linux-kernel - [PATCH v2 3/5] KVM: SEV: Document/enforce page-alignment for KVM_SEV_SNP_LAUNCH

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Message-ID: <20251215153411.3613928-4-michael.roth@amd.com>
Date: Mon, 15 Dec 2025 09:34:09 -0600
From: Michael Roth <michael.roth@....com>
To: <kvm@...r.kernel.org>
CC: <linux-coco@...ts.linux.dev>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, <thomas.lendacky@....com>,
	<pbonzini@...hat.com>, <seanjc@...gle.com>, <vbabka@...e.cz>,
	<ashish.kalra@....com>, <liam.merwick@...cle.com>, <david@...hat.com>,
	<vannapurve@...gle.com>, <ackerleytng@...gle.com>, <aik@....com>,
	<ira.weiny@...el.com>, <yan.y.zhao@...el.com>
Subject: [PATCH v2 3/5] KVM: SEV: Document/enforce page-alignment for KVM_SEV_SNP_LAUNCH_UPDATE

In the past, KVM_SEV_SNP_LAUNCH_UPDATE accepted a non-page-aligned
'uaddr' parameter to copy data from, but continuing to support this with
new functionality like in-place conversion and hugepages in the pipeline
has proven to be more trouble than it is worth, since there are no known
users that have been identified who use a non-page-aligned 'uaddr'
parameter.

Rather than locking guest_memfd into continuing to support this, go
ahead and document page-alignment as a requirement and begin enforcing
this in the handling function.

Signed-off-by: Michael Roth <michael.roth@....com>
---
 Documentation/virt/kvm/x86/amd-memory-encryption.rst | 2 +-
 arch/x86/kvm/svm/sev.c                               | 6 +++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/Documentation/virt/kvm/x86/amd-memory-encryption.rst b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
index 1ddb6a86ce7f..5a88d0197cb3 100644
--- a/Documentation/virt/kvm/x86/amd-memory-encryption.rst
+++ b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
@@ -523,7 +523,7 @@ Returns: 0 on success, < 0 on error, -EAGAIN if caller should retry
 
         struct kvm_sev_snp_launch_update {
                 __u64 gfn_start;        /* Guest page number to load/encrypt data into. */
-                __u64 uaddr;            /* Userspace address of data to be loaded/encrypted. */
+                __u64 uaddr;            /* 4k-aligned address of data to be loaded/encrypted. */
                 __u64 len;              /* 4k-aligned length in bytes to copy into guest memory.*/
                 __u8 type;              /* The type of the guest pages being initialized. */
                 __u8 pad0;
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 362c6135401a..90c512ca24a9 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2366,6 +2366,11 @@ static int snp_launch_update(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	     params.type != KVM_SEV_SNP_PAGE_TYPE_CPUID))
 		return -EINVAL;
 
+	src = params.type == KVM_SEV_SNP_PAGE_TYPE_ZERO ? NULL : u64_to_user_ptr(params.uaddr);
+
+	if (!PAGE_ALIGNED(src))
+		return -EINVAL;
+
 	npages = params.len / PAGE_SIZE;
 
 	/*
@@ -2397,7 +2402,6 @@ static int snp_launch_update(struct kvm *kvm, struct kvm_sev_cmd *argp)
 
 	sev_populate_args.sev_fd = argp->sev_fd;
 	sev_populate_args.type = params.type;
-	src = params.type == KVM_SEV_SNP_PAGE_TYPE_ZERO ? NULL : u64_to_user_ptr(params.uaddr);
 
 	count = kvm_gmem_populate(kvm, params.gfn_start, src, npages,
 				  sev_gmem_post_populate, &sev_populate_args);
-- 
2.25.1