[Bug 218339] kernel goes unresponsive if single-stepping over an instruction which writes to an address for which a hardware read/write watchpoint has been set

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=218339

--- Comment #4 from Anthony L. Eden (anthony.louis.eden@gmail.com) ---
>> I tried on my side but can't reproducce it, logs below. Any steps I missed ?

Nope, it looks like you did everything right.



I spent a little more time investigating this, since for me it's trivial to
reproduce. I was able to get the guest kernel vmlinux *with* debugging
information from the linux-image-6.1.0-15-amd64-dbg debian package.

After entering the final `stepi` within gdb, which is when the guest goes
totally unresponsive, in htop I see qemu-system-x86_64 is taking up 100% CPU.
Like I said, the thread call stacks in the qemu process look typical.

I used the qemu monitor command 'dump-guest-memory -p /root/linux.core' three
separate times after the guest went unresponsive, and all three of the core
file backtraces look like this:

#0  pv_native_set_debugreg (regno=7, val=0) at
arch/x86/include/asm/debugreg.h:92
#1  0xffffffff81a21533 in set_debugreg (reg=7, val=0) at
arch/x86/include/asm/paravirt.h:129
#2  local_db_save () at arch/x86/include/asm/debugreg.h:127
#3  exc_debug_kernel (dr6=0, regs=0xfffffe0000010f58) at
arch/x86/kernel/traps.c:1038
#4  exc_debug (regs=0xfffffe0000010f58) at arch/x86/kernel/traps.c:1175
#5  0xffffffff81c00c6a in asm_exc_debug () at
/build/reproducible-path/linux-6.1.66/arch/x86/include/asm/idtentry.h:606
#6  0x0000000000000000 in ?? ()



My VM was in a self-contained folder with its own run script on the host so I
made a tarball of it. It is available for download here (~9 GB):

https://drive.google.com/file/d/1r3tlrw8kG17vFwXzP6ETv76ptNhbLYjt/view?usp=sharing

Usage:

$ tar xvSf deb-vm-x86_64.tar
$ cd deb-vm-x86_64/
$ ./run.sh

In another terminal,

$ screen /dev/pts/23 115200
$ login as user 'root' with password 'root'

Once inside,

$ gdb /usr/bin/ls
$ starti
...


Oh and by the way, the version of qemu-system-x86_64 on my host is 7.2.7
(Debian 1:7.2+dfsg-7+deb12u3).

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.