[Qemu-devel] [Bug 1813201] [NEW] QEMU TCG i386 / x86_64 system emulation crash when executing int instruction

[Alberto Ortega]

Public bug reported:

QEMU version:
-------------

qemu from git, master branch commit
d058a37a6e8daa8d71a6f2b613eb415b69363755

Release versions are also affected.

Summary:
--------

QEMU i386 and x86_64 system emulation crash when executing the following
"int" instruction:

cd08  int 8

This generates a kernel NULL pointer dereference error in Linux, and a
BSOD error in Windows.

No special permissions are required to execute the instruction, any
unprivileged user can execute it.

This issue has been reproduced in QEMU running in TCG mode. KVM is not
affected.

Kernel panic log:

[  111.091138] BUG: unable to handle kernel NULL pointer dereference at 00000014
[  111.092145] IP: [<ce0513ad>] doublefault_fn+0xd/0x130
[  111.092145] *pdpt = 0000000000000000 *pde = f000ff53f000ff53 [  111.092145] 
[  111.092145] Oops: 0000 [#1] SMP
[  111.092145] Modules linked in: kvm_amd bochs_drm ppdev ttm drm_kms_helper 
drm kvm irqbypass evdev pcspkr serio_raw sg parport_pc parport button ip_tables 
x_tables autofs4 ext4 crc16 jbd2 crc32c_generic fscrypto ecb xts lrw gf128mul 
ablk_helper cryptd aes_i586 mbcache sr_mod sd_mod cdrom ata_generic ata_piix 
libata psmouse e1000 scsi_mod i2c_piix4 floppy
[  111.092145] CPU: 0 PID: 409 Comm: int8.elf Not tainted 4.9.0-8-686-pae #1 
Debian 4.9.130-2
[  111.092145] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
rel-1.12.0-0-ga698c8995f-prebuilt.qemu.org 04/01/2014
[  111.092145] task: f6c88a80 task.stack: f6e52000
[  111.092145] EIP: 0060:[<ce0513ad>] EFLAGS: 00004086 CPU: 0
[  111.092145] EIP is at doublefault_fn+0xd/0x130
[  111.092145] EAX: 00000000 EBX: 00000000 ECX: 00000000 EDX: 00000000
[  111.092145] ESI: 00000000 EDI: 00000000 EBP: ce8f13fc ESP: ce8f13d4
[  111.092145]  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
[  111.092145] CR0: 8005003b CR2: 00000014 CR3: 0e8e1000 CR4: 000006f0
[  111.092145] Stack:
[  111.092145]  00000000 00000000 00000000 00000000 00000000 00000000 00000000 
00000000
[  111.092145]  00000000 00000000 00000000 00000000 00000000 00000000 00000000 
00000000
[  111.092145]  00000000 00000000 00000000 00000000 fed00000 ce474ad0 00000000 
00017d78
[  111.092145] Call Trace:
[  111.092145] Code: 86 fd ff eb a3 89 f6 8d bc 27 00 00 00 00 55 89 e5 3e 8d 
74 26 00 5d e9 e2 79 fd ff 66 90 55 89 e5 56 53 83 ec 20 3e 8d 74 26 00 <65> a1 
14 00 00 00 89 45 f4 31 c0 31 c0 c7 45 f0 00 00 00 00 66
[  111.092145] EIP: [<ce0513ad>] [  111.092145] doublefault_fn+0xd/0x130
[  111.092145]  SS:ESP 0068:ce8f13d4
[  111.092145] CR2: 0000000000000014
[  111.092145] ---[ end trace 8afa7884b76cafc1 ]---

Testcase:
---------

void main() {
        asm("int $0x8");
}

** Affects: qemu
     Importance: Undecided
         Status: New


** Tags: tcg

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https://bugs.launchpad.net/bugs/1813201

Title:
  QEMU TCG i386 / x86_64 system emulation crash when executing int
  instruction

Status in QEMU:
  New

Bug description:
  QEMU version:
  -------------

  qemu from git, master branch commit
  d058a37a6e8daa8d71a6f2b613eb415b69363755

  Release versions are also affected.

  Summary:
  --------

  QEMU i386 and x86_64 system emulation crash when executing the
  following "int" instruction:

  cd08  int 8

  This generates a kernel NULL pointer dereference error in Linux, and a
  BSOD error in Windows.

  No special permissions are required to execute the instruction, any
  unprivileged user can execute it.

  This issue has been reproduced in QEMU running in TCG mode. KVM is not
  affected.

  Kernel panic log:

  [  111.091138] BUG: unable to handle kernel NULL pointer dereference at 
00000014
  [  111.092145] IP: [<ce0513ad>] doublefault_fn+0xd/0x130
  [  111.092145] *pdpt = 0000000000000000 *pde = f000ff53f000ff53 [  
111.092145] 
  [  111.092145] Oops: 0000 [#1] SMP
  [  111.092145] Modules linked in: kvm_amd bochs_drm ppdev ttm drm_kms_helper 
drm kvm irqbypass evdev pcspkr serio_raw sg parport_pc parport button ip_tables 
x_tables autofs4 ext4 crc16 jbd2 crc32c_generic fscrypto ecb xts lrw gf128mul 
ablk_helper cryptd aes_i586 mbcache sr_mod sd_mod cdrom ata_generic ata_piix 
libata psmouse e1000 scsi_mod i2c_piix4 floppy
  [  111.092145] CPU: 0 PID: 409 Comm: int8.elf Not tainted 4.9.0-8-686-pae #1 
Debian 4.9.130-2
  [  111.092145] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
rel-1.12.0-0-ga698c8995f-prebuilt.qemu.org 04/01/2014
  [  111.092145] task: f6c88a80 task.stack: f6e52000
  [  111.092145] EIP: 0060:[<ce0513ad>] EFLAGS: 00004086 CPU: 0
  [  111.092145] EIP is at doublefault_fn+0xd/0x130
  [  111.092145] EAX: 00000000 EBX: 00000000 ECX: 00000000 EDX: 00000000
  [  111.092145] ESI: 00000000 EDI: 00000000 EBP: ce8f13fc ESP: ce8f13d4
  [  111.092145]  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
  [  111.092145] CR0: 8005003b CR2: 00000014 CR3: 0e8e1000 CR4: 000006f0
  [  111.092145] Stack:
  [  111.092145]  00000000 00000000 00000000 00000000 00000000 00000000 
00000000 00000000
  [  111.092145]  00000000 00000000 00000000 00000000 00000000 00000000 
00000000 00000000
  [  111.092145]  00000000 00000000 00000000 00000000 fed00000 ce474ad0 
00000000 00017d78
  [  111.092145] Call Trace:
  [  111.092145] Code: 86 fd ff eb a3 89 f6 8d bc 27 00 00 00 00 55 89 e5 3e 8d 
74 26 00 5d e9 e2 79 fd ff 66 90 55 89 e5 56 53 83 ec 20 3e 8d 74 26 00 <65> a1 
14 00 00 00 89 45 f4 31 c0 31 c0 c7 45 f0 00 00 00 00 66
  [  111.092145] EIP: [<ce0513ad>] [  111.092145] doublefault_fn+0xd/0x130
  [  111.092145]  SS:ESP 0068:ce8f13d4
  [  111.092145] CR2: 0000000000000014
  [  111.092145] ---[ end trace 8afa7884b76cafc1 ]---

  Testcase:
  ---------

  void main() {
          asm("int $0x8");
  }

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