[PATCH 6.2 0833/1001] KVM: SVM: Fix potential overflow in SEVs send|receive_update_data()

[Greg Kroah-Hartman]

From: Peter Gonda <pgonda@xxxxxxxxxx>

commit f94f053aa3a5d6ff17951870483d9eb9e13de2e2 upstream.

KVM_SEV_SEND_UPDATE_DATA and KVM_SEV_RECEIVE_UPDATE_DATA have an integer
overflow issue. Params.guest_len and offset are both 32 bits 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 confirm that params.guest_len itself is not
greater than PAGE_SIZE.

Note, this isn't a security concern as overflow can happen if and only if
params.guest_len is greater than 0xfffff000, and the FW spec says these
commands fail with lengths greater than 16KB, i.e. the PSP will detect
KVM's goof.

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@xxxxxxxxxx>
Suggested-by: Thomas Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Peter Gonda <pgonda@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Link: https://lore.kernel.org/r/20230207171354.4012821-1-pgonda@xxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/kvm/svm/sev.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1293,7 +1293,7 @@ static int sev_send_update_data(struct k
 
 	/* 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;
 
 	/* Pin guest memory */
@@ -1473,7 +1473,7 @@ static int sev_receive_update_data(struc
 
 	/* 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);