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'. Cc: Thomas Lendacky <thomas.lendacky@xxxxxxx> Cc: Michael Roth <michael.roth@xxxxxxx> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> --- Compile tested only. Came across this when trying to figure out how to handle the batching of gmem post-populate calls. arch/x86/kvm/svm/sev.c | 2 ++ virt/kvm/guest_memfd.c | 3 ++- 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index f4381878a9e5..746a57bf1f71 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -2360,6 +2360,8 @@ static int snp_launch_update(struct kvm *kvm, struct kvm_sev_cmd *argp) return -EINVAL; npages = params.len / PAGE_SIZE; + if (npages <= 0) + return -EINVAL; /* * For each GFN that's being prepared as part of the initial guest diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 7d85cc33c0bb..79552467add5 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -639,7 +639,8 @@ long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long long i; lockdep_assert_held(&kvm->slots_lock); - if (npages < 0) + + if (WARN_ON_ONCE(npages <= 0)) return -EINVAL; slot = gfn_to_memslot(kvm, start_gfn); base-commit: ecbcc2461839e848970468b44db32282e5059925 -- 2.51.0.268.g9569e192d0-goog
