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[libvirt] [RFC PATCH v2] qemu: Add suport for pci-assign.configfd option



This allows libvirt to open the PCI device sysfs config file prior
to dropping privileges so qemu can access the full config space.
Without this, a de-privileged qemu can only access the first 64
bytes of config space.

Signed-off-by: Alex Williamson <alex williamson redhat com>
---

v2:
 - fix qemuargs, two separate args (thanks Chris)
 - don't hardcode pci segment
 - error message of open() fail

 src/qemu/qemu_conf.c   |   89 +++++++++++++++++++++++++++++++++++++++++++++++-
 src/qemu/qemu_conf.h   |    8 ++++
 src/qemu/qemu_driver.c |    2 +
 3 files changed, 95 insertions(+), 4 deletions(-)

diff --git a/src/qemu/qemu_conf.c b/src/qemu/qemu_conf.c
index d7bc798..24c360e 100644
--- a/src/qemu/qemu_conf.c
+++ b/src/qemu/qemu_conf.c
@@ -1345,6 +1345,48 @@ fail:
     return -1;
 }
 
+void qemudParsePCIDeviceStrs(const char *qemu, unsigned long long *flags)
+{
+    const char *const qemuarg[] = { qemu, "-device", "pci-assign,?", NULL };
+    const char *const qemuenv[] = { "LC_ALL=C", NULL };
+    pid_t child;
+    int status;
+    int newstderr = -1;
+
+    if (virExec(qemuarg, qemuenv, NULL,
+                &child, -1, NULL, &newstderr, VIR_EXEC_CLEAR_CAPS) < 0)
+        return;
+
+    char *pciassign = NULL;
+    enum { MAX_PCI_OUTPUT_SIZE = 1024*4 };
+    int len = virFileReadLimFD(newstderr, MAX_PCI_OUTPUT_SIZE, &pciassign);
+    if (len < 0) {
+        virReportSystemError(errno,
+                             _("Unable to read %s pci-assign device output"),
+                             qemu);
+        goto cleanup;
+    }
+
+    if (strstr(pciassign, "pci-assign.configfd"))
+        *flags |= QEMUD_CMD_FLAG_PCI_CONFIGFD;
+
+cleanup:
+    VIR_FREE(pciassign);
+    close(newstderr);
+rewait:
+    if (waitpid(child, &status, 0) != child) {
+        if (errno == EINTR)
+            goto rewait;
+
+        VIR_ERROR(_("Unexpected exit status from qemu %d pid %lu"),
+                  WEXITSTATUS(status), (unsigned long)child);
+    }
+    if (WEXITSTATUS(status) != 0) {
+        VIR_WARN("Unexpected exit status '%d', qemu probably failed",
+                 WEXITSTATUS(status));
+    }
+}
+
 int qemudExtractVersionInfo(const char *qemu,
                             unsigned int *retversion,
                             unsigned long long *retflags) {
@@ -1378,6 +1420,9 @@ int qemudExtractVersionInfo(const char *qemu,
                           &version, &is_kvm, &kvm_version) == -1)
         goto cleanup2;
 
+    if (flags & QEMUD_CMD_FLAG_DEVICE)
+        qemudParsePCIDeviceStrs(qemu, &flags);
+
     if (retversion)
         *retversion = version;
     if (retflags)
@@ -2887,8 +2932,33 @@ error:
 }
 
 
+int
+qemudOpenPCIConfig(virDomainHostdevDefPtr dev)
+{
+    char *path = NULL;
+    int configfd = -1;
+
+    if (virAsprintf(&path, "/sys/bus/pci/devices/%04x:%02x:%02x.%01x/config",
+                    dev->source.subsys.u.pci.domain,
+                    dev->source.subsys.u.pci.bus,
+                    dev->source.subsys.u.pci.slot,
+                    dev->source.subsys.u.pci.function) < 0) {
+        virReportOOMError();
+        return -1;
+    }
+
+    configfd = open(path, O_RDWR, 0);
+
+    if (configfd < 0)
+        virReportSystemError(errno, _("Failed opening %s"), path);
+
+    VIR_FREE(path);
+
+    return configfd;
+}
+
 char *
-qemuBuildPCIHostdevDevStr(virDomainHostdevDefPtr dev)
+qemuBuildPCIHostdevDevStr(virDomainHostdevDefPtr dev, int configfd)
 {
     virBuffer buf = VIR_BUFFER_INITIALIZER;
 
