[v1] amd_iommu: Return error on machines with no PCI

[Qemu-devel] [PATCH] amd_iommu: Return error on machines with no PCI

Posted by Mohammed Gamal 6 years, 7 months ago

Starting the following command line causes a segfault
qemu-system-x86_64 -S -machine isapc,accel=kvm -device amd-iommu

This is due to the fact that the machine type 'isapc' doesn't have
a PCI bus, while amd_iommu doesn't check if the machine has PCI support
and subsequently does a null-pointer access. AMD IOMMU shouldn't even work
if the target machine doesn't have PCI.

Add a check for PCI on the given machine type and return an error if PCI
is not supported.

Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
---
 hw/i386/amd_iommu.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
index 334938a..9a667b7 100644
--- a/hw/i386/amd_iommu.c
+++ b/hw/i386/amd_iommu.c
@@ -1153,6 +1153,13 @@ static void amdvi_realize(DeviceState *dev, Error **err)
     }
 
     bus = pcms->bus;
+
+    if (!bus) {
+        error_setg(err, "Machine-type '%s' does not support PCI",
+                   mc->name);
+        return;
+    }
+
     s->iotlb = g_hash_table_new_full(amdvi_uint64_hash,
                                      amdvi_uint64_equal, g_free, g_free);
 
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH] amd_iommu: Return error on machines with no PCI

Posted by Thomas Huth 6 years, 7 months ago

On 14.09.2017 22:18, Mohammed Gamal wrote:
> Starting the following command line causes a segfault
> qemu-system-x86_64 -S -machine isapc,accel=kvm -device amd-iommu
> 
> This is due to the fact that the machine type 'isapc' doesn't have
> a PCI bus, while amd_iommu doesn't check if the machine has PCI support
> and subsequently does a null-pointer access. AMD IOMMU shouldn't even work
> if the target machine doesn't have PCI.
> 
> Add a check for PCI on the given machine type and return an error if PCI
> is not supported.
> 
> Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
> ---
>  hw/i386/amd_iommu.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
> index 334938a..9a667b7 100644
> --- a/hw/i386/amd_iommu.c
> +++ b/hw/i386/amd_iommu.c
> @@ -1153,6 +1153,13 @@ static void amdvi_realize(DeviceState *dev, Error **err)
>      }
>  
>      bus = pcms->bus;
> +
> +    if (!bus) {
> +        error_setg(err, "Machine-type '%s' does not support PCI",
> +                   mc->name);
> +        return;
> +    }
> +
>      s->iotlb = g_hash_table_new_full(amdvi_uint64_hash,
>                                       amdvi_uint64_equal, g_free, g_free);
>  
> 

Patch looks fine to me, but I think it would also be sufficient to
change the check at the beginning of the function to test "if (!pcms ||
!pcms->bus)" instead of just "if (!pcms)" ... the error message
"Machine-type 'xxx' not supported by amd-iommu" is also adequate if
there is no PCI bus available on the system.

 Thomas

Re: [Qemu-devel] [PATCH] amd_iommu: Return error on machines with no PCI

Posted by Eduardo Habkost 6 years, 7 months ago

On Thu, Sep 14, 2017 at 10:24:23PM +0200, Thomas Huth wrote:
> On 14.09.2017 22:18, Mohammed Gamal wrote:
> > Starting the following command line causes a segfault
> > qemu-system-x86_64 -S -machine isapc,accel=kvm -device amd-iommu
> > 
> > This is due to the fact that the machine type 'isapc' doesn't have
> > a PCI bus, while amd_iommu doesn't check if the machine has PCI support
> > and subsequently does a null-pointer access. AMD IOMMU shouldn't even work
> > if the target machine doesn't have PCI.
> > 
> > Add a check for PCI on the given machine type and return an error if PCI
> > is not supported.
> > 
> > Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
> > ---
> >  hw/i386/amd_iommu.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
> > index 334938a..9a667b7 100644
> > --- a/hw/i386/amd_iommu.c
> > +++ b/hw/i386/amd_iommu.c
> > @@ -1153,6 +1153,13 @@ static void amdvi_realize(DeviceState *dev, Error **err)
> >      }
> >  
> >      bus = pcms->bus;
> > +
> > +    if (!bus) {
> > +        error_setg(err, "Machine-type '%s' does not support PCI",
> > +                   mc->name);
> > +        return;
> > +    }
> > +
> >      s->iotlb = g_hash_table_new_full(amdvi_uint64_hash,
> >                                       amdvi_uint64_equal, g_free, g_free);
> >  
> > 
> 
> Patch looks fine to me, but I think it would also be sufficient to
> change the check at the beginning of the function to test "if (!pcms ||
> !pcms->bus)" instead of just "if (!pcms)" ... the error message
> "Machine-type 'xxx' not supported by amd-iommu" is also adequate if
> there is no PCI bus available on the system.

I agree this would be much simpler.

