qemu-3.1.0-rc0: tcg.c crash in temp_load

[Alberto Ortega]

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

qemu-3.1.0-rc0 compiled from sources (earlier versions also affected)

Summary:
--------

TCG crashes in i386 and x86_64 when it tries to execute some specific illegal instructions. When running full OS emulation, both the guest system and QEMU crash.

The issue has been reproduced in two scenarios:

Ubuntu x64 host running Debian x86 guest with the following command line: qemu-system-x86_64 -m 4G debian.qcow

When the attached ELF file is executed inside the guest, QEMU crashes.

It can also be reproduced from the command line:

$ qemu-i386 tcg_crash.elf
/home/alberto/Documents/qemu-3.1.0-rc0/tcg/tcg.c:2863: tcg fatal error
qemu: uncaught target signal 11 (Segmentation fault) - core dumped
zsh: segmentation fault (core dumped) ../qemu-3.1.0-rc0/build/i386-linux-user/qemu-i386 tcg_crash.elf

GDB backtrace:

(gdb) bt
#0 0x0000000060206488 in raise ()
#1 0x0000000060206b8a in abort ()
#2 0x0000000060007016 in temp_load (s=s@entry=0x607a2780 <tcg_init_ctx>, ts=ts@entry=0x607a3178 <tcg_init_ctx+2552>, desired_regs=<optimized out>, allocated_regs=allocated_regs@entry=16400)
    at /home/alberto/Documents/qemu-3.1.0-rc0/tcg/tcg.c:2863
#3 0x000000006000a4d9 in tcg_reg_alloc_op (op=0x62808c20, s=<optimized out>) at /home/alberto/Documents/qemu-3.1.0-rc0/tcg/tcg.c:3070
#4 tcg_gen_code (s=<optimized out>, tb=tb@entry=0x607ac040 <static_code_gen_buffer+4144>) at /home/alberto/Documents/qemu-3.1.0-rc0/tcg/tcg.c:3598
#5 0x000000006003ef9a in tb_gen_code (cpu=cpu@entry=0x627e0010, pc=pc@entry=134512724, cs_base=cs_base@entry=0, flags=flags@entry=4194483, cflags=cflags@entry=0)
    at /home/alberto/Documents/qemu-3.1.0-rc0/accel/tcg/translate-all.c:1752
#6 0x000000006003d979 in tb_find (cf_mask=0, tb_exit=0, last_tb=0x0, cpu=0x0) at /home/alberto/Documents/qemu-3.1.0-rc0/accel/tcg/cpu-exec.c:404
#7 cpu_exec (cpu=cpu@entry=0x627e0010) at /home/alberto/Documents/qemu-3.1.0-rc0/accel/tcg/cpu-exec.c:724
#8 0x000000006006e1a0 in cpu_loop (env=env@entry=0x627e82c0) at /home/alberto/Documents/qemu-3.1.0-rc0/linux-user/i386/cpu_loop.c:93
#9 0x00000000600037c5 in main (argc=2, argv=0x7fffffffdd28, envp=<optimized out>) at /home/alberto/Documents/qemu-3.1.0-rc0/linux-user/main.c:819
(gdb)

Testcase:
---------

Find ELF file attached.

[Alex Bennée (ajbennee)]

Can you please re-test on the current master, I think this was fixed by:

commit e84fcd7f662a0d8198703f6f89416d7ac2c32767
Author: Richard Henderson <email address hidden>
Date: Tue Nov 13 20:35:10 2018 +0100

    target/i386: Generate #UD when applying LOCK to a register destination

Testing on my box:

12:14:20 [alex@idun:~/l/qemu.git] master + ./i386-linux-user/qemu-i386 ~/tcg_crash.elf
qemu: uncaught target signal 4 (Illegal instruction) - core dumped
fish: “./i386-linux-user/qemu-i386 ~/t…” terminated by signal SIGILL (Illegal instruction)

[Alberto Ortega (aortega)]

I've tested this again and I haven't been able to reproduce it anymore on the current master, it looks fixed.

Thanks! :)

[Alberto Ortega (aortega)]

Hello again,

After more testing I've been able to trigger this bug again using qemu from git master. Find attached a new ELF that will reproduce the problem:

$ qemu-i386 tcg_crash1.elf
/home/alberto/Documents/qemu/tcg/tcg.c:2863: tcg fatal error
qemu: uncaught target signal 11 (Segmentation fault) - core dumped
zsh: segmentation fault (core dumped) ./qemu/build/i386-linux-user/qemu-i386 tcg_crash1.elf

Invalid instructions:

f0 invalid
40 inc eax
a7 cmpsd dword [esi], dword ptr es:[edi]
48 dec eax

GDB backtrace is the same as before.

