Re: [Qemu-devel] [PATCH 2/2] pci-assign: Fix memory out of bound when MSI-X table not fit in a single page

[Gonglei (Arei)]

Hi,

> > QEMU only mmap MSIX_PAGE_SIZE memory for all pci devices in
> > assigned_dev_register_msix_mmio(), meanwhile the set the one
> > page memmory to zero, so the rest memory will be random value
> > (maybe etnry.data is not 0). In the assigned_dev_update_msix_mmio()
> > maybe occur the issue of entry_nr > 256, and the kmod reports
> > the EINVAL error.
> >
> > Signed-off-by: Gonglei <address@hidden>
> 
> Okay so this kind of works because guest does not try
> to use so many vectors.
> 
Yes. It's true.

> But I think it's better not to give guest more entries
> than we can actually support.
> 
> How about tweaking MSIX capability exposed to guest to limit table size?
> 
IMHO, the MSIX table entry size got form the physic NIC hardware. The software
layer shouldn't tweak the capability of real hardware, neither QEMU nor KVM. 


Best regards,
-Gonglei

> > ---
> >  hw/i386/kvm/pci-assign.c | 15 ++++++++++++---
> >  1 file changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/hw/i386/kvm/pci-assign.c b/hw/i386/kvm/pci-assign.c
> > index 570333f..d25a19e 100644
> > --- a/hw/i386/kvm/pci-assign.c
> > +++ b/hw/i386/kvm/pci-assign.c
> > @@ -37,6 +37,7 @@
> >  #include "hw/pci/pci.h"
> >  #include "hw/pci/msi.h"
> >  #include "kvm_i386.h"
> > +#include "qemu/osdep.h"
> >
> >  #define MSIX_PAGE_SIZE 0x1000
> >
> > @@ -59,6 +60,9 @@
> >  #define DEBUG(fmt, ...)
> >  #endif
> >
> > +/* the msix-table size readed from pci device config */
> > +static int msix_table_size;
> > +
> >  typedef struct PCIRegion {
> >      int type;           /* Memory or port I/O */
> >      int valid;
> > @@ -1604,7 +1608,12 @@ static void
> assigned_dev_msix_reset(AssignedDevice *dev)
> >
> >  static int assigned_dev_register_msix_mmio(AssignedDevice *dev)
> >  {
> > -    dev->msix_table = mmap(NULL, MSIX_PAGE_SIZE,
> PROT_READ|PROT_WRITE,
> > +    msix_table_size = ROUND_UP(dev->msix_max * sizeof(struct
> MSIXTableEntry),
> > +                                MSIX_PAGE_SIZE);
> > +
> > +    DEBUG("msix_table_size: 0x%x\n", msix_table_size);
> > +
> > +    dev->msix_table = mmap(NULL, msix_table_size,
> PROT_READ|PROT_WRITE,
> >                             MAP_ANONYMOUS|MAP_PRIVATE, 0, 0);
> >      if (dev->msix_table == MAP_FAILED) {
> >          error_report("fail allocate msix_table! %s", strerror(errno));
> > @@ -1615,7 +1624,7 @@ static int
> assigned_dev_register_msix_mmio(AssignedDevice *dev)
> >      assigned_dev_msix_reset(dev);
> >
> >      memory_region_init_io(&dev->mmio, OBJECT(dev),
> &assigned_dev_msix_mmio_ops,
> > -                          dev, "assigned-dev-msix",
> MSIX_PAGE_SIZE);
> > +                          dev, "assigned-dev-msix", msix_table_size);
> >      return 0;
> >  }
> >
> > @@ -1627,7 +1636,7 @@ static void
> assigned_dev_unregister_msix_mmio(AssignedDevice *dev)
> >
> >      memory_region_destroy(&dev->mmio);
> >
> > -    if (munmap(dev->msix_table, MSIX_PAGE_SIZE) == -1) {
> > +    if (munmap(dev->msix_table, msix_table_size) == -1) {
> >          error_report("error unmapping msix_table! %s", strerror(errno));
> >      }
> >      dev->msix_table = NULL;
> > --
> > 1.7.12.4
> >
> >