-- 
Eduardo

Re: [Qemu-devel] [PATCH] amd_iommu: Return error on machines with no PCI

Posted by Peter Xu 6 years, 7 months ago

On Thu, Sep 14, 2017 at 05:31:38PM -0300, Eduardo Habkost wrote:
> On Thu, Sep 14, 2017 at 10:24:23PM +0200, Thomas Huth wrote:
> > On 14.09.2017 22:18, Mohammed Gamal wrote:
> > > Starting the following command line causes a segfault
> > > qemu-system-x86_64 -S -machine isapc,accel=kvm -device amd-iommu
> > > 
> > > This is due to the fact that the machine type 'isapc' doesn't have
> > > a PCI bus, while amd_iommu doesn't check if the machine has PCI support
> > > and subsequently does a null-pointer access. AMD IOMMU shouldn't even work
> > > if the target machine doesn't have PCI.
> > > 
> > > Add a check for PCI on the given machine type and return an error if PCI
> > > is not supported.
> > > 
> > > Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
> > > ---
> > >  hw/i386/amd_iommu.c | 7 +++++++
> > >  1 file changed, 7 insertions(+)
> > > 
> > > diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
> > > index 334938a..9a667b7 100644
> > > --- a/hw/i386/amd_iommu.c
> > > +++ b/hw/i386/amd_iommu.c
> > > @@ -1153,6 +1153,13 @@ static void amdvi_realize(DeviceState *dev, Error **err)
> > >      }
> > >  
> > >      bus = pcms->bus;
> > > +
> > > +    if (!bus) {
> > > +        error_setg(err, "Machine-type '%s' does not support PCI",
> > > +                   mc->name);
> > > +        return;
> > > +    }
> > > +
> > >      s->iotlb = g_hash_table_new_full(amdvi_uint64_hash,
> > >                                       amdvi_uint64_equal, g_free, g_free);
> > >  
> > > 
> > 
> > Patch looks fine to me, but I think it would also be sufficient to
> > change the check at the beginning of the function to test "if (!pcms ||
> > !pcms->bus)" instead of just "if (!pcms)" ... the error message
> > "Machine-type 'xxx' not supported by amd-iommu" is also adequate if
> > there is no PCI bus available on the system.
> 
> I agree this would be much simpler.

Even, shall we move the pcms && bus check into x86_iommu_realize()
directly?  Then we will only need one single patch for Intel/AMD, and
it's also a cleanup.  Thanks,

-- 
Peter Xu

Re: [Qemu-devel] [PATCH] amd_iommu: Return error on machines with no PCI

Posted by Mohammed Gamal 6 years, 7 months ago

On Fri, 2017-09-15 at 10:07 +0800, Peter Xu wrote:
> On Thu, Sep 14, 2017 at 05:31:38PM -0300, Eduardo Habkost wrote:
> > On Thu, Sep 14, 2017 at 10:24:23PM +0200, Thomas Huth wrote:
> > > On 14.09.2017 22:18, Mohammed Gamal wrote:
> > > > Starting the following command line causes a segfault
> > > > qemu-system-x86_64 -S -machine isapc,accel=kvm -device amd-iommu
> > > > 
> > > > This is due to the fact that the machine type 'isapc' doesn't have
> > > > a PCI bus, while amd_iommu doesn't check if the machine has PCI support
> > > > and subsequently does a null-pointer access. AMD IOMMU shouldn't even work
> > > > if the target machine doesn't have PCI.
> > > > 
> > > > Add a check for PCI on the given machine type and return an error if PCI
> > > > is not supported.
> > > > 
> > > > Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
> > > > ---
> > > >  hw/i386/amd_iommu.c | 7 +++++++
> > > >  1 file changed, 7 insertions(+)
> > > > 
> > > > diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
> > > > index 334938a..9a667b7 100644
> > > > --- a/hw/i386/amd_iommu.c
> > > > +++ b/hw/i386/amd_iommu.c
> > > > @@ -1153,6 +1153,13 @@ static void amdvi_realize(DeviceState *dev, Error **err)
> > > >      }
> > > >  
> > > >      bus = pcms->bus;
> > > > +
> > > > +    if (!bus) {
> > > > +        error_setg(err, "Machine-type '%s' does not support PCI",
> > > > +                   mc->name);
> > > > +        return;
> > > > +    }
> > > > +
> > > >      s->iotlb = g_hash_table_new_full(amdvi_uint64_hash,
> > > >                                       amdvi_uint64_equal, g_free, g_free);
> > > >  
> > > > 
> > > 
> > > Patch looks fine to me, but I think it would also be sufficient to
> > > change the check at the beginning of the function to test "if (!pcms ||
> > > !pcms->bus)" instead of just "if (!pcms)" ... the error message
> > > "Machine-type 'xxx' not supported by amd-iommu" is also adequate if
> > > there is no PCI bus available on the system.
> > 
> > I agree this would be much simpler.
> 
> Even, shall we move the pcms && bus check into x86_iommu_realize()
> directly?  Then we will only need one single patch for Intel/AMD, and
> it's also a cleanup.  Thanks,

Although it's more straight forward to do the checks in amdvi_realize()
and vtd_realize() at the moment, I think moving the checks to
x86_iommu_realize() would be better on the longer term. I will be
sending out a new patch with this change shortly.

Regards,
Mohammed