Re: [PATCH] KVM: VMX: Ensure unused kvm_tdx_capabilities fields are zeroed out

["Edgecombe, Rick P" <rick.p.edgecombe@intel.com>]

On Mon, 2025-07-14 at 15:19 -0700, Sean Christopherson wrote:
> Zero-allocate the kernel's kvm_tdx_capabilities structure and copy only
> the number of CPUID entries from the userspace structure.  As is, KVM
> doesn't ensure kernel_tdvmcallinfo_1_{r11,r12} and user_tdvmcallinfo_1_r12
> are zeroed, i.e. KVM will reflect whatever happens to be in the userspace
> structure back at usersepace, and thus may report garbage to userspace.
                         ^typo

> 
> Zeroing the entire kernel structure also provides better semantics for the
> reserved field.  E.g. if KVM extends kvm_tdx_capabilities to enumerate new
> information by repurposing bytes from the reserved field, userspace would
> be required to zero the new field in order to get useful information back
> (because older KVMs without support for the repurposed field would report
> garbage, a la the aforementioned tdvmcallinfo bugs).
> 
> Fixes: 61bb28279623 ("KVM: TDX: Get system-wide info about TDX module on initialization")
> Suggested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Reported-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Closes: https://lore.kernel.org/all/3ef581f1-1ff1-4b99-b216-b316f6415318@intel.com
> Tested-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Thanks Sean!

Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>