On 4/11/25 10:38 AM, Thomas Huth wrote:
> On 08/04/2025 17.55, Zhuoying Cai wrote:
>> From: Collin Walling <[email protected]>
>>
>> DIAG 508 subcode 2 performs signature-verfication 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:
>>
>> 0x0402: component data is invalid
>> 0x0502: certificate is not in x509 format
>> 0x0602: signature is not in PKCS#7 format
>> 0x0702: signature-verification failed
>>
>> Signed-off-by: Collin Walling <[email protected]>
>> ---
>> include/hw/s390x/ipl/diag508.h | 25 +++++++
>> target/s390x/diag.c | 131 ++++++++++++++++++++++++++++++++-
>> 2 files changed, 155 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/hw/s390x/ipl/diag508.h b/include/hw/s390x/ipl/diag508.h
>> index 83c4439cb2..f8f4b6398e 100644
>> --- a/include/hw/s390x/ipl/diag508.h
>> +++ b/include/hw/s390x/ipl/diag508.h
>> @@ -13,5 +13,30 @@
>> #define S390X_DIAG508_H
>>
>> #define DIAG_508_SUBC_QUERY_SUBC 0x0000
>> +#define DIAG_508_SUBC_SIG_VERIF 0x4000
>> +
>> +#define DIAG_508_RC_OK 0x0001
>> +#define DIAG_508_RC_NO_CERTS 0x0102
>> +#define DIAG_508_RC_CERT_NOT_FOUND 0x0202
>> +#define DIAG_508_RC_NO_MEM_FOR_CERT 0x0302
>> +#define DIAG_508_RC_INVAL_COMP_DATA 0x0402
>> +#define DIAG_508_RC_INVAL_X509_CERT 0x0502
>> +#define DIAG_508_RC_INVAL_PKCS7_SIG 0x0602
>> +#define DIAG_508_RC_FAIL_VERIF 0x0702
>> +
>> +struct Diag508CertificateStoreInfo {
>> + uint8_t idx;
>> + uint64_t len;
>> +} QEMU_PACKED;
>> +typedef struct Diag508CertificateStoreInfo Diag508CertificateStoreInfo;
>> +
>> +struct Diag508SignatureVerificationBlock {
>> + Diag508CertificateStoreInfo csi;
>> + uint64_t comp_len;
>> + uint64_t comp_addr;
>> + uint64_t sig_len;
>> + uint64_t sig_addr;
>> +} QEMU_PACKED;
>> +typedef struct Diag508SignatureVerificationBlock
>> Diag508SignatureVerificationBlock;
>>
>> #endif
>> diff --git a/target/s390x/diag.c b/target/s390x/diag.c
>> index ad7f4b5025..cecb8bf130 100644
>> --- a/target/s390x/diag.c
>> +++ b/target/s390x/diag.c
>> @@ -25,6 +25,11 @@
>> #include "target/s390x/kvm/pv.h"
>> #include "qemu/error-report.h"
>>
>> +#ifdef CONFIG_GNUTLS
>> +#include <gnutls/x509.h>
>> +#include <gnutls/gnutls.h>
>> +#include <gnutls/pkcs7.h>
>> +#endif /* CONFIG_GNUTLS */
>>
>> int handle_diag_288(CPUS390XState *env, uint64_t r1, uint64_t r3)
>> {
>> @@ -489,9 +494,67 @@ void handle_diag_320(CPUS390XState *env, uint64_t r1,
>> uint64_t r3, uintptr_t ra)
>> env->regs[r1 + 1] = rc;
>> }
>>
>> +#ifdef CONFIG_GNUTLS
>> +#define datum_init(datum, data, size) \
>> + datum = (gnutls_datum_t){data, size}
>> +
>> +static int diag_508_init_comp(gnutls_datum_t *comp,
>> + Diag508SignatureVerificationBlock *svb)
>> +{
>> + uint8_t *svb_comp = NULL;
>> +
>> + if (!svb->comp_len || !svb->comp_addr) {
>> + error_report("No component data.");
>> + return -1;
>> + }
>> +
>> + /*
>> + * corrupted size vs. prev_size in fastbins, occurs during 2nd
>> iteration,
>> + * allocating 1mil bytes.
>
> I don't understand that comment - could you elaborate?
>
Elaboration: developer (me) forgot to remove this comment from an early
implementation. It is irrelevant to the code presented here, sorry.
If you're curious:
<irrelevant>
I may be incorrect here, but from what I was able to gather, this issue
was encountered during a memory allocation, specifically without
properly freeing the previous component.
When allocating memory for the 2nd component (also the 2nd
invocation/iteration of this function), I would see the "corrupted size
vs prev_size in fastbins" error. I think this is because the previous
component wasn't properly freed and there was a conflict between the
amount of space needed for the new component and however much was
available in the fastbins... debugging showed it was requesting 1mil bytes.
This has been corrected.
