Hello,
On Mon, Jul 18, 2016 at 11:03:53AM +0100, Stefan Hajnoczi wrote:
> On Mon, Jul 18, 2016 at 01:37:40PM +0900, Namhyung Kim wrote:
> > From: Namhyung Kim <namhyung@xxxxxxxxx>
> >
> > Add virtio pstore device to allow kernel log files saved on the host.
> > It will save the log files on the directory given by pstore device
> > option.
> >
> > $ qemu-system-x86_64 -device virtio-pstore,directory=dir-xx ...
> >
> > (guest) # echo c > /proc/sysrq-trigger
> >
> > $ ls dir-xx
> > dmesg-0.enc.z dmesg-1.enc.z
> >
> > The log files are usually compressed using zlib. Users can see the log
> > messages directly on the host or on the guest (using pstore filesystem).
>
> The implementation is synchronous (i.e. can pause guest code execution),
> does not handle write errors, and does not limit the amount of data the
> guest can write. This is sufficient for ad-hoc debugging and usage with
> trusted guests.
>
> If you want this to be available in environments where the guest isn't
> trusted then there must be a limit on how much the guest can write or
> some kind of log rotation.
Right. The synchronous IO is required by the pstore subsystem
implementation AFAIK (it uses a single psinfo->buf in the loop). And
I agree that it should have a way to handle write errors and to limit
amount of data.
>
> >
> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > Cc: Radim Kr??m???? <rkrcmar@xxxxxxxxxx>
> > Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> > Cc: Anthony Liguori <aliguori@xxxxxxxxxx>
> > Cc: Anton Vorontsov <anton@xxxxxxxxxx>
> > Cc: Colin Cross <ccross@xxxxxxxxxxx>
> > Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> > Cc: Tony Luck <tony.luck@xxxxxxxxx>
> > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Minchan Kim <minchan@xxxxxxxxxx>
> > Cc: kvm@xxxxxxxxxxxxxxx
> > Cc: qemu-devel@xxxxxxxxxx
> > Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxx>
> > ---
[SNIP]
> > +
> > +static void virtio_pstore_to_filename(VirtIOPstore *s, char *buf, size_t sz,
> > + struct virtio_pstore_hdr *hdr)
> > +{
> > + const char *basename;
> > +
> > + switch (hdr->type) {
>
> Missing le16_to_cpu()?
>
> > + case VIRTIO_PSTORE_TYPE_DMESG:
> > + basename = "dmesg";
> > + break;
> > + default:
> > + basename = "unknown";
> > + break;
> > + }
> > +
> > + snprintf(buf, sz, "%s/%s-%llu%s", s->directory, basename,
> > + (unsigned long long) hdr->id,
>
> Missing le64_to_cpu()?
>
> > + hdr->flags & VIRTIO_PSTORE_FL_COMPRESSED ? ".enc.z" : "");
>
> Missing le32_to_cpu()?
Oops, will fix.
>
> > +}
> > +
> > +static void virtio_pstore_from_filename(VirtIOPstore *s, char *name,
> > + char *buf, size_t sz,
> > + struct virtio_pstore_hdr *hdr)
> > +{
> > + size_t len = strlen(name);
> > +
> > + hdr->flags = 0;
> > + if (!strncmp(name + len - 6, ".enc.z", 6)) {
>
> Please use g_str_has_suffix(name, ".enc.z") to avoid accessing before
> the beginning of the string if the filename is shorter than 6
> characters.
Ah, ok.
>
> > + hdr->flags |= VIRTIO_PSTORE_FL_COMPRESSED;
> > + }
> > +
> > + snprintf(buf, sz, "%s/%s", s->directory, name);
> > +
> > + if (!strncmp(name, "dmesg-", 6)) {
>
> g_str_has_prefix(name, "dmesg-")
>
> > + hdr->type = cpu_to_le16(VIRTIO_PSTORE_TYPE_DMESG);
> > + name += 6;
> > + } else if (!strncmp(name, "unknown-", 8)) {
>
> g_str_has_prefix(name, "unknown-")
Will change.
