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[src/trunk]: src/sys/dev/ic dev/ic/tpm: Take advantage of entropy source if a...



details:   https://anonhg.NetBSD.org/src/rev/df2c9353c6ca
branches:  trunk
changeset: 979655:df2c9353c6ca
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Jan 04 18:26:59 2021 +0000

description:
dev/ic/tpm: Take advantage of entropy source if available.

If the tpm is deactivated, though, detach the entropy source so we
don't continue to try polling it -- it can't be activated without a
reboot anyway.

diffstat:

 sys/dev/ic/tpm.c    |  188 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 sys/dev/ic/tpmreg.h |   22 +++++-
 sys/dev/ic/tpmvar.h |    9 ++-
 3 files changed, 215 insertions(+), 4 deletions(-)

diffs (291 lines):

diff -r e39767f21191 -r df2c9353c6ca sys/dev/ic/tpm.c
--- a/sys/dev/ic/tpm.c  Mon Jan 04 18:26:08 2021 +0000
+++ b/sys/dev/ic/tpm.c  Mon Jan 04 18:26:59 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: tpm.c,v 1.18 2021/01/04 18:26:08 riastradh Exp $       */
+/*     $NetBSD: tpm.c,v 1.19 2021/01/04 18:26:59 riastradh Exp $       */
 
 /*
  * Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -48,11 +48,12 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: tpm.c,v 1.18 2021/01/04 18:26:08 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: tpm.c,v 1.19 2021/01/04 18:26:59 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/types.h>
 
+#include <sys/atomic.h>
 #include <sys/bus.h>
 #include <sys/conf.h>
 #include <sys/device.h>
@@ -61,6 +62,7 @@
 #include <sys/pmf.h>
 #include <sys/proc.h>
 #include <sys/systm.h>
+#include <sys/workqueue.h>
 
 #include <dev/ic/tpmreg.h>
 #include <dev/ic/tpmvar.h>
@@ -325,6 +327,179 @@
        return 0;
 }
 