@@ -2898,6 +2968,8 @@ qemuBuildPCIHostdevDevStr(virDomainHostdevDefPtr dev)
                       dev->source.subsys.u.pci.slot,
                       dev->source.subsys.u.pci.function);
     virBufferVSprintf(&buf, ",id=%s", dev->info.alias);
+    if (configfd >= 0)
+        virBufferVSprintf(&buf, ",configfd=%d", configfd);
     if (qemuBuildDeviceAddressStr(&buf, &dev->info) < 0)
         goto error;
 
@@ -4600,8 +4672,21 @@ int qemudBuildCommandLine(virConnectPtr conn,
         if (hostdev->mode == VIR_DOMAIN_HOSTDEV_MODE_SUBSYS &&
             hostdev->source.subsys.type == VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_PCI) {
             if (qemuCmdFlags & QEMUD_CMD_FLAG_DEVICE) {
+                int configfd = -1;
+                if (qemuCmdFlags & QEMUD_CMD_FLAG_PCI_CONFIGFD) {
+                    configfd = qemudOpenPCIConfig(hostdev);
+
+                    if (configfd >= 0) {
+                        if (VIR_REALLOC_N(*vmfds, (*nvmfds)+1) < 0) {
+                            close(configfd);
+                            goto no_memory;
+                        }
+
+                        (*vmfds)[(*nvmfds)++] = configfd;
+                    }
+                }
                 ADD_ARG_LIT("-device");
-                if (!(devstr = qemuBuildPCIHostdevDevStr(hostdev)))
+                if (!(devstr = qemuBuildPCIHostdevDevStr(hostdev, configfd)))
                     goto error;
                 ADD_ARG(devstr);
             } else if (qemuCmdFlags & QEMUD_CMD_FLAG_PCIDEVICE) {
diff --git a/src/qemu/qemu_conf.h b/src/qemu/qemu_conf.h
index a101e47..64fab60 100644
--- a/src/qemu/qemu_conf.h
+++ b/src/qemu/qemu_conf.h
@@ -88,6 +88,7 @@ enum qemud_cmd_flags {
     QEMUD_CMD_FLAG_NO_HPET       = (1LL << 33), /* -no-hpet flag is supported */
     QEMUD_CMD_FLAG_NO_KVM_PIT    = (1LL << 34), /* -no-kvm-pit-reinjection supported */
     QEMUD_CMD_FLAG_TDF           = (1LL << 35), /* -tdf flag (user-mode pit catchup) */
+    QEMUD_CMD_FLAG_PCI_CONFIGFD  = (1LL << 36), /* pci-assign.configfd */
 };
 
 /* Main driver state */
@@ -190,6 +191,9 @@ int         qemudParseHelpStr           (const char *qemu,
                                          unsigned int *is_kvm,
                                          unsigned int *kvm_version);
 
+void        qemudParsePCIDeviceStrs     (const char *qemu,
+                                         unsigned long long *qemuCmdFlags);
+
 int         qemudBuildCommandLine       (virConnectPtr conn,
                                          struct qemud_driver *driver,
                                          virDomainDefPtr def,
@@ -242,7 +246,9 @@ char * qemuBuildSoundDevStr(virDomainSoundDefPtr sound);
 /* Legacy, pre device support */
 char * qemuBuildPCIHostdevPCIDevStr(virDomainHostdevDefPtr dev);
 /* Current, best practice */
-char * qemuBuildPCIHostdevDevStr(virDomainHostdevDefPtr dev);
+char * qemuBuildPCIHostdevDevStr(virDomainHostdevDefPtr dev, int configfd);
+
+int qemudOpenPCIConfig(virDomainHostdevDefPtr dev);
 
 /* Current, best practice */
 char * qemuBuildChrChardevStr(virDomainChrDefPtr dev);
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index dd5bd24..219a973 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -7567,7 +7567,7 @@ static int qemudDomainAttachHostPciDevice(struct qemud_driver *driver,
         if (qemuDomainPCIAddressEnsureAddr(priv->pciaddrs, &hostdev->info) < 0)
             goto error;
 
-        if (!(devstr = qemuBuildPCIHostdevDevStr(hostdev)))
+        if (!(devstr = qemuBuildPCIHostdevDevStr(hostdev, -1)))
             goto error;
     }
 


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