KVM: x86/xen: fix 32-bit pointer cast

[PATCH] KVM: x86/xen: fix 32-bit pointer cast

Posted by Arnd Bergmann 1 year, 11 months ago

From: Arnd Bergmann <arnd@arndb.de>

shared_info.hva is a 64-bit variable, so casting to a pointer causes
a warning in 32-bit builds:

arch/x86/kvm/xen.c: In function 'kvm_xen_hvm_set_attr':
arch/x86/kvm/xen.c:660:45: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
  660 |                         void __user * hva = (void *)data->u.shared_info.hva;

Replace the cast with a u64_to_user_ptr() call that does the right thing.

Fixes: 01a871852b11 ("KVM: x86/xen: allow shared_info to be mapped by fixed HVA")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/x86/kvm/xen.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 01c0fd138d2f..8a04e0ae9245 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -657,7 +657,7 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 						     gfn_to_gpa(gfn), PAGE_SIZE);
 			}
 		} else {
-			void __user * hva = (void *)data->u.shared_info.hva;
+			void __user * hva = u64_to_user_ptr(data->u.shared_info.hva);
 
 			if (!PAGE_ALIGNED(hva) || !access_ok(hva, PAGE_SIZE)) {
 				r = -EINVAL;
-- 
2.39.2

Re: [PATCH] KVM: x86/xen: fix 32-bit pointer cast

Posted by Paul Durrant 1 year, 11 months ago

On 22/02/2024 10:03, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> shared_info.hva is a 64-bit variable, so casting to a pointer causes
> a warning in 32-bit builds:
> 
> arch/x86/kvm/xen.c: In function 'kvm_xen_hvm_set_attr':
> arch/x86/kvm/xen.c:660:45: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>    660 |                         void __user * hva = (void *)data->u.shared_info.hva;
> 
> Replace the cast with a u64_to_user_ptr() call that does the right thing.

Thanks Arnd. I'd just got a ping from kernel test robot for lack of 
__user qualifier in the cast 
(https://lore.kernel.org/oe-kbuild-all/202402221721.mhF8MNVh-lkp@intel.com/), 
which this should also fix.

> 
> Fixes: 01a871852b11 ("KVM: x86/xen: allow shared_info to be mapped by fixed HVA")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>   arch/x86/kvm/xen.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 

Reviewed-by: Paul Durrant <paul@xen.org>

> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
> index 01c0fd138d2f..8a04e0ae9245 100644
> --- a/arch/x86/kvm/xen.c
> +++ b/arch/x86/kvm/xen.c
> @@ -657,7 +657,7 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
>   						     gfn_to_gpa(gfn), PAGE_SIZE);
>   			}
>   		} else {
> -			void __user * hva = (void *)data->u.shared_info.hva;
> +			void __user * hva = u64_to_user_ptr(data->u.shared_info.hva);
>   
>   			if (!PAGE_ALIGNED(hva) || !access_ok(hva, PAGE_SIZE)) {
>   				r = -EINVAL;

Re: [PATCH] KVM: x86/xen: fix 32-bit pointer cast

Posted by Sean Christopherson 1 year, 11 months ago

On Thu, Feb 22, 2024, Paul Durrant wrote:
> On 22/02/2024 10:03, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@arndb.de>
> > 
> > shared_info.hva is a 64-bit variable, so casting to a pointer causes
> > a warning in 32-bit builds:
> > 
> > arch/x86/kvm/xen.c: In function 'kvm_xen_hvm_set_attr':
> > arch/x86/kvm/xen.c:660:45: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
> >    660 |                         void __user * hva = (void *)data->u.shared_info.hva;
> > 
> > Replace the cast with a u64_to_user_ptr() call that does the right thing.
> 
> Thanks Arnd. I'd just got a ping from kernel test robot for lack of __user
> qualifier in the cast
> (https://lore.kernel.org/oe-kbuild-all/202402221721.mhF8MNVh-lkp@intel.com/),
> which this should also fix.

Ya, 'tis a good bot.  I squashed this in.   Paul/David, new hashes for the
affected commits are below.

Thanks Arnd!

  KVM: x86/xen: allow shared_info to be mapped by fixed HVA
  https://github.com/kvm-x86/linux/commit/b9220d32799a
  KVM: x86/xen: allow vcpu_info to be mapped by fixed HVA
  https://github.com/kvm-x86/linux/commit/3991f35805d0
  KVM: selftests: map Xen's shared_info page using HVA rather than GFN
  https://github.com/kvm-x86/linux/commit/9397b5334af1
  KVM: selftests: re-map Xen's vcpu_info using HVA rather than GPA
  https://github.com/kvm-x86/linux/commit/b4dfbfdc9538
  KVM: x86/xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA capability
  https://github.com/kvm-x86/linux/commit/615451d8cb3f
  KVM: pfncache: check the need for invalidation under read lock first
  https://github.com/kvm-x86/linux/commit/9fa336e343b2
  KVM: x86/xen: allow vcpu_info content to be 'safely' copied
  https://github.com/kvm-x86/linux/commit/003d914220c9