large -initrd can wrap around in memory causing memory corruption

Bug #1186984 reported by Richard Jones on 2013-06-03
12
This bug affects 2 people
Affects Status Importance Assigned to Milestone
QEMU
Undecided
Unassigned

Bug Description

We don't use large -initrd in libguestfs any more, but I noticed that a large -initrd file now crashes qemu spectacularly:

$ ls -lh /tmp/kernel /tmp/initrd
-rw-r--r--. 1 rjones rjones 273M Jun 3 14:02 /tmp/initrd
lrwxrwxrwx. 1 rjones rjones 35 Jun 3 14:02 /tmp/kernel -> /boot/vmlinuz-3.9.4-200.fc18.x86_64

$ ./x86_64-softmmu/qemu-system-x86_64 -L pc-bios \
    -kernel /tmp/kernel -initrd /tmp/initrd -hda /tmp/test1.img -serial stdio \
    -append console=ttyS0

qemu crashes with one of several errors:

PFLASH: Possible BUG - Write block confirm

qemu: fatal: Trying to execute code outside RAM or ROM at 0x00000000000b96cd

If -enable-kvm is used:

KVM: injection failed, MSI lost (Operation not permitted)

In all cases the SDL display fills up with coloured blocks before the crash (see the attached screenshot).

Richard Jones (rjones-redhat) wrote :
Richard Jones (rjones-redhat) wrote :

I'm using qemu from git (f10acc8b38d65a66ffa0588a036489d7fa6a593e).

Richard Jones (rjones-redhat) wrote :

One way to reproduce this is to just use a large (200 MB) completely random initrd. Note this error seems to happen a long time before even the kernel starts up, so the actual content of the initrd doesn't matter.

dd if=/dev/urandom of=/tmp/initrd bs=1M count=200
qemu-system-x86_64 -kernel /boot/vmlinuz -initrd /tmp/initrd -serial stdio -append console=ttyS0

Richard Jones (rjones-redhat) wrote :

OK I see what's happening. Because I forgot about the -m option, qemu allocates 128 MB of RAM. It's obviously wrapping around in memory and overwriting all the low memory.

If you add (eg) -m 1024 it works.

summary: - large -initrd crashes qemu
+ large -initrd can wrap around in memory causing memory corruption

Just saw something similar with qemu 2.2.1:

KVM: injection failed, MSI lost (Input/output error)
qemu-system-x86_64: /home/bart/software/qemu-2.2.1/hw/net/vhost_net.c:264: vhost_net_stop_one: Assertion `r >= 0' failed.
2015-03-23 02:44:44.952+0000: shutting down

Richard Jones (rjones-redhat) wrote :

Although the error message is the same, the bug in comment 5 seems completely different. Please open a new bug about this issue, giving *all* details - including the full qemu command line.

Thanks Richard for the quick feedback. A new bug report has been created as https://bugs.launchpad.net/qemu/+bug/1435359.

Thomas Huth (th-huth) wrote :

Triaging old bug tickets... can you still reproduce this issue with the latest version of QEMU? Or could we close this ticket nowadays?

Changed in qemu:
status: New → Incomplete
Richard Jones (rjones-redhat) wrote :

The answer is I don't know. Closing this bug seems correct unless someone can reproduce the original problem.

Launchpad Janitor (janitor) wrote :

[Expired for QEMU because there has been no activity for 60 days.]

Changed in qemu:
status: Incomplete → Expired
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