On 1/9/23 10:08, Peter Gonda wrote:

KVM_SEV_SEND_UPDATE_DATA and KVM_SEV_RECEIVE_UPDATE_DATA have an integer overflow issue. Params.guest_len and offset are both 32bite wide, with a large params.guest_len the check to confirm a page boundary is not crossed can falsely pass:

 /* Check if we are crossing the page boundary *
 offset = params.guest_uaddr & (PAGE_SIZE - 1);
 if ((params.guest_len + offset > PAGE_SIZE))

Add an additional check to this conditional to confirm that params.guest_len itself is not greater than PAGE_SIZE.

The current code is can only overflow with a params.guest_len of greater than 0xfffff000. And the FW spec says these commands fail with lengths greater than 16KB. So this issue should not be a security concern

Fixes: 15fb7de1a7f5 ("KVM: SVM: Add KVM_SEV_RECEIVE_UPDATE_DATA command") Fixes: d3d1af85e2c7 ("KVM: SVM: Add KVM_SEND_UPDATE_DATA command") Reported-by: Andy Nguyen theflow@google.com Suggested-by: Thomas Lendacky thomas.lendacky@amd.com Signed-off-by: Peter Gonda pgonda@google.com Cc: David Rientjes rientjes@google.com Cc: Paolo Bonzini pbonzini@redhat.com Cc: Sean Christopherson seanjc@google.com Cc: kvm@vger.kernel.org Cc: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org

---

arch/x86/kvm/svm/sev.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 273cba809328..9451de72f917 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -1294,7 +1294,7 @@ static int sev_send_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp) /* Check if we are crossing the page boundary */ offset = params.guest_uaddr & (PAGE_SIZE - 1);

• if ((params.guest_len + offset > PAGE_SIZE))

• if (params.guest_len > PAGE_SIZE || (params.guest_len + offset > PAGE_SIZE))

I see the original if statement had double parentheses, which looks strange. Should this if (and the one below) be:

if (params.guest_len > PAGE_SIZE || (params.guest_len + offset) > PAGE_SIZE)

Thanks, Tom

return -EINVAL;

/* Pin guest memory */ @@ -1474,7 +1474,7 @@ static int sev_receive_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp) /* Check if we are crossing the page boundary */ offset = params.guest_uaddr & (PAGE_SIZE - 1);

• if ((params.guest_len + offset > PAGE_SIZE))

• if (params.guest_len > PAGE_SIZE || (params.guest_len + offset > PAGE_SIZE)) return -EINVAL;

hdr = psp_copy_user_blob(params.hdr_uaddr, params.hdr_len);