Re: [Qemu-devel] [PULL 00/19] Migration patches

From: "Daniel P. Berrangé" <berrange@redhat.com>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: Juan Quintela <quintela@redhat.com>,
	Laurent Vivier <lvivier@redhat.com>,
	Thomas Huth <thuth@redhat.com>, kvm-devel <kvm@vger.kernel.org>,
	QEMU Developers <qemu-devel@nongnu.org>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Richard Henderson <rth@twiddle.net>
Subject: Re: [Qemu-devel] [PULL 00/19] Migration patches
Date: Mon, 15 Jul 2019 15:04:41 +0100	[thread overview]
Message-ID: <20190715140441.GJ30298@redhat.com> (raw)
In-Reply-To: <CAFEAcA9ncjtGdc8CZOJBDBRtzEU8oL7YicVg5PtyiiO2O4z51w@mail.gmail.com>

On Mon, Jul 15, 2019 at 12:16:57PM +0100, Peter Maydell wrote:
> On Fri, 12 Jul 2019 at 17:33, Peter Maydell <peter.maydell@linaro.org> wrote:
> > Still fails on aarch32 host, I'm afraid:
> >
> > MALLOC_PERTURB_=${MALLOC_PERTURB_:-$(( ${RANDOM:-0} % 255 + 1))}
> > QTEST_QEMU_BINARY=aarch64-softmmu/qemu-system-aarch64
> > QTEST_QEMU_IMG=qemu-img tests/migration-test -m=quick -k --tap <
> > /dev/null | ./scripts/tap-driver.pl --test-name="migration-test"
> > PASS 1 migration-test /aarch64/migration/deprecated
> > PASS 2 migration-test /aarch64/migration/bad_dest
> > PASS 3 migration-test /aarch64/migration/fd_proto
> > PASS 4 migration-test /aarch64/migration/postcopy/unix
> > PASS 5 migration-test /aarch64/migration/postcopy/recovery
> > PASS 6 migration-test /aarch64/migration/precopy/unix
> > PASS 7 migration-test /aarch64/migration/precopy/tcp
> > PASS 8 migration-test /aarch64/migration/xbzrle/unix
> > malloc(): memory corruption
> > Broken pipe
> > qemu-system-aarch64: load of migration failed: Invalid argument
> > /home/peter.maydell/qemu/tests/libqtest.c:137: kill_qemu() tried to
> > terminate QEMU process but encountered exit status 1
> > Aborted
> > ERROR - too few tests run (expected 9, got 8)
> > /home/peter.maydell/qemu/tests/Makefile.include:899: recipe for target
> > 'check-qtest-aarch64' failed
> 
> A run with valgrind:
> 
> (armhf)pmaydell@mustang-maydell:~/qemu/build/all-a32$
> QTEST_QEMU_BINARY='valgrind aarch64-softmmu/qemu-system-aarch64'
> tests/migration-test -v -p '/aarch64/migration/multifd/tcp'
> /aarch64/migration/multifd/tcp: ==4034== Memcheck, a memory error detector
> ==4034== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
> ==4034== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
> ==4034== Command: aarch64-softmmu/qemu-system-aarch64 -qtest
> unix:/tmp/qtest-4033.sock -qtest-log /dev/null -chardev
> socket,path=/tmp/qtest-4033.qmp,id=char0 -mon
> chardev=char0,mode=control -machine accel=qtest -display none -machine
> virt,accel=kvm:tcg,gic-version=max -name vmsource,debug-threads=on
> -cpu max -m 150M -serial file:/tmp/migration-test-mSLr4A/src_serial
> -kernel /tmp/migration-test-mSLr4A/bootsect
> ==4034==
> ==4040== Memcheck, a memory error detector
> ==4040== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
> ==4040== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
> ==4040== Command: aarch64-softmmu/qemu-system-aarch64 -qtest
> unix:/tmp/qtest-4033.sock -qtest-log /dev/null -chardev
> socket,path=/tmp/qtest-4033.qmp,id=char0 -mon
> chardev=char0,mode=control -machine accel=qtest -display none -machine
> virt,accel=kvm:tcg,gic-version=max -name vmdest,debug-threads=on -cpu
> max -m 150M -serial file:/tmp/migration-test-mSLr4A/dest_serial
> -kernel /tmp/migration-test-mSLr4A/bootsect -incoming tcp:127.0.0.1:0
> ==4040==
> ==4034== Thread 5 multifdsend_0:
> ==4034== Syscall param sendmsg(msg.msg_iov[0]) points to uninitialised byte(s)
> ==4034==    at 0x5299F06: __libc_do_syscall (libc-do-syscall.S:47)
> ==4034==    by 0x5298FCB: sendmsg (sendmsg.c:28)
> ==4034==    by 0x60135D: qio_channel_socket_writev (channel-socket.c:544)
> ==4034==    by 0x5FF995: qio_channel_writev (channel.c:207)
> ==4034==    by 0x5FF995: qio_channel_writev_all (channel.c:171)
> ==4034==    by 0x5FFA0F: qio_channel_write_all (channel.c:257)
> ==4034==    by 0x26BA73: multifd_send_initial_packet (ram.c:711)
> ==4034==    by 0x26BA73: multifd_send_thread (ram.c:1085)
> ==4034==    by 0x63C0B1: qemu_thread_start (qemu-thread-posix.c:502)
> ==4034==    by 0x5290613: start_thread (pthread_create.c:463)
> ==4034==    by 0x53487FB: ??? (clone.S:73)
> ==4034==  Address 0x2320048d is on thread 5's stack
> ==4034==  in frame #5, created by multifd_send_thread (ram.c:1077)