[Richard Henderson (rth)]

This second crash is of course a different bug.

[Philippe Mathieu-Daudé (philmd)]

Hi Alberto,

Can you open another ticket for your new bug?

Thanks.

On Fri, Dec 7, 2018 at 6:22 PM Richard Henderson <email address hidden> wrote:
>
> This second crash is of course a different bug.
>
> --
> You received this bug notification because you are a member of qemu-
> devel-ml, which is subscribed to QEMU.
> https://bugs.launchpad.net/bugs/1803160
>
> Title:
> qemu-3.1.0-rc0: tcg.c crash in temp_load
>
> Status in QEMU:
> Fix Committed
>
> Bug description:
> QEMU version:
> -------------
>
> qemu-3.1.0-rc0 compiled from sources (earlier versions also affected)
>
> Summary:
> --------
>
> TCG crashes in i386 and x86_64 when it tries to execute some specific
> illegal instructions. When running full OS emulation, both the guest
> system and QEMU crash.
>
> The issue has been reproduced in two scenarios:
>
> Ubuntu x64 host running Debian x86 guest with the following command
> line: qemu-system-x86_64 -m 4G debian.qcow
>
> When the attached ELF file is executed inside the guest, QEMU crashes.
>
> It can also be reproduced from the command line:
>
> $ qemu-i386 tcg_crash.elf
> /home/alberto/Documents/qemu-3.1.0-rc0/tcg/tcg.c:2863: tcg fatal error
> qemu: uncaught target signal 11 (Segmentation fault) - core dumped
> zsh: segmentation fault (core dumped) ../qemu-3.1.0-rc0/build/i386-linux-user/qemu-i386 tcg_crash.elf
>
> GDB backtrace:
>
> (gdb) bt
> #0 0x0000000060206488 in raise ()
> #1 0x0000000060206b8a in abort ()
> #2 0x0000000060007016 in temp_load (s=s@entry=0x607a2780 <tcg_init_ctx>, ts=ts@entry=0x607a3178 <tcg_init_ctx+2552>, desired_regs=<optimized out>, allocated_regs=allocated_regs@entry=16400)
> at /home/alberto/Documents/qemu-3.1.0-rc0/tcg/tcg.c:2863
> #3 0x000000006000a4d9 in tcg_reg_alloc_op (op=0x62808c20, s=<optimized out>) at /home/alberto/Documents/qemu-3.1.0-rc0/tcg/tcg.c:3070
> #4 tcg_gen_code (s=<optimized out>, tb=tb@entry=0x607ac040 <static_code_gen_buffer+4144>) at /home/alberto/Documents/qemu-3.1.0-rc0/tcg/tcg.c:3598
> #5 0x000000006003ef9a in tb_gen_code (cpu=cpu@entry=0x627e0010, pc=pc@entry=134512724, cs_base=cs_base@entry=0, flags=flags@entry=4194483, cflags=cflags@entry=0)
> at /home/alberto/Documents/qemu-3.1.0-rc0/accel/tcg/translate-all.c:1752
> #6 0x000000006003d979 in tb_find (cf_mask=0, tb_exit=0, last_tb=0x0, cpu=0x0) at /home/alberto/Documents/qemu-3.1.0-rc0/accel/tcg/cpu-exec.c:404
> #7 cpu_exec (cpu=cpu@entry=0x627e0010) at /home/alberto/Documents/qemu-3.1.0-rc0/accel/tcg/cpu-exec.c:724
> #8 0x000000006006e1a0 in cpu_loop (env=env@entry=0x627e82c0) at /home/alberto/Documents/qemu-3.1.0-rc0/linux-user/i386/cpu_loop.c:93
> #9 0x00000000600037c5 in main (argc=2, argv=0x7fffffffdd28, envp=<optimized out>) at /home/alberto/Documents/qemu-3.1.0-rc0/linux-user/main.c:819
> (gdb)
>
> Testcase:
> ---------
>
> Find ELF file attached.
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/qemu/+bug/1803160/+subscriptions
>

[Alberto Ortega (aortega)]

I've just opened #1807675 for the new bug.

Thanks!