Re: UBSAN: array-index-out-of-bounds in arch_uprobe_analyze_insn

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    325d0eab Merge branch 'akpm' (patches from Andrew)
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14e69c03900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b12e84189082991c
dashboard link: https://syzkaller.appspot.com/bug?extid=9b64b619f10f19d19a7c
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1573a8ad900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=164ee6c5900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9b64b619f10f19d19a7c@xxxxxxxxxxxxxxxxxxxxxxxxx

================================================================================
UBSAN: array-index-out-of-bounds in arch/x86/kernel/uprobes.c:263:56
index 4 is out of range for type 'insn_byte_t [4]'
CPU: 0 PID: 6870 Comm: syz-executor876 Not tainted 5.9.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x198/0x1fd lib/dump_stack.c:118
 ubsan_epilogue+0xb/0x5a lib/ubsan.c:148
 __ubsan_handle_out_of_bounds.cold+0x62/0x6c lib/ubsan.c:356
 is_prefix_bad arch/x86/kernel/uprobes.c:263 [inline]
 uprobe_init_insn arch/x86/kernel/uprobes.c:286 [inline]
 arch_uprobe_analyze_insn+0x8f4/0xa40 arch/x86/kernel/uprobes.c:856
 prepare_uprobe kernel/events/uprobes.c:860 [inline]
 install_breakpoint.isra.0+0x6c4/0x7c0 kernel/events/uprobes.c:903
 uprobe_mmap+0x5ec/0x1080 kernel/events/uprobes.c:1394
 mmap_region+0x5cf/0x1780 mm/mmap.c:1839
 do_mmap+0xcf9/0x11d0 mm/mmap.c:1545
 vm_mmap_pgoff+0x195/0x200 mm/util.c:506
 ksys_mmap_pgoff+0x444/0x580 mm/mmap.c:1596
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x440379
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffc6ed13058 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440379
RDX: 0000000000000000 RSI: 0000000000003000 RDI: 0000000020007000
RBP: 00000000006ca018 R08: 0000000000000003 R09: 0000000000000000
R10: 0000000000000412 R11: 0000000000000246 R12: 0000000000401b80
R13: 0000000000401c10 R14: 0000000000000000 R15: 0000000000000000
================================================================================