diff options
| author | Sean Christopherson <seanjc@google.com> | 2025-09-19 14:16:49 -0700 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2025-09-23 08:55:20 -0700 |
| commit | 5b66e335ead6472f336b4d7d9cbf14488b844f27 (patch) | |
| tree | 544f6ea313ba14e26f884254dc89b0d5e5a346b5 | |
| parent | 4135a9a8ccba2b685f2301429ea765fa0f78eb89 (diff) | |
KVM: SEV: Reject non-positive effective lengths during LAUNCH_UPDATE
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>
| -rw-r--r-- | arch/x86/kvm/svm/sev.c | 2 | ||||
| -rw-r--r-- | virt/kvm/guest_memfd.c | 3 |
2 files changed, 3 insertions, 2 deletions
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index d2ffacd43234..019d920fe442 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -2353,7 +2353,7 @@ static int snp_launch_update(struct kvm *kvm, struct kvm_sev_cmd *argp) pr_debug("%s: GFN start 0x%llx length 0x%llx type %d flags %d\n", __func__, params.gfn_start, params.len, params.type, params.flags); - if (!PAGE_ALIGNED(params.len) || params.flags || + if (!params.len || !PAGE_ALIGNED(params.len) || params.flags || (params.type != KVM_SEV_SNP_PAGE_TYPE_NORMAL && params.type != KVM_SEV_SNP_PAGE_TYPE_ZERO && params.type != KVM_SEV_SNP_PAGE_TYPE_UNMEASURED && 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); |