On 18/09/2025 01.21, Zhuoying Cai wrote:
From: Collin Walling <[email protected]>
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 DER format),
and their respective lengths. All of this data should be encapsulated
within a Diag508SigVerifBlock.
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 Diag508SigVerifBlock.
The following values indicate failure:
0x0102: certificate not available
0x0202: component data is invalid
0x0302: signature is not in PKCS#7 format
0x0402: signature-verification failed
0x0502: length of Diag508SigVerifBlock is invalid
Signed-off-by: Collin Walling <[email protected]>
Signed-off-by: Zhuoying Cai <[email protected]>
---
docs/specs/s390x-secure-ipl.rst | 5 ++
include/hw/s390x/ipl/diag508.h | 23 +++++++
target/s390x/diag.c | 115 +++++++++++++++++++++++++++++++-
3 files changed, 142 insertions(+), 1 deletion(-)
diff --git a/docs/specs/s390x-secure-ipl.rst b/docs/specs/s390x-secure-ipl.rst
index 0919425e9a..eec368d17b 100644
--- a/docs/specs/s390x-secure-ipl.rst
+++ b/docs/specs/s390x-secure-ipl.rst
@@ -66,3 +66,8 @@ that requires assistance from QEMU.
Subcode 0 - query installed subcodes
Returns a 64-bit mask indicating which subcodes are supported.
+
+Subcode 1 - perform signature verification
+ Perform signature-verification on a signed component, using certificates
+ from the certificate store and leveraging qcrypto libraries to perform
+ this operation.
diff --git a/include/hw/s390x/ipl/diag508.h b/include/hw/s390x/ipl/diag508.h
index 6281ad8299..ad401cc867 100644
--- a/include/hw/s390x/ipl/diag508.h
+++ b/include/hw/s390x/ipl/diag508.h
@@ -11,5 +11,28 @@
#define S390X_DIAG508_H
#define DIAG_508_SUBC_QUERY_SUBC 0x0000
+#define DIAG_508_SUBC_SIG_VERIF 0x8000
+
+#define DIAG_508_RC_OK 0x0001
+#define DIAG_508_RC_NO_CERTS 0x0102
+#define DIAG_508_RC_INVAL_COMP_DATA 0x0202
+#define DIAG_508_RC_INVAL_PKCS7_SIG 0x0302
+#define DIAG_508_RC_FAIL_VERIF 0x0402
+#define DIAG_508_RC_INVAL_LEN 0x0502
+
+struct Diag508SigVerifBlock {
+ uint32_t length;
+ uint8_t reserved0[3];
+ uint8_t version;
+ uint32_t reserved[2];
+ uint8_t cert_store_index;
+ uint8_t reserved1[7];
+ uint64_t cert_len;
+ uint64_t comp_len;
+ uint64_t comp_addr;
+ uint64_t sig_len;
+ uint64_t sig_addr;
+};
+typedef struct Diag508SigVerifBlock Diag508SigVerifBlock;
#endif
diff --git a/target/s390x/diag.c b/target/s390x/diag.c
index ee64257dbc..379fb8f2b4 100644
--- a/target/s390x/diag.c
+++ b/target/s390x/diag.c
@@ -602,9 +602,112 @@ void handle_diag_320(CPUS390XState *env, uint64_t r1,
uint64_t r3, uintptr_t ra)
}
}
+static int diag_508_verify_sig(uint8_t *cert, size_t cert_size,
+ uint8_t *comp, size_t comp_size,
+ uint8_t *sig, size_t sig_size)
+{
+ g_autofree uint8_t *sig_pem = NULL;
+ size_t sig_size_pem;
+ int rc;
+
+ /*
+ * PKCS#7 signature with DER format
+ * Convert to PEM format for signature verification
+ */
+ rc = qcrypto_pkcs7_convert_sig_pem(sig, sig_size, &sig_pem, &sig_size_pem,
NULL);
+ if (rc < 0) {
+ return -1;
+ }
+
+ rc = qcrypto_x509_verify_sig(cert, cert_size,
+ comp, comp_size,
+ sig_pem, sig_size_pem, NULL);
+ if (rc < 0) {
+ return -1;
+ }
+
+ return 0;
+}
+
+static int handle_diag508_sig_verif(uint64_t addr, size_t svb_size,
+ S390IPLCertificateStore *qcs)
+{
+ int rc;
+ int verified;
+ uint32_t svb_len;
+ uint64_t comp_len, comp_addr;
+ uint64_t sig_len, sig_addr;
+ g_autofree uint8_t *svb_comp = NULL;
+ g_autofree uint8_t *svb_sig = NULL;
+ g_autofree Diag508SigVerifBlock *svb = NULL;
+
+ if (!qcs || !qcs->count) {
+ return DIAG_508_RC_NO_CERTS;
+ }
+
+ svb = g_new0(Diag508SigVerifBlock, 1);
+ cpu_physical_memory_read(addr, svb, svb_size);
+
+ svb_len = be32_to_cpu(svb->length);
+ if (svb_len != svb_size) {
+ return DIAG_508_RC_INVAL_LEN;
+ }
+
+ 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;
+ }
I think there should also be something like an upper limit for comp_len and
sign_len here. Otherwise a malicious guest could force QEMU into allocating
giga- or terabytes of memory here to cause out-of-memory situations in the host.
+ 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
+ *
+ * Ignore errors from signature format convertion and verification,
+ * because currently in the certificate lookup process.
The second half of above sentence looks incomplete?
+ *
+ * Any error is treated as a verification failure,
+ * and the final result (verified or not) will be reported later.
+ */
+ for (int i = 0; i < qcs->count; i++) {
+ verified = diag_508_verify_sig(qcs->certs[i].raw,
+ qcs->certs[i].size,
+ svb_comp, comp_len,
+ svb_sig, sig_len);
+ if (verified == 0) {
+ svb->cert_store_index = i;
+ svb->cert_len = cpu_to_be64(qcs->certs[i].der_size);
+ cpu_physical_memory_write(addr, svb, be32_to_cpu(svb_size));
+ rc = DIAG_508_RC_OK;
+ break;
+ }
+ }
+
+ return rc;
+}
Thomas