+static void
+tpm_tis12_rng_work(struct work *wk, void *cookie)
+{
+       struct tpm_softc *sc = cookie;
+       /*
+        * TPM Specification Version 1.2, Main Part 3: Commands,
+        * Sec. 13.6 TPM_GetRandom
+        */
+       struct {
+               struct tpm_header hdr;
+               uint32_t bytesRequested;
+       } __packed command;
+       struct response {
+               struct tpm_header hdr;
+               uint32_t randomBytesSize;
+               uint8_t bytes[64];
+       } __packed response;
+       bool busy, endwrite = false, endread = false;
+       size_t nread;
+       uint16_t tag;
+       uint32_t pktlen, code, nbytes;
+       int rv;
+
+       /* Acknowledge the request.  */
+       sc->sc_rndpending = 0;
+
+       /* Lock userland out of the tpm, or fail if it's already open.  */
+       mutex_enter(&sc->sc_lock);
+       busy = sc->sc_busy;
+       sc->sc_busy = true;
+       mutex_exit(&sc->sc_lock);
+       if (busy) {             /* tough */
+               aprint_debug_dev(sc->sc_dev, "%s: device in use\n", __func__);
+               return;
+       }
+
+       /* Encode the command.  */
+       memset(&command, 0, sizeof(command));
+       command.hdr.tag = htobe16(TPM_TAG_RQU_COMMAND);
+       command.hdr.length = htobe32(sizeof(command));
+       command.hdr.code = htobe32(TPM_ORD_GetRandom);
+       command.bytesRequested = htobe32(sizeof(response.bytes));
+
+       /* Write the command.   */
+       if ((rv = (*sc->sc_intf->start)(sc, UIO_WRITE)) != 0) {
+               device_printf(sc->sc_dev, "start write failed, error=%d\n",
+                   rv);
+               goto out;
+       }
+       endwrite = true;
+       if ((rv = (*sc->sc_intf->write)(sc, &command, sizeof(command))) != 0) {
+               device_printf(sc->sc_dev, "write failed, error=%d\n", rv);
+               goto out;
+       }
+       rv = (*sc->sc_intf->end)(sc, UIO_WRITE, 0);
+       endwrite = false;
+       if (rv) {
+               device_printf(sc->sc_dev, "end write failed, error=%d\n", rv);
+               goto out;
+       }
+
+       /* Read the response header.  */
+       if ((rv = (*sc->sc_intf->start)(sc, UIO_READ)) != 0) {
+               device_printf(sc->sc_dev, "start write failed, error=%d\n",
+                   rv);
+               goto out;
+       }
+       endread = true;
+       if ((rv = (*sc->sc_intf->read)(sc, &response.hdr, sizeof(response.hdr),
+                   &nread, 0)) != 0) {
+               device_printf(sc->sc_dev, "read failed, error=%d\n", rv);
+               goto out;
+       }
+
+       /* Verify the response header looks sensible.  */
+       if (nread != sizeof(response.hdr)) {
+               device_printf(sc->sc_dev, "read %zu bytes, expected %zu",
+                   nread, sizeof(response.hdr));
+               goto out;
+       }
+       tag = be16toh(response.hdr.tag);
+       pktlen = be32toh(response.hdr.length);
+       code = be32toh(response.hdr.code);
+       if (tag != TPM_TAG_RSP_COMMAND ||
+           pktlen < offsetof(struct response, bytes) ||
+           pktlen > sizeof(response) ||
+           code != 0) {
+               /*
+                * If the tpm itself is busy (e.g., it has yet to run a
+                * self-test, or it's in a timeout period to defend
+                * against brute force attacks), then we can try again
+                * later.  Otherwise, give up.
+                */
+               if (code & TPM_NON_FATAL) {
+                       aprint_debug_dev(sc->sc_dev, "%s: tpm busy, code=%u\n",
+                           __func__, code & ~TPM_NON_FATAL);
+                       rv = 0;
+               } else if (code == TPM_DEACTIVATED) {
+                       device_printf(sc->sc_dev, "tpm is deactivated\n");
+                       rv = ENXIO;
+               } else {
+                       device_printf(sc->sc_dev, "bad tpm response:"
+                           " tag=%u len=%u code=%u\n", tag, pktlen, code);
+                       hexdump(aprint_debug, "tpm response header",
+                           (const void *)&response.hdr,
+                           sizeof(response.hdr));
+                       rv = EIO;
+               }
+               goto out;
+       }
+
+       /* Read the response payload.  */
+       if ((rv = (*sc->sc_intf->read)(sc,
+                   (char *)&response + nread, pktlen - nread,
+                   NULL, TPM_PARAM_SIZE)) != 0) {
+               device_printf(sc->sc_dev, "read failed, error=%d\n", rv);
+               goto out;
+       }
+       endread = false;
+       if ((rv = (*sc->sc_intf->end)(sc, UIO_READ, 0)) != 0) {
+               device_printf(sc->sc_dev, "end read failed, error=%d\n", rv);
+               goto out;
+       }
+
+       /* Verify the number of bytes read looks sensible.  */
+       nbytes = be32toh(response.randomBytesSize);
+       if (nbytes > pktlen - offsetof(struct response, bytes)) {
+               device_printf(sc->sc_dev, "overlong GetRandom length:"
+                   " %u, max %zu\n",
+                   nbytes, pktlen - offsetof(struct response, bytes));
+               nbytes = pktlen - offsetof(struct response, bytes);
+       }
+
+       /*
+        * Enter the data into the entropy pool.  Conservatively (or,
+        * perhaps, cargocultily) estimate half a bit of entropy per
+        * bit of data.
+        */
+       rnd_add_data(&sc->sc_rnd, response.bytes, nbytes, (NBBY/2)*nbytes);
+
+out:   /*
+        * If the tpm is busted, no sense in trying again -- most
+        * likely, it is deactivated, and by the spec it cannot be
+        * reactivated until after a reboot.
+        */
+       if (rv) {
+               device_printf(sc->sc_dev, "deactivating entropy source\n");
+               rnd_detach_source(&sc->sc_rnd);
+               /* XXX worker thread can't workqueue_destroy its own queue */
+       }
+
+       /* End the read or write if still ongoing.  */
+       if (endread)
+               rv = (*sc->sc_intf->end)(sc, UIO_READ, rv);
+       if (endwrite)
+               rv = (*sc->sc_intf->end)(sc, UIO_WRITE, rv);
+
+       /* Relinquish the tpm back to userland.  */
+       mutex_enter(&sc->sc_lock);
+       KASSERT(sc->sc_busy);
+       sc->sc_busy = false;
+       mutex_exit(&sc->sc_lock);
+}
+
+static void
+tpm_tis12_rng_get(size_t nbytes, void *cookie)
+{
+       struct tpm_softc *sc = cookie;
+
+       if (atomic_swap_uint(&sc->sc_rndpending, 1) == 0)
+               workqueue_enqueue(sc->sc_rndwq, &sc->sc_rndwk, NULL);
+}
+
 static int
 tpm_tis12_init(struct tpm_softc *sc)
 {
@@ -347,6 +522,15 @@
        /* Abort whatever it thought it was doing. */
        bus_space_write_1(sc->sc_bt, sc->sc_bh, TPM_STS, TPM_STS_CMD_READY);
 
