Re: [PATCH] KVM: sev: Fix int overflow in send|recieve_update_data ioctls

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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@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
---
  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);



[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]

  Powered by Linux