Re: drm_mode_create_dumb_ioctl: divide error
From: David Herrmann
Date: Fri Aug 22 2014 - 06:38:55 EST
Hi
On Thu, Aug 21, 2014 at 8:18 PM, Tommi Rantala <tt.rantala@xxxxxxxxx> wrote:
> Hello,
>
> Triggered this while fuzzing v3.17-rc1-51-g372b1db with Trinity.
>
> Tommi
>
>
> [drm:drm_mode_legacy_fb_format] *ERROR* bad bpp, assuming x8r8g8b8 pixel format
> divide error: 0000 [#1] SMP DEBUG_PAGEALLOC
> CPU: 0 PID: 2854 Comm: trinity-c7 Not tainted 3.17.0-rc1+ #14
> Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> task: ffff88003926cac0 ti: ffff8800356b4000 task.ti: ffff8800356b4000
> RIP: 0010:[<ffffffff816688e3>] [<ffffffff816688e3>]
> drm_mode_create_dumb_ioctl+0x53/0xa0
> RSP: 0018:ffff8800356b7dc0 EFLAGS: 00010246
> RAX: 00000000ffffffff RBX: ffff88003545da68 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffff8800356b7e18 RDI: ffff88003d5c67b0
> RBP: ffff8800356b7dc8 R08: 0000000000000000 R09: 00000000ffffffff
> R10: 00000000ffffffff R11: ffffffff817f6d30 R12: 00000000000000b2
> R13: fffffffffffffff2 R14: ffff88003d5c67b0 R15: ffff88003545da68
> FS: 00007f06208fa700(0000) GS:ffff88003fa00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000001903108 CR3: 0000000036efa000 CR4: 00000000000006f0
> Stack:
> ffff8800356b7e18 ffff8800356b7ec8 ffffffff8165ac60 ffff8800356b7df8
> ffff8800356b7e18 ffff8800356b7e18 ffffffff824e1440 0000000000d52000
> 0000000000000020 00000000c02064b2 00000000fffffff2 ffffffffffffffff
> Call Trace:
> [<ffffffff8165ac60>] drm_ioctl+0x3b0/0x640
> [<ffffffff814b81b8>] ? avc_has_perm+0x218/0x2f0
> [<ffffffff814b7fc0>] ? avc_has_perm+0x20/0x2f0
> [<ffffffff81170bb8>] ? sched_clock_cpu+0xa8/0xf0
> [<ffffffff812922a0>] do_vfs_ioctl+0x4d0/0x510
> [<ffffffff814ba745>] ? selinux_file_ioctl+0xf5/0x100
> [<ffffffff8129232e>] SyS_ioctl+0x4e/0x80
> [<ffffffff822b10e9>] system_call_fastpath+0x16/0x1b
> Code: 55 41 b9 ff ff ff ff 41 83 c0 07 44 89 c8 41 c1 e8 03 48 89 e5
> 53 48 89 d3 31 d2 f7 f1 41 39 c0 77 46 41 0f af c8 31 d2 44 89 c8 <f7>
> f1 41 39 c2 77 36 41 0f af ca b8 ea ff ff ff 81 c1 ff 0f 00
> RIP [<ffffffff816688e3>] drm_mode_create_dumb_ioctl+0x53/0xa0
> RSP <ffff8800356b7dc0>
> ---[ end trace 6919129b71d9bf98 ]---
> [drm:drm_mode_legacy_fb_format] *ERROR* bad bpp, assuming x8r8g8b8 pixel format
>
>
>
> (gdb) list *0xffffffff816688e3
> 0xffffffff816688e3 is in drm_mode_create_dumb_ioctl
> (drivers/gpu/drm/drm_crtc.c:4703).
> 4698 /* overflow checks for 32bit size calculations */
> 4699 cpp = DIV_ROUND_UP(args->bpp, 8);
> 4700 if (cpp > 0xffffffffU / args->width)
> 4701 return -EINVAL;
> 4702 stride = cpp * args->width;
> 4703 if (args->height > 0xffffffffU / stride)
> 4704 return -EINVAL;
Hm, this doesn't make sense to me. args->bpp/width/height are
guaranteed to be non-zero and 32bit. Therefore, DIV_ROUND_UP() cannot
return 0 and "cpp" is thus non-zero. The overflow check makes sure
"cpp * args->width" cannot overflow, both are non-zero so "stride" is
non-zero and valid.
I cannot make much sense out of the x86 assembly below, so help welcome.
