[v5.15] BUG: unable to handle kernel paging request in fb_videomode_to_var

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f7347f400572 Linux 5.15.180
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=14a11374580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9a44713381e9503a
dashboard link: https://syzkaller.appspot.com/bug?extid=5f0d5cd0f34d4276a2eb
compiler: Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2
userspace arch: arm64

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/57026a6111ba/disk-f7347f40.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/73b19340e28e/vmlinux-f7347f40.xz
kernel image: https://storage.googleapis.com/syzbot-assets/bb6b489b9de3/Image-f7347f40.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5f0d5c...@syzkaller.appspotmail.com

Unable to handle kernel paging request at virtual address dfff800000000001
Mem abort info:
ESR = 0x0000000096000006
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x06: level 2 translation fault
Data abort info:
ISV = 0, ISS = 0x00000006
CM = 0, WnR = 0
[dfff800000000001] address between user and kernel address ranges
Internal error: Oops: 0000000096000006 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 4230 Comm: syz.4.37 Not tainted 5.15.180-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : fb_videomode_to_var+0x3c/0x638 drivers/video/fbdev/core/modedb.c:901
lr : fb_videomode_to_var+0x2c/0x638 drivers/video/fbdev/core/modedb.c:900
sp : ffff80001fb17640
x29: ffff80001fb17650 x28: ffff70000282a1c0 x27: 00000000000000f8
x26: ffff0000cb05a000 x25: ffff0000caf055a0 x24: ffff80001fb17700
x23: ffff800014150e00 x22: 0000000000000000 x21: dfff800000000000
x20: 0000000000000000 x19: ffff80001fb17700 x18: 0000000000000000
x17: 0000000000000002 x16: ffff80000acbd360 x15: 0000000000000004
x14: 0000000000ff0100 x13: ffffffffffffffff x12: 0000000000080000
x11: 0000000000004a24 x10: 0000000000000007 x9 : 0000000000000001
x8 : 000000000000000c x7 : 0000000000000000 x6 : 000000000000003f
x5 : 0000000000000040 x4 : 0000000000000000 x3 : 0000000000000020
x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff80001fb17700
Call trace:
fb_videomode_to_var+0x3c/0x638 drivers/video/fbdev/core/modedb.c:901
display_to_var drivers/video/fbdev/core/fbcon.c:921 [inline]
fbcon_switch+0x458/0x19ac drivers/video/fbdev/core/fbcon.c:2111
redraw_screen+0x4c0/0xcb8 drivers/tty/vt/vt.c:1021
fbcon_modechanged+0x87c/0xe4c drivers/video/fbdev/core/fbcon.c:2719
fbcon_update_vcs+0x3c/0x4c drivers/video/fbdev/core/fbcon.c:2764
do_fb_ioctl+0xaf0/0xcb0 drivers/video/fbdev/core/fbmem.c:1130
fb_ioctl+0xec/0x134 drivers/video/fbdev/core/fbmem.c:1205
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
el0_svc+0x78/0x1e0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0xcc/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584
Code: 91003288 d343fd09 1200090a 11000d4a (38f56929)
---[ end trace 31b150cc47c218db ]---
----------------
Code disassembly (best guess):
0: 91003288 add x8, x20, #0xc
4: d343fd09 lsr x9, x8, #3
8: 1200090a and w10, w8, #0x7
c: 11000d4a add w10, w10, #0x3
* 10: 38f56929 ldrsb w9, [x9, x21] <-- trapping instruction


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: f7347f400572 Linux 5.15.180
git tree: linux-5.15.y

console output: https://syzkaller.appspot.com/x/log.txt?x=171e9368580000

kernel config: https://syzkaller.appspot.com/x/.config?x=9a44713381e9503a
dashboard link: https://syzkaller.appspot.com/bug?extid=5f0d5cd0f34d4276a2eb
compiler: Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2
userspace arch: arm64

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=139608d4580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16e93374580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/57026a6111ba/disk-f7347f40.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/73b19340e28e/vmlinux-f7347f40.xz
kernel image: https://storage.googleapis.com/syzbot-assets/bb6b489b9de3/Image-f7347f40.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5f0d5c...@syzkaller.appspotmail.com

__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
el0_svc+0x78/0x1e0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0xcc/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

Unable to handle kernel paging request at virtual address dfff800000000001
Mem abort info:
ESR = 0x0000000096000006
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x06: level 2 translation fault
Data abort info:
ISV = 0, ISS = 0x00000006
CM = 0, WnR = 0
[dfff800000000001] address between user and kernel address ranges
Internal error: Oops: 0000000096000006 [#1] PREEMPT SMP
Modules linked in:

CPU: 0 PID: 4023 Comm: syz-executor326 Not tainted 5.15.180-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : fb_videomode_to_var+0x3c/0x638 drivers/video/fbdev/core/modedb.c:901
lr : fb_videomode_to_var+0x2c/0x638 drivers/video/fbdev/core/modedb.c:900

sp : ffff80001f297420
x29: ffff80001f297430 x28: ffff70000282a1c0 x27: 00000000000000f8
x26: ffff0000cb04b000 x25: ffff0000cb07c5a0 x24: ffff80001f2974e0

x23: ffff800014150e00 x22: 0000000000000000 x21: dfff800000000000

x20: 0000000000000000 x19: ffff80001f2974e0 x18: 0000000000000000
x17: 0000000000000000 x16: ffff80000acbd360 x15: 0000000000000004
x14: 0000000000ff0100 x13: 0000000000000000 x12: 0000000000ff0100
x11: 0000000000000000 x10: 0000000000000007 x9 : 0000000000000001

x8 : 000000000000000c x7 : 0000000000000000 x6 : 000000000000003f

x5 : 0000000000000040 x4 : ffffffffffffffe0 x3 : 0000000000000080
x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff80001f2974e0

Call trace:
fb_videomode_to_var+0x3c/0x638 drivers/video/fbdev/core/modedb.c:901
display_to_var drivers/video/fbdev/core/fbcon.c:921 [inline]
fbcon_switch+0x458/0x19ac drivers/video/fbdev/core/fbcon.c:2111
redraw_screen+0x4c0/0xcb8 drivers/tty/vt/vt.c:1021

vc_do_resize+0xc2c/0x10e0 drivers/tty/vt/vt.c:1342
vc_resize+0x54/0x68 drivers/tty/vt/vt.c:1362
fbcon_modechanged+0x5ac/0xe4c drivers/video/fbdev/core/fbcon.c:2708

fbcon_update_vcs+0x3c/0x4c drivers/video/fbdev/core/fbcon.c:2764
do_fb_ioctl+0xaf0/0xcb0 drivers/video/fbdev/core/fbmem.c:1130
fb_ioctl+0xec/0x134 drivers/video/fbdev/core/fbmem.c:1205
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
el0_svc+0x78/0x1e0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0xcc/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584
Code: 91003288 d343fd09 1200090a 11000d4a (38f56929)

---[ end trace a8d45f90bbd014fb ]---

----------------
Code disassembly (best guess):
0: 91003288 add x8, x20, #0xc
4: d343fd09 lsr x9, x8, #3
8: 1200090a and w10, w8, #0x7
c: 11000d4a add w10, w10, #0x3
* 10: 38f56929 ldrsb w9, [x9, x21] <-- trapping instruction


---

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[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.