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Date: Fri, 10 Mar 2017 21:45:24 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Meelis Roos <mroos@linux.ee>
cc: Linux Kernel list <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>, kasan-dev@googlegroups.com
Subject: Re: UBSAN: Undefined behaviour in kernel/time/tick-sched.c:600:9
In-Reply-To: <alpine.LRH.2.20.1703101926520.21677@math.ut.ee>
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On Fri, 10 Mar 2017, Meelis Roos wrote:

Cc'ing KASAN folks

> (Retry with fixed address ox 86 list)
> 
> This HP Netserver LT6000R, quad P3 Xeon. Trying 
> 4.11.0-rc1-00088-gec3b93a, I got the following UBSAN warning that was 
> not there in 4.10:
> 
> [   14.820437] ================================================================================
> [   14.820534] UBSAN: Undefined behaviour in kernel/time/tick-sched.c:600:9
> [   14.820594] signed integer overflow:
> [   14.820645] 11567464533 + 3985952 cannot be represented in type 'long long int'

This does not make any sense:

     11567464533 + 3985952 = 0x2b1798055 + 0x3cd220 = 0x2b1b65275

which definitely fits into a 'long long int' aka 64 bit

> [   14.820722] CPU: 3 PID: 135 Comm: startpar Not tainted 4.11.0-rc1-00088-gec3b93a #61
> [   14.820793] Hardware name: Hewlett Packard HP NetServer/HP System Board, BIOS 4.06.46 PW 06/25/2003
> [   14.820863] Call Trace:
> [   14.820950]  ? dump_stack+0x45/0x6e
> [   14.821022]  ? ubsan_epilogue+0xb/0x40
> [   14.821081]  ? handle_overflow+0xb6/0xe0
> [   14.821146]  ? smp_trace_apic_timer_interrupt+0x85/0x100
> [   14.821208]  ? __ubsan_handle_add_overflow+0xf/0x20
> [   14.821281]  ? get_cpu_idle_time_us+0x204/0x2b0
> [   14.821350]  ? get_idle_time+0x57/0xb0
> [   14.821405]  ? show_stat+0x217/0x10c0
> [   14.821463]  ? seq_open+0x33/0xb0
> [   14.821519]  ? __d_alloc+0x149/0x2c0
> [   14.821574]  ? get_iowait_time+0xb0/0xb0
> [   14.821628]  ? single_open+0x4d/0xb0
> [   14.821685]  ? single_open_size+0x37/0xc0
> [   14.821748]  ? path_openat+0x7d5/0x1bd0
> [   14.821804]  ? seq_read+0xca/0x6f0
> [   14.821872]  ? _copy_to_user+0x5e/0x90
> [   14.821937]  ? cp_new_stat64+0x108/0x130
> [   14.821991]  ? __seq_open_private+0x80/0x80
> [   14.822062]  ? proc_reg_read+0x7c/0x120
> [   14.822117]  ? proc_reg_write+0x120/0x120
> [   14.822172]  ? __vfs_read+0x3e/0x240
> [   14.822228]  ? vfs_read+0x92/0x1b0
> [   14.822282]  ? SyS_read+0x45/0xa0
> [   14.822338]  ? do_fast_syscall_32+0xb9/0x220
> [   14.822395]  ? entry_SYSENTER_32+0x47/0x71
> [   14.822447] 
> ================================================================================
> 
> 
> -- 
> Meelis Roos (mroos@linux.ee)
>