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    SubjectRe: [PATCH v8 3/4] virt: sev-guest: Remove err in handle_guest_request
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    On 11/4/22 18:00, Dionna Glaze wrote:
    > The err variable may not be set in the call to snp_issue_guest_request,
    > yet it is unconditionally written back to fw_err if fw_err is non-null.
    > This is undefined behavior, and currently returns uninitialized kernel
    > stack memory to user space.
    >
    > The fw_err argument is better to just pass through to
    > snp_issue_guest_request, so we do that by passing along the ioctl
    > argument. This removes the need for an argument to handle_guest_request.
    >
    > Cc: Tom Lendacky <Thomas.Lendacky@amd.com>
    > Cc: Paolo Bonzini <pbonzini@redhat.com>
    > Cc: Joerg Roedel <jroedel@suse.de>
    > Cc: Peter Gonda <pgonda@google.com>
    > Cc: Thomas Gleixner <tglx@linutronix.de>
    > Cc: Dave Hansen <dave.hansen@linux.intel.com>
    > Cc: Borislav Petkov <bp@suse.de>
    > Cc: Haowen Bai <baihaowen@meizu.com>
    > Cc: Liam Merwick <liam.merwick@oracle.com>
    > Cc: Yang Yingliang <yangyingliang@huawei.com>
    >
    > Fixes: fce96cf04430 ("virt: Add SEV-SNP guest driver")
    > Signed-off-by: Dionna Glaze <dionnaglaze@google.com>

    Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>

    > ---
    > drivers/virt/coco/sev-guest/sev-guest.c | 37 ++++++++++++-------------
    > 1 file changed, 18 insertions(+), 19 deletions(-)
    >
    > diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
    > index d08ff87c2dac..5615d349b378 100644
    > --- a/drivers/virt/coco/sev-guest/sev-guest.c
    > +++ b/drivers/virt/coco/sev-guest/sev-guest.c
    > @@ -320,11 +320,11 @@ static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8
    > return __enc_payload(snp_dev, req, payload, sz);
    > }
    >
    > -static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, int msg_ver,
    > +static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
    > + struct snp_guest_request_ioctl *arg,
    > u8 type, void *req_buf, size_t req_sz, void *resp_buf,
    > - u32 resp_sz, __u64 *fw_err)
    > + u32 resp_sz)
    > {
    > - unsigned long err;
    > u64 seqno;
    > int rc;
    >
    > @@ -336,12 +336,14 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
    > memset(snp_dev->response, 0, sizeof(struct snp_guest_msg));
    >
    > /* Encrypt the userspace provided payload */
    > - rc = enc_payload(snp_dev, seqno, msg_ver, type, req_buf, req_sz);
    > + rc = enc_payload(snp_dev, seqno, arg->msg_version, type, req_buf,
    > + req_sz);
    > if (rc)
    > return rc;
    >
    > /* Call firmware to process the request */
    > - rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
    > + rc = snp_issue_guest_request(exit_code, &snp_dev->input,
    > + &arg->fw_err);
    >
    > /*
    > * If the extended guest request fails due to having to small of a
    > @@ -349,23 +351,21 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
    > * extended data request.
    > */
    > if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST &&
    > - err == SNP_GUEST_REQ_INVALID_LEN) {
    > + arg->fw_err == SNP_GUEST_REQ_INVALID_LEN) {
    > const unsigned int certs_npages = snp_dev->input.data_npages;
    >
    > exit_code = SVM_VMGEXIT_GUEST_REQUEST;
    > - rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
    > + rc = snp_issue_guest_request(exit_code, &snp_dev->input,
    > + &arg->fw_err);
    >
    > - err = SNP_GUEST_REQ_INVALID_LEN;
    > + arg->fw_err = SNP_GUEST_REQ_INVALID_LEN;
    > snp_dev->input.data_npages = certs_npages;
    > }
    >
    > - if (fw_err)
    > - *fw_err = err;
    > -
    > if (rc) {
    > dev_alert(snp_dev->dev,
    > "Detected error from ASP request. rc: %d, fw_err: %llu\n",
    > - rc, *fw_err);
    > + rc, arg->fw_err);
    > goto disable_vmpck;
    > }
    >
    > @@ -412,9 +412,9 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
    > if (!resp)
    > return -ENOMEM;
    >
    > - rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg->msg_version,
    > + rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg,
    > SNP_MSG_REPORT_REQ, &req, sizeof(req), resp->data,
    > - resp_len, &arg->fw_err);
    > + resp_len);
    > if (rc)
    > goto e_free;
    >
    > @@ -452,9 +452,8 @@ static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_reque
    > if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
    > return -EFAULT;
    >
    > - rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg->msg_version,
    > - SNP_MSG_KEY_REQ, &req, sizeof(req), buf, resp_len,
    > - &arg->fw_err);
    > + rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg,
    > + SNP_MSG_KEY_REQ, &req, sizeof(req), buf, resp_len);
    > if (rc)
    > return rc;
    >
    > @@ -514,9 +513,9 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
    > return -ENOMEM;
    >
    > snp_dev->input.data_npages = npages;
    > - ret = handle_guest_request(snp_dev, SVM_VMGEXIT_EXT_GUEST_REQUEST, arg->msg_version,
    > + ret = handle_guest_request(snp_dev, SVM_VMGEXIT_EXT_GUEST_REQUEST, arg,
    > SNP_MSG_REPORT_REQ, &req.data,
    > - sizeof(req.data), resp->data, resp_len, &arg->fw_err);
    > + sizeof(req.data), resp->data, resp_len);
    >
    > /* If certs length is invalid then copy the returned length */
    > if (arg->fw_err == SNP_GUEST_REQ_INVALID_LEN) {

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