</irrelevant>
>> + */
>> + svb_comp = g_malloc0(svb->comp_len);
>> + cpu_physical_memory_read(svb->comp_addr, svb_comp, svb->comp_len);
>> +
>> + /*
>> + * Component data is not written back to the caller,
>> + * so no need to do a deep copy. Comp is freed when
>> + * svb is freed.
>> + */
>> + datum_init(*comp, svb_comp, svb->comp_len);
>> + return 0;
>> +}
>> +
>> +static int diag_508_init_signature(gnutls_pkcs7_t *sig,
>> + Diag508SignatureVerificationBlock *svb)
>> +{
>> + gnutls_datum_t datum_sig;
>> + uint8_t *svb_sig = NULL;
>> +
>> + if (!svb->sig_len || !svb->sig_addr) {
>> + error_report("No signature data");
>> + return -1;
>> + }
>> +
>> + svb_sig = g_malloc0(svb->sig_len);
>> + cpu_physical_memory_read(svb->sig_addr, svb_sig, svb->sig_len);
>> +
>> + if (gnutls_pkcs7_init(sig) < 0) {
>> + error_report("Failed to initalize pkcs7 data.");
>> + return -1;
>> + }
>> +
>> + datum_init(datum_sig, svb_sig, svb->sig_len);
>> + return gnutls_pkcs7_import(*sig, &datum_sig, GNUTLS_X509_FMT_DER);
>> +
>> +}
>> +#endif /* CONFIG_GNUTLS */
>> +
>> void handle_diag_508(CPUS390XState *env, uint64_t r1, uint64_t r3,
>> uintptr_t ra)
>> {
>> + S390IPLCertificateStore *qcs = s390_ipl_get_certificate_store();
>> + size_t csi_size = sizeof(Diag508CertificateStoreInfo);
>> uint64_t subcode = env->regs[r3];
>> + uint64_t addr = env->regs[r1];
>> int rc;
>>
>> if (env->psw.mask & PSW_MASK_PSTATE) {
>> @@ -506,7 +569,73 @@ 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:
>> + size_t svb_size = sizeof(Diag508SignatureVerificationBlock);
>> + Diag508SignatureVerificationBlock *svb;
>> +
>> + if (!qcs || !qcs->count) {
>> + error_report("No certificates in cert store.");
>
> Not sure whether we should print an error by default here ... it's likely
> better to use a trace_...() function here, I think.
>
The return value is likely sufficient enough, and the caller can decide
if it's necessary to print a message or handle it some other way.
>> + rc = DIAG_508_RC_NO_CERTS;
>> + break;
>> + }
>> +
>> + if (!diag_parm_addr_valid(addr, svb_size, false) ||
>> + !diag_parm_addr_valid(addr, csi_size, true)) {
>> + s390_program_interrupt(env, PGM_ADDRESSING, ra);
>> + return;
>> + }
>> +
>> + svb = g_new0(Diag508SignatureVerificationBlock, 1);
>> + cpu_physical_memory_read(addr, svb, svb_size);
>
> Do you need to byteswap the read values with be_to_cpuXX() here?
>
For cross-arch compliance, yeah... I'll fix that for next time.
>> +#ifdef CONFIG_GNUTLS
>> + gnutls_pkcs7_t sig = NULL;
>> + gnutls_datum_t comp;
>> + int i;
>> +
>> + if (diag_508_init_comp(&comp, svb) < 0) {
>> + rc = DIAG_508_RC_INVAL_COMP_DATA;
>> + g_free(svb);
>> + break;
>> + }
>> +
>> + if (diag_508_init_signature(&sig, svb) < 0) {
>> + rc = DIAG_508_RC_INVAL_PKCS7_SIG;
>> + gnutls_pkcs7_deinit(sig);
>> + g_free(svb);
>> + break;
>> + }
>> +
>> + rc = DIAG_508_RC_FAIL_VERIF;
>> + /*
>> + * It is uncertain which certificate contains
>> + * the analogous key to verify the signed data
>> + */
>> + for (i = 0; i < qcs->count; i++) {
>> + gnutls_x509_crt_t g_cert = NULL;
>> + if (g_init_cert((uint8_t *)qcs->certs[i].raw,
>> qcs->certs[i].size, &g_cert)) {
>> + continue;
>> + }
>> +
>> + if (gnutls_pkcs7_verify_direct(sig, g_cert, 0, &comp, 0) == 0) {
>> + svb->csi.idx = i;
>> + svb->csi.len = qcs->certs[i].size;
>> + cpu_physical_memory_write(addr, &svb->csi,
>> + be32_to_cpu(csi_size));
>> + rc = DIAG_508_RC_OK;
>> + break;
>> + }
>> +
>> + gnutls_x509_crt_deinit(g_cert);
>> + }
>> +
>> + gnutls_pkcs7_deinit(sig);
>> +#else
>> + rc = DIAG_508_RC_FAIL_VERIF;
>> +#endif /* CONFIG_GNUTLS */
>> + g_free(svb);
>> break;
>> default:
>> s390_program_interrupt(env, PGM_SPECIFICATION, ra);
>
> Thomas
>
>
--
Regards,
Collin
