KVM: SEV: Explicitly disallow NULL user address for SNP_LAUNCH_UPDATE

Explicitly reject a NULL userspace virtual address for the source page of
SNP_LAUNCH_UPDATE instead of relying on the post-populate callback to do
the check, and don't WARN on failure, as the scenario is blatantly user-
triggerable, as reported by Sashiko.  Waiting until post-populate to check
the address "works", but makes it unnecessarily difficult to see that KVM's
ABI is to disallow a NULL source page for non-ZERO pages.

Note, several existing VMMs pass a valid userspace address for the ZERO
case, i.e. KVM can't *require* the userspace address to be NULL for ZERO
pages, at least not without breaking userspace.

Fixes: dee5a47cc7a4 ("KVM: SEV: Add KVM_SEV_SNP_LAUNCH_UPDATE command")
Reported-by: Sashiko Bot <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/20260611125849.9ED631F00893@smtp.kernel.org
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Link: https://patch.msgid.link/20260630213711.479692-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

0 files changed, 0 insertions, 0 deletions