>
> > + hdr->type = cpu_to_le16(VIRTIO_PSTORE_TYPE_UNKNOWN);
> > + name += 8;
> > + }
> > +
> > + qemu_strtoull(name, NULL, 0, &hdr->id);
> > +}
> > +
> > +static ssize_t virtio_pstore_do_open(VirtIOPstore *s)
> > +{
> > + s->dir = opendir(s->directory);
> > + if (s->dir == NULL) {
> > + return -1;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static ssize_t virtio_pstore_do_read(VirtIOPstore *s, void *buf, size_t sz,
> > + struct virtio_pstore_hdr *hdr)
> > +{
> > + char path[PATH_MAX];
> > + FILE *fp;
> > + ssize_t len;
> > + struct stat stbuf;
> > + struct dirent *dent;
> > +
> > + if (s->dir == NULL) {
> > + return -1;
> > + }
> > +
> > + dent = readdir(s->dir);
> > + while (dent) {
> > + if (dent->d_name[0] != '.') {
> > + break;
> > + }
> > + dent = readdir(s->dir);
> > + }
> > +
> > + if (dent == NULL) {
> > + return 0;
> > + }
> > +
> > + virtio_pstore_from_filename(s, dent->d_name, path, sizeof(path), hdr);
> > + if (stat(path, &stbuf) < 0) {
> > + return -1;
> > + }
>
> Please use fstat(fileno(fp), &stbuf) after opening the file instead.
> The race condition doesn't matter in this case but the race-free code is
> just as simple so it's one less thing someone reading the code has to
> worry about.
Fair enough.
>
> > +
> > + fp = fopen(path, "r");
> > + if (fp == NULL) {
> > + error_report("cannot open %s (%p %p)", path, s, s->directory);
> > + return -1;
> > + }
> > +
> > + len = fread(buf, 1, sz, fp);
> > + if (len < 0 && errno == EAGAIN) {
> > + len = 0;
> > + }
> > +
> > + hdr->id = cpu_to_le64(hdr->id);
> > + hdr->flags = cpu_to_le32(hdr->flags);
> > + hdr->time_sec = cpu_to_le64(stbuf.st_ctim.tv_sec);
> > + hdr->time_nsec = cpu_to_le32(stbuf.st_ctim.tv_nsec);
> > +
> > + fclose(fp);
> > + return len;
> > +}
> > +
[SNIP]
> > +static void virtio_pstore_handle_io(VirtIODevice *vdev, VirtQueue *vq)
> > +{
> > + VirtIOPstore *s = VIRTIO_PSTORE(vdev);
> > + VirtQueueElement *elem;
> > + struct virtio_pstore_hdr *hdr;
> > + ssize_t len;
> > +
> > + for (;;) {
> > + elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
> > + if (!elem) {
> > + return;
> > + }
> > +
> > + hdr = elem->out_sg[0].iov_base;
> > + if (elem->out_sg[0].iov_len != sizeof(*hdr)) {
> > + error_report("invalid header size: %u",
> > + (unsigned)elem->out_sg[0].iov_len);
> > + exit(1);
> > + }
>
> Please use iov_to_buf() instead of directly accessing out_sg[]. Virtio
> devices are not supposed to assume a particular iovec layout. In other
> words, virtio_pstore_hdr could be split across multiple out_sg[] iovecs.
I got it.
>
> You must also copy in data (similar to Linux syscall implementations) to
> prevent the guest from modifying data while the command is processed.
> Such race conditions could lead to security bugs.
Ok, but this assumes the operation is synchronous. I agree on your
opinion if I could make it async.
>
> > +
> > + switch (hdr->cmd) {
> > + case VIRTIO_PSTORE_CMD_OPEN:
> > + len = virtio_pstore_do_open(s);
> > + break;
> > + case VIRTIO_PSTORE_CMD_READ:
> > + len = virtio_pstore_do_read(s, elem->in_sg[0].iov_base,
> > + elem->in_sg[0].iov_len, hdr);
>
> Same issue with iovec layout for in_sg[] here. The guest driver must be
> able to submit any in_sg[] iovec array and the device cannot assume
> in_sg[0] is the only iovec to fill.
