On Thu, Jun 01 2023 at 20:38, syzbot wrote:
> general protection fault, probably for non-canonical address 0xdffffc0040000033: 0000 [#1] PREEMPT SMP KASAN
> KASAN: probably user-memory-access in range [0x0000000200000198-0x000000020000019f]
> CPU: 1 PID: 262216 Comm: Not tainted 6.4.0-rc2-next-20230515-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/25/2023
> RIP: 0010:get_running_cputimer include/linux/sched/cputime.h:79 [inline]
> RIP: 0010:account_group_system_time include/linux/sched/cputime.h:143 [inline]
> RIP: 0010:account_system_index_time+0x86/0x2f0 kernel/sched/cputime.c:173
> Code: 63 02 00 00 48 8b 9d f8 08 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d bb 98 01 00 00 4c 8d b3 38 01 00 00 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e e7 01 00 00 8b 83 98 01 00 00
> RSP: 0018:ffffc900001e0da0 EFLAGS: 00010006
> RAX: dffffc0000000000 RBX: 0000000200000001 RCX: 1ffffffff1827d41
> RDX: 0000000040000033 RSI: 000000000097fff6 RDI: 0000000200000199
> RBP: ffff88807638bb80 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000000 R11: ffffffffffffffff R12: 000000000097fff6
> R13: 0000000000000002 R14: 0000000200000139 R15: ffffffff817770e0
> FS: 00005555556c1300(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ffca0efd000 CR3: 0000000019395000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <IRQ>
> update_process_times+0x26/0x1a0 kernel/time/timer.c:2069
> tick_sched_handle+0x8e/0x170 kernel/time/tick-sched.c:243
> tick_sched_timer+0xee/0x110 kernel/time/tick-sched.c:1481
> __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
> __hrtimer_run_queues+0x1c0/0xa30 kernel/time/hrtimer.c:1749
> hrtimer_interrupt+0x320/0x7b0 kernel/time/hrtimer.c:1811
> local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1095 [inline]
> __sysvec_apic_timer_interrupt+0x14a/0x430 arch/x86/kernel/apic/apic.c:1112
> sysvec_apic_timer_interrupt+0x92/0xc0 arch/x86/kernel/apic/apic.c:1106
> </IRQ>
> RSP: 0018:ffffc900001e0da0 EFLAGS: 00010006
> RAX: dffffc0000000000 RBX: 0000000200000001 RCX: 1ffffffff1827d41
> RDX: 0000000040000033 RSI: 000000000097fff6 RDI: 0000000200000199
> RBP: ffff88807638bb80 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000000 R11: ffffffffffffffff R12: 000000000097fff6
> R13: 0000000000000002 R14: 0000000200000139 R15: ffffffff817770e0
> FS: 00005555556c1300(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ffca0efd000 CR3: 0000000019395000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Code disassembly (best guess):
I built with that config and stared at the disassembly.
RBP contains the task pointer, which looks valid RBP: ffff88807638bb80
> 4: 48 8b 9d f8 08 00 00 mov 0x8f8(%rbp),%rbx
struct signal_struct * signal; /* 2296 8 */
2296 == 0x8f8
So this loads tsk->signal into RBX
RBX: 0000000200000001
which is clearly not a valid signal_struct pointer...
The rest is a consequence of this.
> b: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
> 12: fc ff df
> 15: 48 8d bb 98 01 00 00 lea 0x198(%rbx),%rdi
> 1c: 4c 8d b3 38 01 00 00 lea 0x138(%rbx),%r14
> 23: 48 89 fa mov %rdi,%rdx
> 26: 48 c1 ea 03 shr $0x3,%rdx
> * 2a: 0f b6 04 02 movzbl (%rdx,%rax,1),%eax <-- trapping instruction
> 2e: 84 c0 test %al,%al
> 30: 74 08 je 0x3a
> 32: 3c 03 cmp $0x3,%al
> 34: 0f 8e e7 01 00 00 jle 0x221
> 3a: 8b 83 98 01 00 00 mov 0x198(%rbx),%eax
Looks like good old memory corruption. tsk->comm looks weird too:
> CPU: 1 PID: 262216 Comm: Not tainted 6.4.0-rc2-next-20230515-syzkaller #0
tsk>comm is at offset 0x898 so close enough to the corrupted
tsk->signal.
I let the reiserfs wizards decode the root cause :)
Thanks,
tglx
