb4
[  761.790642]         00000100 8237ce00 00000100 80150940 822e1eb4
80010000 0041e02c 80069818
[  761.798997]         00000100 8237ce00 38e38e39 00000100 80015388
8237ce00 80010000 80014cb8
[  761.807354]         822e1eb0 00000100 00000006 8054f4ba 8237ce00
00000000 807c8ee0 8237ce20
[  761.815709]         00000000 00000003 00000000 800a4498 00000000
8012a078 00000000 815ba758
[  761.824061]         ...
[  761.826505] Call Trace:
[  761.828944] [<801507e8>] usercopy_abort+0x94/0x98
[  761.833632] [<80150940>] __check_object_size+0x154/0x1c4
[  761.838945] [<80014cb8>] machine_kexec_prepare+0x124/0x2c4
[  761.844430] [<800a4498>] sys_kexec_load+0x258/0x388
[  761.849293] [<800135f8>] syscall_common+0x34/0x58
[  761.853980]
[  761.855461] Code: afa30010  0c01a5fe  24848e80 <000c000d> 3c02805d 
8c4293fc  1c40006c  00000000  27bdffd0
[  761.865209]
[  761.866973] ---[ end trace 8145ef41fc12390f ]---
[  761.871748] Kernel panic - not syncing: Fatal exception
[  761.876984] Rebooting in 3 seconds..

Is this a problem with the kexec utility from kexec-tools or is it a
kernel bug, as it appears to be?  Or have i done something wrong?

Steven