Ok.
>
> > + break;
> > + case VIRTIO_PSTORE_CMD_WRITE:
> > + len = virtio_pstore_do_write(s, elem->out_sg[1].iov_base,
> > + elem->out_sg[1].iov_len, hdr);
> > + break;
> > + case VIRTIO_PSTORE_CMD_CLOSE:
> > + len = virtio_pstore_do_close(s);
> > + break;
> > + case VIRTIO_PSTORE_CMD_ERASE:
> > + len = virtio_pstore_do_erase(s, hdr);
> > + break;
> > + default:
> > + len = -1;
> > + break;
> > + }
> > +
> > + if (len < 0) {
> > + return;
> > + }
> > +
> > + virtqueue_push(vq, elem, len);
> > +
> > + virtio_notify(vdev, vq);
> > + g_free(elem);
> > + }
> > +}
> > +
> > +static void virtio_pstore_device_realize(DeviceState *dev, Error **errp)
> > +{
> > + VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> > + VirtIOPstore *s = VIRTIO_PSTORE(dev);
> > +
> > + virtio_init(vdev, "virtio-pstore", VIRTIO_ID_PSTORE, 0);
> > +
> > + s->vq = virtio_add_queue(vdev, 128, virtio_pstore_handle_io);
> > +}
> > +
> > +static void virtio_pstore_device_unrealize(DeviceState *dev, Error **errp)
> > +{
> > + VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> > +
> > + virtio_cleanup(vdev);
> > +}
> > +
> > +static uint64_t get_features(VirtIODevice *vdev, uint64_t f, Error **errp)
> > +{
> > + return f;
> > +}
> > +
> > +static void pstore_get_directory(Object *obj, Visitor *v,
> > + const char *name, void *opaque,
> > + Error **errp)
> > +{
> > + VirtIOPstore *s = opaque;
> > +
> > + visit_type_str(v, name, &s->directory, errp);
> > +}
> > +
> > +static void pstore_set_directory(Object *obj, Visitor *v,
> > + const char *name, void *opaque,
> > + Error **errp)
> > +{
> > + VirtIOPstore *s = opaque;
> > + Error *local_err = NULL;
> > + char *value;
> > +
> > + visit_type_str(v, name, &value, &local_err);
> > + if (local_err) {
> > + error_propagate(errp, local_err);
> > + return;
> > + }
> > +
> > + g_free(s->directory);
> > + s->directory = strdup(value);
>
> Please use g_strdup() since this is paired with g_free().
>
> Or even simpler would be s->directory = value and do not g_free(value)
> below.
Ok, I was not sure whether I could use it without alloc/free pair.
Will do it simpler way then. :)
>
> > +
> > + g_free(value);
> > +}
> > +
> > +static void pstore_release_directory(Object *obj, const char *name,
> > + void *opaque)
> > +{
> > + VirtIOPstore *s = opaque;
> > +
> > + g_free(s->directory);
> > + s->directory = NULL;
> > +}
> > +
> > +static Property virtio_pstore_properties[] = {
> > + DEFINE_PROP_END_OF_LIST(),
> > +};
> > +
> > +static void virtio_pstore_instance_init(Object *obj)
> > +{
> > + VirtIOPstore *s = VIRTIO_PSTORE(obj);
> > +
> > + object_property_add(obj, "directory", "str",
> > + pstore_get_directory, pstore_set_directory,
> > + pstore_release_directory, s, NULL);
> > +}
> > +
> > +static void virtio_pstore_class_init(ObjectClass *klass, void *data)
> > +{
> > + DeviceClass *dc = DEVICE_CLASS(klass);
> > + VirtioDeviceClass *vdc = VIRTIO_DEVICE_CLASS(klass);
> > +
> > + dc->props = virtio_pstore_properties;
> > + set_bit(DEVICE_CATEGORY_MISC, dc->categories);
> > + vdc->realize = virtio_pstore_device_realize;