+       /* XXX Run this at higher priority?  */
+       if ((rv = workqueue_create(&sc->sc_rndwq, device_xname(sc->sc_dev),
+                   tpm_tis12_rng_work, sc, PRI_NONE, IPL_VM, WQ_MPSAFE)) != 0)
+               return rv;
+       rndsource_setcb(&sc->sc_rnd, tpm_tis12_rng_get, sc);
+       rnd_attach_source(&sc->sc_rnd, device_xname(sc->sc_dev),
+           RND_TYPE_RNG,
+           RND_FLAG_COLLECT_VALUE|RND_FLAG_ESTIMATE_VALUE|RND_FLAG_HASCB);
+
        return 0;
 }
 
diff -r e39767f21191 -r df2c9353c6ca sys/dev/ic/tpmreg.h
--- a/sys/dev/ic/tpmreg.h       Mon Jan 04 18:26:08 2021 +0000
+++ b/sys/dev/ic/tpmreg.h       Mon Jan 04 18:26:59 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: tpmreg.h,v 1.7 2021/01/04 18:22:19 riastradh Exp $     */
+/*     $NetBSD: tpmreg.h,v 1.8 2021/01/04 18:26:59 riastradh Exp $     */
 
 /*
  * Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -114,4 +114,24 @@
  */
 #define        TPM_SPACE_SIZE  0x5000
 
+#define        TPM_TAG_RQU_COMMAND             0x00c1
+#define        TPM_TAG_RSP_COMMAND             0x00c4
+
+#define        TPM_ORD_GetRandom               0x00000046
+
+/* TPM_RESULT return codes */
+#define        TPM_AUTHFAIL                    1
+#define        TPM_BADINDEX                    2
+#define        TPM_BAD_PARAMETER               3
+#define        TPM_AUDITFAILURE                4
+#define        TPM_CLEAR_DISABLED              5
+#define        TPM_DEACTIVATED                 6
+#define        TPM_DISABLED                    7
+#define        TPM_DISABLED_CMD                8
+#define        TPM_FAIL                        9
+#define        TPM_BAD_ORDINAL                 10
+/* ... */
+
+#define        TPM_NON_FATAL                   0x800
+
 #endif /* DEV_IC_TPMREG_H */
diff -r e39767f21191 -r df2c9353c6ca sys/dev/ic/tpmvar.h
--- a/sys/dev/ic/tpmvar.h       Mon Jan 04 18:26:08 2021 +0000
+++ b/sys/dev/ic/tpmvar.h       Mon Jan 04 18:26:59 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: tpmvar.h,v 1.8 2021/01/04 18:22:19 riastradh Exp $     */
+/*     $NetBSD: tpmvar.h,v 1.9 2021/01/04 18:26:59 riastradh Exp $     */
 
 /*
  * Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -62,6 +62,8 @@
 #include <sys/bus.h>
 #include <sys/device_if.h>
 #include <sys/mutex.h>
+#include <sys/rndsource.h>
+#include <sys/workqueue.h>
 
 struct tpm_softc;
 
@@ -91,6 +93,11 @@
        uint32_t sc_rev;
        uint32_t sc_status;
        uint32_t sc_caps;
+
+       struct krndsource sc_rnd;
+       struct workqueue *sc_rndwq;
+       struct work sc_rndwk;
+       volatile unsigned sc_rndpending;
 };
 
 bool tpm_suspend(device_t, const pmf_qual_t *);



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