[Qemu-devel] [PATCH v3 1/1] hw/scsi: support SCSI-2 passthrough without PI

[Daniel Henrique Barboza]

QEMU SCSI code makes assumptions about how the PROTECT and BYTCHK
works in the protocol, denying support for PI (Protection
Information) in case the guest OS requests it. However, in SCSI versions 2
and older, there is no PI concept in the protocol.

This means that when dealing with such devices:

- there is no PROTECT bit in byte 5 of the standard INQUIRY response. The
whole byte is marked as "Reserved";

- there is no RDPROTECT in byte 2 of READ. We have 'Logical Unit Number'
in this field instead;

- there is no VRPROTECT in byte 2 of VERIFY. We have 'Logical Unit Number'
in this field instead. This also means that the BYTCHK bit in this case
is not related to PI.

Since QEMU does not consider these changes, a SCSI passthrough using
a SCSI-2 device will not work. It will mistake these fields with
PI information and return Illegal Request SCSI SENSE thinking
that the driver is asking for PI support.

This patch fixes it by adding a new attribute called 'scsi_version'
that is read from the standard INQUIRY response of passthrough
devices. This allows for a version verification before applying
conditions related to PI that doesn't apply for older versions.

Reported-by: Dac Nguyen <address@hidden>
Signed-off-by: Daniel Henrique Barboza <address@hidden>
---

Changes in v3:
- moved the scsi_version initialization from realize functions to
reset functions, allowing the scsi_version to be redefined again after
each reboot.


 hw/scsi/scsi-disk.c    | 14 +++++++++++---
 hw/scsi/scsi-generic.c | 46 +++++++++++++++++++++++++++++++++++-----------
 include/hw/scsi/scsi.h |  1 +
 3 files changed, 47 insertions(+), 14 deletions(-)

diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index f5ab767ab5..115fbd1e8f 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -2191,7 +2191,7 @@ static int32_t scsi_disk_dma_command(SCSIRequest *req, 
uint8_t *buf)
     case READ_12:
     case READ_16:
         DPRINTF("Read (sector %" PRId64 ", count %u)\n", r->req.cmd.lba, len);
-        if (r->req.cmd.buf[1] & 0xe0) {
+        if ((r->req.cmd.buf[1] & 0xe0) && (s->qdev.scsi_version > 2)) {
             goto illegal_request;
         }
         if (!check_lba_range(s, r->req.cmd.lba, len)) {
@@ -2221,8 +2221,12 @@ static int32_t scsi_disk_dma_command(SCSIRequest *req, 
uint8_t *buf)
         /* We get here only for BYTCHK == 0x01 and only for scsi-block.
          * As far as DMA is concerned, we can treat it the same as a write;
          * scsi_block_do_sgio will send VERIFY commands.
+         *
+         * For scsi versions 2 and older, the BYTCHK isn't related
+         * to VRPROTECT (in fact, there is no VRPROTECT). Skip
+         * this check in these versions.
          */
-        if (r->req.cmd.buf[1] & 0xe0) {
+        if ((r->req.cmd.buf[1] & 0xe0) && (s->qdev.scsi_version > 2)) {
             goto illegal_request;
         }
         if (!check_lba_range(s, r->req.cmd.lba, len)) {
@@ -2268,6 +2272,8 @@ static void scsi_disk_reset(DeviceState *dev)
     /* reset tray statuses */
     s->tray_locked = 0;
     s->tray_open = 0;
+
+    s->qdev.scsi_version = -1;
 }
 
 static void scsi_disk_resize_cb(void *opaque)
@@ -2812,6 +2818,8 @@ static bool scsi_block_is_passthrough(SCSIDiskState *s, 
uint8_t *buf)
 static int32_t scsi_block_dma_command(SCSIRequest *req, uint8_t *buf)
 {
     SCSIBlockReq *r = (SCSIBlockReq *)req;
+    SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, req->dev);
+
     r->cmd = req->cmd.buf[0];
     switch (r->cmd >> 5) {
     case 0:
@@ -2837,7 +2845,7 @@ static int32_t scsi_block_dma_command(SCSIRequest *req, 
uint8_t *buf)
         abort();
     }
 
