Re: [PATCH net-next v3 0/4] vsock: Add flags field in the vsock address

[Paraschiv, Andra-Irina]

On 14/12/2020 10:13, Stefano Garzarella wrote:
> On Sat, Dec 12, 2020 at 09:16:08AM -0800, Jakub Kicinski wrote:
> > On Fri, 11 Dec 2020 16:24:13 +0100 Stefano Garzarella wrote:
> > > On Fri, Dec 11, 2020 at 12:32:37PM +0200, Andra Paraschiv wrote:
> > > >vsock enables communication between virtual machines and the host 
> > > they are
> > > >running on. Nested VMs can be setup to use vsock channels, as the 
> > > multi
> > > >transport support has been available in the mainline since the v5.5 
> > > Linux kernel
> > > >has been released.
> > > >
> > > >Implicitly, if no host->guest vsock transport is loaded, all the 
> > > vsock packets
> > > >are forwarded to the host. This behavior can be used to setup 
> > > communication
> > > >channels between sibling VMs that are running on the same host. One 
> > > example can
> > > >be the vsock channels that can be established within AWS Nitro 
> > > Enclaves
> > > >(see Documentation/virt/ne_overview.rst).
> > > >
> > > >To be able to explicitly mark a connection as being used for a 
> > > certain use case,
> > > >add a flags field in the vsock address data structure. The value of 
> > > the flags
> > > >field is taken into consideration when the vsock transport is 
> > > assigned. This way
> > > >can distinguish between different use cases, such as nested VMs / 
> > > local
> > > >communication and sibling VMs.
> > > >
> > > >The flags field can be set in the user space application connect 
> > > logic. On the
> > > >listen path, the field can be set in the kernel space logic.
> > > >
> > >
> > > I reviewed all the patches and they are in a good shape!
> > >
> > > Maybe the last thing to add is a flags check in the
> > > vsock_addr_validate(), to avoid that flags that we don't know how to
> > > handle are specified.
> > > For example if in the future we add new flags that this version of the
> > > kernel is not able to satisfy, we should return an error to the
> > > application.
> > >
> > > I mean something like this:
> > >
> > >      diff --git a/net/vmw_vsock/vsock_addr.c 
> > > b/net/vmw_vsock/vsock_addr.c
> > >      index 909de26cb0e7..73bb1d2fa526 100644
> > >      --- a/net/vmw_vsock/vsock_addr.c
> > >      +++ b/net/vmw_vsock/vsock_addr.c
> > >      @@ -22,6 +22,8 @@ EXPORT_SYMBOL_GPL(vsock_addr_init);
> > >
> > >       int vsock_addr_validate(const struct sockaddr_vm *addr)
> > >       {
> > >      +       unsigned short svm_valid_flags = VMADDR_FLAG_TO_HOST;
> > >      +
> > >              if (!addr)
> > >                      return -EFAULT;
> > >
> > >      @@ -31,6 +33,9 @@ int vsock_addr_validate(const struct 
> > > sockaddr_vm *addr)
> > >              if (addr->svm_zero[0] != 0)
> > >                      return -EINVAL;
> >
> > Strictly speaking this check should be superseded by the check below
> > (AKA removed). We used to check svm_zero[0], with the new field added
> > this now checks svm_zero[2]. Old applications may have not initialized
> > svm_zero[2] (we're talking about binary compatibility here, apps built
> > with old headers).
> >
> > >      +       if (addr->svm_flags & ~svm_valid_flags)
> > >      +               return -EINVAL;
> >
> > The flags should also probably be one byte (we can define a "more
> > flags" flag to unlock further bytes) - otherwise on big endian the
> > new flag will fall into svm_zero[1] so the v3 improvements are moot
> > for big endian, right?
>
> Right, I assumed the entire svm_zero[] was zeroed out, but we can't be
> sure.
>
> So, I agree to change the svm_flags to 1 byte (__u8), and remove the
> superseded check that you pointed out.
> With these changes we should be fully binary compatibility.

Here we go, sent out v4:

https://lore.kernel.org/lkml/20201214161122.37717-1-andraprs@xxxxxxxxxx/

Thank you both.

Andra

> > >              return 0;
> > >       }
> > >       EXPORT_SYMBOL_GPL(vsock_addr_validate);




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