[PULL 16/37] s390x/diag: Implement DIAG 508 subcode 1 for signature verification

[Eric Farman <farman@linux.ibm.com>]

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 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.

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: no certificates are available in the store
	0x0202: component data is invalid
	0x0302: PKCS#7 format signature is invalid
	0x0402: signature-verification failed
	0x0502: length of Diag508SigVerifBlock is invalid

Signed-off-by: Collin Walling <walling@linux.ibm.com>
Signed-off-by: Zhuoying Cai <zycai@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20260730214624.2328883-15-zycai@linux.ibm.com
Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 docs/specs/s390x-secure-ipl.rst |  17 +++++
 include/hw/s390x/ipl/diag508.h  |  30 +++++++++
 target/s390x/diag.c             | 114 +++++++++++++++++++++++++++++++-
 3 files changed, 160 insertions(+), 1 deletion(-)

diff --git a/docs/specs/s390x-secure-ipl.rst b/docs/specs/s390x-secure-ipl.rst
index 776270d816..d8dcc77ba2 100644
--- a/docs/specs/s390x-secure-ipl.rst
+++ b/docs/specs/s390x-secure-ipl.rst
@@ -84,3 +84,20 @@ 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.
+
+    Note: verification of initrd is not supported.
+
+    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``: no certificates are available in the store
+    * ``0x0202``: component data is invalid
+    * ``0x0302``: PKCS#7 format signature is invalid
+    * ``0x0402``: signature-verification failed
+    * ``0x0502``: length of Diag508SigVerifBlock is invalid
diff --git a/include/hw/s390x/ipl/diag508.h b/include/hw/s390x/ipl/diag508.h
index 6281ad8299..bd967954b9 100644
--- a/include/hw/s390x/ipl/diag508.h
+++ b/include/hw/s390x/ipl/diag508.h
@@ -11,5 +11,35 @@
 #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
+
+/*
+ * Maximum component and signature sizes for current secure boot implementation
+ * Not architecturally defined and may need to revisit if increased
+ */
+#define DIAG_508_MAX_COMP_LEN      0x10000000
+#define DIAG_508_MAX_SIG_LEN       4096
+
+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 c71c1a7769..f465a2eed2 100644
--- a/target/s390x/diag.c
+++ b/target/s390x/diag.c
@@ -12,6 +12,7 @@
  * GNU General Public License for more details.
  */
 
+#include <inttypes.h>
 #include "qemu/osdep.h"
 #include "cpu.h"
 #include "s390x-internal.h"
@@ -620,9 +621,112 @@ void handle_diag_320(CPUS390XState *env, uint64_t r1, uint64_t r3, uintptr_t ra)
     }
 }
 
+static bool 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
+     *
+     * Ignore errors during qcrypto signature format conversion and verification
+     * Return false on any error, treating it as a verification failure
+     */
+    rc = qcrypto_pkcs7_convert_sig_pem(sig, sig_size, &sig_pem, &sig_size_pem, NULL);
+    if (rc < 0) {
+        return false;
+    }
+
+    rc = qcrypto_x509_verify_sig(cert, cert_size,
+                                 comp, comp_size,
+                                 sig_pem, sig_size_pem, NULL);
+    if (rc < 0) {
+        return false;
+    }
+
+    return true;
+}
+
+static int handle_diag508_sig_verif(CPUS390XState *env, uint64_t addr)
+{
+    int verified;
+    uint32_t svb_len;
+    uint64_t comp_len, comp_addr;
+    uint64_t sig_len, sig_addr;
+    g_autofree uint8_t *comp = NULL;
+    g_autofree uint8_t *sig = NULL;
+    g_autofree Diag508SigVerifBlock *svb = NULL;
+    size_t svb_size = sizeof(Diag508SigVerifBlock);
+    S390IPLCertificateStore *cs = s390_ipl_get_certificate_store();
+
+    if (!cs->count) {
+        return DIAG_508_RC_NO_CERTS;
+    }
+
+    svb = g_new0(Diag508SigVerifBlock, 1);
+    s390_ipl_read(env, 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 || comp_len > DIAG_508_MAX_COMP_LEN) {
+        if (comp_len > DIAG_508_MAX_COMP_LEN) {
+            warn_report("DIAG 0x508: component length %" PRIu64
+                        " exceeds current maximum %u",
+                        comp_len, DIAG_508_MAX_COMP_LEN);
+        }
+        return DIAG_508_RC_INVAL_COMP_DATA;
+    }
+
+    if (!sig_len || !sig_addr || sig_len > DIAG_508_MAX_SIG_LEN) {
+        if (sig_len > DIAG_508_MAX_SIG_LEN) {
+            warn_report("DIAG 0x508: signature length %" PRIu64
+                        " exceeds current maximum %u",
+                        sig_len, DIAG_508_MAX_SIG_LEN);
+        }
+        return DIAG_508_RC_INVAL_PKCS7_SIG;
+    }
+
+    comp = g_malloc0(comp_len);
+    s390_ipl_read(env, comp_addr, comp, comp_len);
+
+    sig = g_malloc0(sig_len);
+    s390_ipl_read(env, sig_addr, sig, sig_len);
+
+    for (int i = 0; i < cs->count; i++) {
+        verified = diag_508_verify_sig(cs->certs[i].raw,
+                                       cs->certs[i].size,
+                                       comp, comp_len,
+                                       sig, sig_len);
+        if (verified) {
+            svb->cert_store_index = i;
+            svb->cert_len = cpu_to_be64(cs->certs[i].der_size);
+            s390_ipl_write(env, addr, svb, svb_size);
+            return DIAG_508_RC_OK;
+        }
+    }
+
+    return DIAG_508_RC_FAIL_VERIF;
+}
+
+QEMU_BUILD_BUG_MSG(sizeof(Diag508SigVerifBlock) != 64,
+                   "size of Diag508SigVerifBlock is wrong");
+
 void handle_diag_508(CPUS390XState *env, uint64_t r1, uint64_t r3, uintptr_t ra)
 {
     uint64_t subcode = env->regs[r3];
+    uint64_t addr = env->regs[r1];
     int rc;
 
     if (env->psw.mask & PSW_MASK_PSTATE) {
@@ -637,7 +741,15 @@ void handle_diag_508(CPUS390XState *env, uint64_t r1, uint64_t r3, uintptr_t ra)
 
     switch (subcode) {
     case DIAG_508_SUBC_QUERY_SUBC:
-        rc = 0;
+        rc = DIAG_508_SUBC_SIG_VERIF;
+        break;
+    case DIAG_508_SUBC_SIG_VERIF:
+        if (!diag_parm_addr_valid(addr, sizeof(Diag508SigVerifBlock), true)) {
+            s390_program_interrupt(env, PGM_ADDRESSING, ra);
+            return;
+        }
+
+        rc = handle_diag508_sig_verif(env, addr);
         break;
     default:
         s390_program_interrupt(env, PGM_SPECIFICATION, ra);
-- 
2.55.0