Re: [PATCH v3 12/28] s390x/diag: Implement DIAG 508 subcode 1 for signature verification

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Jun 04, 2025 at 05:56:40PM -0400, Zhuoying Cai wrote:
> From: Collin Walling <walling@linux.ibm.com>
> 
> DIAG 508 subcode 1 performs signature-verification on signed components.
> A signed component may be a Linux kernel image, or any other signed
> binary. **Verification of initrd is not supported.**
> 
> The instruction call expects two item-pairs: an address of a device
> component, an address of the analogous signature file (in PKCS#7 format),
> and their respective lengths. All of this data should be encapsulated
> within a Diag508SignatureVerificationBlock, with the CertificateStoreInfo
> fields ignored. The DIAG handler will read from the provided addresses
> to retrieve the necessary data, parse the signature file, then
> perform the signature-verification. Because there is no way to
> correlate a specific certificate to a component, each certificate
> in the store is tried until either verification succeeds, or all
> certs have been exhausted.
> 
> The subcode value is denoted by setting the second-to-left-most bit of
> a 2-byte field.
> 
> A return code of 1 indicates success, and the index and length of the
> corresponding certificate will be set in the CertificateStoreInfo
> portion of the SigVerifBlock. The following values indicate failure:
> 
> 	0x0202: component data is invalid
> 	0x0302: signature is not in PKCS#7 format
> 	0x0402: signature-verification failed
> 
> Signed-off-by: Collin Walling <walling@linux.ibm.com>
> Signed-off-by: Zhuoying Cai <zycai@linux.ibm.com>


> diff --git a/target/s390x/diag.c b/target/s390x/diag.c
> index 1ef1eb5299..ca7dd0f2e6 100644
> --- a/target/s390x/diag.c
> +++ b/target/s390x/diag.c
> @@ -526,9 +526,81 @@ void handle_diag_320(CPUS390XState *env, uint64_t r1, uint64_t r3, uintptr_t ra)
>      env->regs[r1 + 1] = rc;
>  }
>  
> +static int handle_diag508_sig_verif(uint64_t addr, size_t csi_size, size_t svb_size,
> +                                    S390IPLCertificateStore *qcs)
> +{
> +    int rc;
> +    int verified;
> +    Error *err;
> +    uint64_t comp_len, comp_addr;
> +    uint64_t sig_len, sig_addr;
> +    g_autofree uint8_t *svb_comp;
> +    g_autofree uint8_t *svb_sig;
> +    g_autofree Diag508SignatureVerificationBlock *svb;

All g_auto* variables must be initialized to NULL at time
of declaration. As written this results in freeing of
unitialized data if a 'return' is hit before these are
initialized.

> +
> +    if (!qcs || !qcs->count) {
> +        return DIAG_508_RC_NO_CERTS;
> +    }
> +
> +    svb = g_new0(Diag508SignatureVerificationBlock, 1);
> +    cpu_physical_memory_read(addr, svb, svb_size);
> +
> +    comp_len = be64_to_cpu(svb->comp_len);
> +    comp_addr = be64_to_cpu(svb->comp_addr);
> +    sig_len = be64_to_cpu(svb->sig_len);
> +    sig_addr = be64_to_cpu(svb->sig_addr);
> +
> +    if (!comp_len || !comp_addr) {
> +        return DIAG_508_RC_INVAL_COMP_DATA;
> +    }
> +
> +    if (!sig_len || !sig_addr) {
> +        return DIAG_508_RC_INVAL_PKCS7_SIG;
> +    }
> +
> +    svb_comp = g_malloc0(comp_len);
> +    cpu_physical_memory_read(comp_addr, svb_comp, comp_len);
> +
> +    svb_sig = g_malloc0(sig_len);
> +    cpu_physical_memory_read(sig_addr, svb_sig, sig_len);
> +
> +    rc = DIAG_508_RC_FAIL_VERIF;
> +    /*
> +     * It is uncertain which certificate contains
> +     * the analogous key to verify the signed data
> +     */
> +    for (int i = 0; i < qcs->count; i++) {
> +        err = NULL;
> +        verified = qcrypto_verify_x509_cert((uint8_t *)qcs->certs[i].raw,
> +                                            qcs->certs[i].size,
> +                                            svb_comp, comp_len,
> +                                            svb_sig, sig_len, &err);
> +
> +        /* return early if GNUTLS is not enabled */
> +        if (verified == -ENOTSUP) {
> +            break;
> +        }

All errors must be honoured not merely missing gnutls, and this code
leaks 'err' too

> +
> +        if (verified == 0) {
> +            svb->csi.idx = i;
> +            svb->csi.len = cpu_to_be64(qcs->certs[i].size);
> +            cpu_physical_memory_write(addr, &svb->csi, be32_to_cpu(csi_size));
> +            rc = DIAG_508_RC_OK;
> +            break;
> +       }
> +    }
> +
> +    return rc;
> +}

With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|