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Check for an invalid length during LAUNCH_UPDATE at the start of snp_launch_update() instead of subtly relying on kvm_gmem_populate() to detect the bad state. Code that directly handles userspace input absolutely should sanitize those inputs; failure to do so is asking for bugs where KVM consumes an invalid "npages". Keep the check in gmem, but wrap it in a WARN to flag any bad usage by the caller. Note, this is technically an ABI change as KVM would previously allow a length of '0'. But allowing a length of '0' is nonsensical and creates pointless conundrums in KVM. E.g. an empty range is arguably neither private nor shared, but LAUNCH_UPDATE will fail if the starting gpa can't be made private. In practice, no known or well-behaved VMM passes a length of '0'. Note #2, the PAGE_ALIGNED(params.len) check ensures that lengths between 1 and 4095 (inclusive) are also rejected, i.e. that KVM won't end up with npages=0 when doing "npages = params.len / PAGE_SIZE". Cc: Thomas Lendacky <thomas.lendacky@amd.com> Cc: Michael Roth <michael.roth@amd.com> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com> Link: https://lore.kernel.org/r/20250919211649.1575654-1-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.