Re: [Qemu-devel] [PATCH for-3.1] nvme: fix out-of-bounds access to the CMB

[Paolo Bonzini]

On 19/11/18 16:23, Mark Kanda wrote:
> For CVE-2018-16847, I just noticed Kevin pulled in Li's previous fix (as
> opposed to this one). Was this done in error?

Probably.  Kevin, can you revert and apply this one instead?  I don't
care if 3.1 or 3.2, but the previous fix is pointless complication.

Paolo

> 
> Thanks,
> 
> -Mark
> 
> On 11/16/2018 3:31 AM, Paolo Bonzini wrote:
>> Because the CMB BAR has a min_access_size of 2, if you read the last
>> byte it will try to memcpy *2* bytes from n->cmbuf, causing an off-by-one
>> error.  This is CVE-2018-16847.
>>
>> Another way to fix this might be to register the CMB as a RAM memory
>> region, which would also be more efficient.  However, that might be a
>> change for big-endian machines; I didn't think this through and I don't
>> know how real hardware works.  Add a basic testcase for the CMB in case
>> somebody does this change later on.
>>
>> Cc: Keith Busch <address@hidden>
>> Cc: address@hidden
>> Cc: Li Qiang <address@hidden>
>> Signed-off-by: Paolo Bonzini <address@hidden>
>> ---
>>   hw/block/nvme.c        |  2 +-
>>   tests/Makefile.include |  2 +-
>>   tests/nvme-test.c      | 58 +++++++++++++++++++++++++++++++++++++++---
>>   3 files changed, 57 insertions(+), 5 deletions(-)
>>
>> diff --git a/hw/block/nvme.c b/hw/block/nvme.c
>> index 09d7c90259..5d92794ef7 100644
>> --- a/hw/block/nvme.c
>> +++ b/hw/block/nvme.c
>> @@ -1192,7 +1192,7 @@ static const MemoryRegionOps nvme_cmb_ops = {
>>       .write = nvme_cmb_write,
>>       .endianness = DEVICE_LITTLE_ENDIAN,
>>       .impl = {
>> -        .min_access_size = 2,
>> +        .min_access_size = 1,
>>           .max_access_size = 8,
>>       },
>>   };
>> diff --git a/tests/Makefile.include b/tests/Makefile.include
>> index 613242bc6e..fb0b449c02 100644
>> --- a/tests/Makefile.include
>> +++ b/tests/Makefile.include
>> @@ -730,7 +730,7 @@ tests/test-hmp$(EXESUF): tests/test-hmp.o
>>   tests/machine-none-test$(EXESUF): tests/machine-none-test.o
>>   tests/drive_del-test$(EXESUF): tests/drive_del-test.o
>> $(libqos-virtio-obj-y)
>>   tests/qdev-monitor-test$(EXESUF): tests/qdev-monitor-test.o
>> $(libqos-pc-obj-y)
>> -tests/nvme-test$(EXESUF): tests/nvme-test.o
>> +tests/nvme-test$(EXESUF): tests/nvme-test.o $(libqos-pc-obj-y)
>>   tests/pvpanic-test$(EXESUF): tests/pvpanic-test.o
>>   tests/i82801b11-test$(EXESUF): tests/i82801b11-test.o
>>   tests/ac97-test$(EXESUF): tests/ac97-test.o
>> diff --git a/tests/nvme-test.c b/tests/nvme-test.c
>> index 7674a446e4..2abb3b6d19 100644
>> --- a/tests/nvme-test.c
>> +++ b/tests/nvme-test.c
>> @@ -8,11 +8,64 @@
>>    */
>>     #include "qemu/osdep.h"
>> +#include "qemu/units.h"
>>   #include "libqtest.h"
>> +#include "libqos/libqos-pc.h"
>> +
>> +static QOSState *qnvme_start(const char *extra_opts)
>> +{
>> +    QOSState *qs;
>> +    const char *arch = qtest_get_arch();
>> +    const char *cmd = "-drive
>> id=drv0,if=none,file=null-co://,format=raw "
>> +                      "-device nvme,addr=0x4.0,serial=foo,drive=drv0
>> %s";
>> +
>> +    if (strcmp(arch, "i386") == 0 || strcmp(arch, "x86_64") == 0) {
>> +        qs = qtest_pc_boot(cmd, extra_opts ? : "");
>> +        global_qtest = qs->qts;
>> +        return qs;
>> +    }
>> +
>> +    g_printerr("nvme tests are only available on x86\n");
>> +    exit(EXIT_FAILURE);
>> +}
>> +
>> +static void qnvme_stop(QOSState *qs)
>> +{
>> +    qtest_shutdown(qs);
>> +}
>>   -/* Tests only initialization so far. TODO: Replace with functional
>> tests */
>>   static void nop(void)
>>   {
>> +    QOSState *qs;
>> +
>> +    qs = qnvme_start(NULL);
>> +    qnvme_stop(qs);
>> +}
>> +
>> +static void nvmetest_cmb_test(void)
>> +{
>> +    const int cmb_bar_size = 2 * MiB;
>> +    QOSState *qs;
>> +    QPCIDevice *pdev;
>> +    QPCIBar bar;
>> +
>> +    qs = qnvme_start("-global nvme.cmb_size_mb=2");
>> +    pdev = qpci_device_find(qs->pcibus, QPCI_DEVFN(4,0));
>> +    g_assert(pdev != NULL);
>> +
>> +    qpci_device_enable(pdev);
>> +    bar = qpci_iomap(pdev, 2, NULL);
>> +
>> +    qpci_io_writel(pdev, bar, 0, 0xccbbaa99);
>> +    g_assert_cmpint(qpci_io_readb(pdev, bar, 0), ==, 0x99);
>> +    g_assert_cmpint(qpci_io_readw(pdev, bar, 0), ==, 0xaa99);
>> +
>> +    /* Test partially out-of-bounds accesses.  */
>> +    qpci_io_writel(pdev, bar, cmb_bar_size - 1, 0x44332211);
>> +    g_assert_cmpint(qpci_io_readb(pdev, bar, cmb_bar_size - 1), ==,
>> 0x11);
>> +    g_assert_cmpint(qpci_io_readw(pdev, bar, cmb_bar_size - 1), !=,
>> 0x2211);
>> +    g_assert_cmpint(qpci_io_readl(pdev, bar, cmb_bar_size - 1), !=,
>> 0x44332211);
>> +    qnvme_stop(qs);
>>   }
>>     int main(int argc, char **argv)
>> @@ -21,9 +74,8 @@ int main(int argc, char **argv)
>>         g_test_init(&argc, &argv, NULL);
>>       qtest_add_func("/nvme/nop", nop);
>> +    qtest_add_func("/nvme/cmb_test", nvmetest_cmb_test);
>>   -    qtest_start("-drive id=drv0,if=none,file=null-co://,format=raw "
>> -                "-device nvme,drive=drv0,serial=foo");
>>       ret = g_test_run();
>>         qtest_end();
>>