Thanks
David
> 4705
> 4706 /* test for wrap-around */
> 4707 size = args->height * stride;
> (gdb) disassemble drm_mode_create_dumb_ioctl
> Dump of assembler code for function drm_mode_create_dumb_ioctl:
> 0xffffffff81668890 <+0>: mov 0x20(%rdi),%rax
> 0xffffffff81668894 <+4>: mov 0x160(%rax),%r11
> 0xffffffff8166889b <+11>: test %r11,%r11
> 0xffffffff8166889e <+14>: je 0xffffffff8166890f
> <drm_mode_create_dumb_ioctl+127>
> 0xffffffff816688a0 <+16>: mov 0x4(%rsi),%ecx
> 0xffffffff816688a3 <+19>: test %ecx,%ecx
> 0xffffffff816688a5 <+21>: je 0xffffffff81668918
> <drm_mode_create_dumb_ioctl+136>
> 0xffffffff816688a7 <+23>: mov (%rsi),%r10d
> 0xffffffff816688aa <+26>: test %r10d,%r10d
> 0xffffffff816688ad <+29>: je 0xffffffff81668918
> <drm_mode_create_dumb_ioctl+136>
> 0xffffffff816688af <+31>: mov 0x8(%rsi),%r8d
> 0xffffffff816688b3 <+35>: test %r8d,%r8d
> 0xffffffff816688b6 <+38>: je 0xffffffff81668918
> <drm_mode_create_dumb_ioctl+136>
> 0xffffffff816688b8 <+40>: push %rbp
> 0xffffffff816688b9 <+41>: mov $0xffffffff,%r9d
> 0xffffffff816688bf <+47>: add $0x7,%r8d
> 0xffffffff816688c3 <+51>: mov %r9d,%eax
> 0xffffffff816688c6 <+54>: shr $0x3,%r8d
> 0xffffffff816688ca <+58>: mov %rsp,%rbp
> 0xffffffff816688cd <+61>: push %rbx
> 0xffffffff816688ce <+62>: mov %rdx,%rbx
> 0xffffffff816688d1 <+65>: xor %edx,%edx
> 0xffffffff816688d3 <+67>: div %ecx
> 0xffffffff816688d5 <+69>: cmp %eax,%r8d
> 0xffffffff816688d8 <+72>: ja 0xffffffff81668920
> <drm_mode_create_dumb_ioctl+144>
> 0xffffffff816688da <+74>: imul %r8d,%ecx
> 0xffffffff816688de <+78>: xor %edx,%edx
> 0xffffffff816688e0 <+80>: mov %r9d,%eax
> 0xffffffff816688e3 <+83>: div %ecx
> 0xffffffff816688e5 <+85>: cmp %eax,%r10d
> 0xffffffff816688e8 <+88>: ja 0xffffffff81668920
> <drm_mode_create_dumb_ioctl+144>
> 0xffffffff816688ea <+90>: imul %r10d,%ecx
> 0xffffffff816688ee <+94>: mov $0xffffffea,%eax
> 0xffffffff816688f3 <+99>: add $0xfff,%ecx
> 0xffffffff816688f9 <+105>: and $0xfffff000,%ecx
> 0xffffffff816688ff <+111>: je 0xffffffff81668928
> <drm_mode_create_dumb_ioctl+152>
> 0xffffffff81668901 <+113>: mov %rsi,%rdx
> 0xffffffff81668904 <+116>: mov %rdi,%rsi
> 0xffffffff81668907 <+119>: mov %rbx,%rdi
> 0xffffffff8166890a <+122>: callq *%r11
> 0xffffffff8166890d <+125>: jmp 0xffffffff81668928
> <drm_mode_create_dumb_ioctl+152>
> 0xffffffff8166890f <+127>: mov $0xffffffda,%eax
> 0xffffffff81668914 <+132>: retq
> 0xffffffff81668915 <+133>: nopl (%rax)
> 0xffffffff81668918 <+136>: mov $0xffffffea,%eax
> 0xffffffff8166891d <+141>: retq
> 0xffffffff8166891e <+142>: xchg %ax,%ax
> 0xffffffff81668920 <+144>: mov $0xffffffea,%eax
> 0xffffffff81668925 <+149>: nopl (%rax)
> 0xffffffff81668928 <+152>: pop %rbx
> 0xffffffff81668929 <+153>: pop %rbp
> 0xffffffff8166892a <+154>: retq
> End of assembler dump.
> (gdb)
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/