-    if (r->cdb1 & 0xe0) {
+    if ((r->cdb1 & 0xe0) && (s->qdev.scsi_version > 2)) {
         /* Protection information is not supported.  */
         scsi_check_condition(&r->req, SENSE_CODE(INVALID_FIELD));
         return 0;
diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
index 4753f8738f..3b34f167c7 100644
--- a/hw/scsi/scsi-generic.c
+++ b/hw/scsi/scsi-generic.c
@@ -194,17 +194,40 @@ static void scsi_read_complete(void * opaque, int ret)
             r->buf[3] |= 0x80;
         }
     }
-    if (s->type == TYPE_DISK &&
-        r->req.cmd.buf[0] == INQUIRY &&
-        r->req.cmd.buf[2] == 0xb0) {
-        uint32_t max_transfer =
-            blk_get_max_transfer(s->conf.blk) / s->blocksize;
-
-        assert(max_transfer);
-        stl_be_p(&r->buf[8], max_transfer);
-        /* Also take care of the opt xfer len. */
-        stl_be_p(&r->buf[12],
-                 MIN_NON_ZERO(max_transfer, ldl_be_p(&r->buf[12])));
+    if (r->req.cmd.buf[0] == INQUIRY) {
+        /*
+         *  EVPD set to zero returns the standard INQUIRY data.
+         *
+         *  Check if scsi_version is unset (-1) to avoid re-defining it
+         *  each time an INQUIRY with standard data is received.
+         *  scsi_version is initialized with -1 in scsi_generic_reset
+         *  and scsi_disk_reset, making sure that we'll set the
+         *  scsi_version after a reset. If the version field of the
+         *  INQUIRY response somehow changes after a guest reboot,
+         *  we'll be able to keep track of it.
+         *
+         *  On SCSI-2 and older, first 3 bits of byte 2 is the
+         *  ANSI-approved version, while on later versions the
+         *  whole byte 2 contains the version. Check if we're dealing
+         *  with a newer version and, in that case, assign the
+         *  whole byte.
+         */
+        if ((s->scsi_version == -1) && ((r->req.cmd.buf[1] & 0x01) == 0)) {
+            s->scsi_version = r->buf[2] & 0x07;
+            if (s->scsi_version > 2) {
+                s->scsi_version = r->buf[2];
+            }
+        }
+        if (s->type == TYPE_DISK && r->req.cmd.buf[2] == 0xb0) {
+            uint32_t max_transfer =
+                blk_get_max_transfer(s->conf.blk) / s->blocksize;
+
+            assert(max_transfer);
+            stl_be_p(&r->buf[8], max_transfer);
+            /* Also take care of the opt xfer len. */
+            stl_be_p(&r->buf[12],
+                     MIN_NON_ZERO(max_transfer, ldl_be_p(&r->buf[12])));
+        }
     }
     scsi_req_data(&r->req, len);
     scsi_req_unref(&r->req);
@@ -474,6 +497,7 @@ static void scsi_generic_reset(DeviceState *dev)
 {
     SCSIDevice *s = SCSI_DEVICE(dev);
 
+    s->scsi_version = -1;
     scsi_device_purge_requests(s, SENSE_CODE(RESET));
 }
 
diff --git a/include/hw/scsi/scsi.h b/include/hw/scsi/scsi.h
index 7ecaddac9d..a698c7f60c 100644
--- a/include/hw/scsi/scsi.h
+++ b/include/hw/scsi/scsi.h
@@ -85,6 +85,7 @@ struct SCSIDevice
     uint64_t max_lba;
     uint64_t wwn;
     uint64_t port_wwn;
+    int scsi_version;
 };
 
 extern const VMStateDescription vmstate_scsi_device;
-- 
2.14.3