This is a simple missing initialization

multifd_send_initial_packet has a local variable:

    MultiFDInit_t msg;

the code initializes 4 fields, but does *not* initialize the 2
padding fields, so we're writing random data. Harmless as the
receiving end will ignore padding too, but we should fill with
zeros really. so

    MultiFDInit_t msg = {0};

should fix it.

> ==4034==
> ==4034== Thread 6 multifdsend_1:
> ==4034== Invalid write of size 4
> ==4034==    at 0x26BB7C: multifd_send_fill_packet (ram.c:806)
> ==4034==    by 0x26BB7C: multifd_send_thread (ram.c:1101)
> ==4034==    by 0x63C0B1: qemu_thread_start (qemu-thread-posix.c:502)
> ==4034==    by 0x5290613: start_thread (pthread_create.c:463)
> ==4034==    by 0x53487FB: ??? (clone.S:73)
> ==4034==  Address 0x224ed668 is 0 bytes after a block of size 832 alloc'd
> ==4034==    at 0x4841BC4: calloc (vg_replace_malloc.c:711)
> ==4034==    by 0x5018269: g_malloc0 (in
> /usr/lib/arm-linux-gnueabihf/libglib-2.0.so.0.5600.4)

multifd_send_fill_packet is getting the oob write in:

    for (i = 0; i < p->pages->used; i++) {
        packet->offset[i] = cpu_to_be64(p->pages->offset[i]);
    }

offset is a variable length struct field at the end of MultiFDPacket_t:

  typedef struct {
     ...snip...
    char ramblock[256];
    uint64_t offset[];
  } __attribute__((packed)) MultiFDPacket_t;

but the packet data is allocated back in multifd_save_setup using:

        p->packet_len = sizeof(MultiFDPacket_t)
                      + sizeof(ram_addr_t) * page_count;
        p->packet = g_malloc0(p->packet_len);

Notice the field in the struct is "uint64_t" but the length we're
allocating is "ram_addr_t".

Since this is a 32-bit build, I'm guessing ram_addr_t is a 32-bit
integer and thus we're under-allocating the variable length offset
field by half

Regards,
Daniel
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