linux-kernel - [PATCH 6.2 0833/1001] KVM: SVM: Fix potential overflow in SEVs send|receive_update

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Message-Id: <20230307170057.940444308@linuxfoundation.org>
Date:   Tue,  7 Mar 2023 18:00:05 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     stable@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        patches@...ts.linux.dev, Andy Nguyen <theflow@...gle.com>,
        Thomas Lendacky <thomas.lendacky@....com>,
        Peter Gonda <pgonda@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 6.2 0833/1001] KVM: SVM: Fix potential overflow in SEVs send|receive_update_data()

From: Peter Gonda <pgonda@...gle.com>

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@...gle.com>
Suggested-by: Thomas Lendacky <thomas.lendacky@....com>
Signed-off-by: Peter Gonda <pgonda@...gle.com>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org
Cc: stable@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
Link: https://lore.kernel.org/r/20230207171354.4012821-1-pgonda@google.com
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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);