linux-kernel - Re: [PATCH v8 08/30] KVM: selftests: TDX: Update load_td_memory_region() for VM memory backed by guest memfd

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aJpTMVV-F0z8iyb4@google.com>
Date: Mon, 11 Aug 2025 13:31:45 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sagi Shahar <sagis@...gle.com>
Cc: linux-kselftest@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>, 
	Shuah Khan <shuah@...nel.org>, Ackerley Tng <ackerleytng@...gle.com>, 
	Ryan Afranji <afranji@...gle.com>, Andrew Jones <ajones@...tanamicro.com>, 
	Isaku Yamahata <isaku.yamahata@...el.com>, Erdem Aktas <erdemaktas@...gle.com>, 
	Rick Edgecombe <rick.p.edgecombe@...el.com>, Roger Wang <runanwang@...gle.com>, 
	Binbin Wu <binbin.wu@...ux.intel.com>, Oliver Upton <oliver.upton@...ux.dev>, 
	"Pratik R. Sampat" <pratikrajesh.sampat@....com>, Reinette Chatre <reinette.chatre@...el.com>, 
	Ira Weiny <ira.weiny@...el.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v8 08/30] KVM: selftests: TDX: Update load_td_memory_region()
 for VM memory backed by guest memfd

On Thu, Aug 07, 2025, Sagi Shahar wrote:
> From: Ackerley Tng <ackerleytng@...gle.com>
> 
> If guest memory is backed by restricted memfd
> 
> + UPM is being used, hence encrypted memory region has to be
>   registered
> + Can avoid making a copy of guest memory before getting TDX to
>   initialize the memory region
> 
> Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
> Signed-off-by: Sagi Shahar <sagis@...gle.com>
> ---
>  .../selftests/kvm/lib/x86/tdx/tdx_util.c      | 38 +++++++++++++++----
>  1 file changed, 30 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c b/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c
> index bb074af4a476..e2bf9766dc03 100644
> --- a/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c
> +++ b/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c
> @@ -324,6 +324,21 @@ static void tdx_td_finalize_mr(struct kvm_vm *vm)
>  	tdx_ioctl(vm->fd, KVM_TDX_FINALIZE_VM, 0, NULL);
>  }
>  
> +/*
> + * Other ioctls
> + */
> +
> +/*
> + * Register a memory region that may contain encrypted data in KVM.
> + */

Drop these comments.

> +static void register_encrypted_memory_region(struct kvm_vm *vm,
> +					     struct userspace_mem_region *region)

This is a comically bad helper.  Any person that is at all familiar with KVM's
CoCo support, or that simply reads KVM's documentation, will expect this to
invoke KVM_MEMORY_ENCRYPT_REG_REGION.  And this is obviously doing much more than
"registering" an encrypted region.  Not to mention this helper doesn't need to
exist; it has _one_ caller, and the code is quite self-explanatory.

> +{
> +	vm_set_memory_attributes(vm, region->region.guest_phys_addr,
> +				 region->region.memory_size,
> +				 KVM_MEMORY_ATTRIBUTE_PRIVATE);
> +}
> +
>  /*
>   * TD creation/setup/finalization
>   */
> @@ -459,28 +474,35 @@ static void load_td_memory_region(struct kvm_vm *vm,
>  	if (!sparsebit_any_set(pages))
>  		return;
>  
> +	if (region->region.guest_memfd != -1)
> +		register_encrypted_memory_region(vm, region);
> +
>  	sparsebit_for_each_set_range(pages, i, j) {
>  		const uint64_t size_to_load = (j - i + 1) * vm->page_size;
>  		const uint64_t offset =
>  			(i - lowest_page_in_region) * vm->page_size;
>  		const uint64_t hva = hva_base + offset;
>  		const uint64_t gpa = gpa_base + offset;
> -		void *source_addr;
> +		void *source_addr = (void *)hva;
>  
>  		/*
>  		 * KVM_TDX_INIT_MEM_REGION ioctl cannot encrypt memory in place.
>  		 * Make a copy if there's only one backing memory source.
>  		 */
> -		source_addr = mmap(NULL, size_to_load, PROT_READ | PROT_WRITE,
> -				   MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> -		TEST_ASSERT(source_addr,
> -			    "Could not allocate memory for loading memory region");
> -
> -		memcpy(source_addr, (void *)hva, size_to_load);
> +		if (region->region.guest_memfd == -1) {

Oh, here's the "if".

> +			source_addr = mmap(NULL, size_to_load, PROT_READ | PROT_WRITE,
> +					   MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> +			TEST_ASSERT(source_addr,
> +				    "Could not allocate memory for loading memory region");
> +
> +			memcpy(source_addr, (void *)hva, size_to_load);
> +			memset((void *)hva, 0, size_to_load);
> +		}
>  
>  		tdx_init_mem_region(vm, source_addr, gpa, size_to_load);
>  
> -		munmap(source_addr, size_to_load);
> +		if (region->region.guest_memfd == -1)
> +			munmap(source_addr, size_to_load);
>  	}
>  }
>  
> -- 
> 2.51.0.rc0.155.g4a0f42376b-goog
>