> > + vdc->unrealize = virtio_pstore_device_unrealize;
> > + vdc->get_features = get_features;
> > +}
> > +
> > +static const TypeInfo virtio_pstore_info = {
> > + .name = TYPE_VIRTIO_PSTORE,
> > + .parent = TYPE_VIRTIO_DEVICE,
> > + .instance_size = sizeof(VirtIOPstore),
> > + .instance_init = virtio_pstore_instance_init,
> > + .class_init = virtio_pstore_class_init,
> > +};
> > +
> > +static void virtio_register_types(void)
> > +{
> > + type_register_static(&virtio_pstore_info);
> > +}
> > +
> > +type_init(virtio_register_types)
> > diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
> > index 9ed1624..5689c6f 100644
> > --- a/include/hw/pci/pci.h
> > +++ b/include/hw/pci/pci.h
> > @@ -79,6 +79,7 @@
> > #define PCI_DEVICE_ID_VIRTIO_SCSI 0x1004
> > #define PCI_DEVICE_ID_VIRTIO_RNG 0x1005
> > #define PCI_DEVICE_ID_VIRTIO_9P 0x1009
> > +#define PCI_DEVICE_ID_VIRTIO_PSTORE 0x100a
> >
> > #define PCI_VENDOR_ID_REDHAT 0x1b36
> > #define PCI_DEVICE_ID_REDHAT_BRIDGE 0x0001
> > diff --git a/include/hw/virtio/virtio-pstore.h b/include/hw/virtio/virtio-pstore.h
> > new file mode 100644
> > index 0000000..74cd1f6
> > --- /dev/null
> > +++ b/include/hw/virtio/virtio-pstore.h
> > @@ -0,0 +1,30 @@
> > +/*
> > + * Virtio Pstore Support
> > + *
> > + * Authors:
> > + * Namhyung Kim <namhyung@xxxxxxxxx>
> > + *
> > + * This work is licensed under the terms of the GNU GPL, version 2. See
> > + * the COPYING file in the top-level directory.
> > + *
> > + */
> > +
> > +#ifndef _QEMU_VIRTIO_PSTORE_H
> > +#define _QEMU_VIRTIO_PSTORE_H
> > +
> > +#include "standard-headers/linux/virtio_pstore.h"
> > +#include "hw/virtio/virtio.h"
> > +#include "hw/pci/pci.h"
> > +
> > +#define TYPE_VIRTIO_PSTORE "virtio-pstore-device"
> > +#define VIRTIO_PSTORE(obj) \
> > + OBJECT_CHECK(VirtIOPstore, (obj), TYPE_VIRTIO_PSTORE)
> > +
> > +typedef struct VirtIOPstore {
> > + VirtIODevice parent_obj;
> > + VirtQueue *vq;
> > + char *directory;
> > + DIR *dir;
> > +} VirtIOPstore;
> > +
> > +#endif
> > diff --git a/include/standard-headers/linux/virtio_ids.h b/include/standard-headers/linux/virtio_ids.h
> > index 77925f5..cba6322 100644
> > --- a/include/standard-headers/linux/virtio_ids.h
> > +++ b/include/standard-headers/linux/virtio_ids.h
> > @@ -41,5 +41,6 @@
> > #define VIRTIO_ID_CAIF 12 /* Virtio caif */
> > #define VIRTIO_ID_GPU 16 /* virtio GPU */
> > #define VIRTIO_ID_INPUT 18 /* virtio input */
> > +#define VIRTIO_ID_PSTORE 19 /* virtio pstore */
>
> 19 has already been reserved. 22 is the next free ID (vsock, crypto,
> and sdm are currently under review and already use 19, 20, and 21).
I wasn't aware of the ongoing works but Cornelia already told me about
it. Will update.
>
> Please send a VIRTIO draft specification to
> virtio-dev@xxxxxxxxxxxxxxxxxxxx. You can find information on the VIRTIO
> standards process here:
> https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio
Thank you very much for this information and your detailed review!
I'll take a look at the virtio standards process too.
Thanks,
Namhyung
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