On Wed, Feb 24, 2021 at 10:47:30AM +0200, Adrian Catangiu wrote: > This feature is aimed at virtualized or containerized environments > where VM or container snapshotting duplicates memory state, which is a > challenge for applications that want to generate unique data such as > request IDs, UUIDs, and cryptographic nonces. > > The patch set introduces a mechanism that provides a userspace > interface for applications and libraries to be made aware of uniqueness > breaking events such as VM or container snapshotting, and allow them to > react and adapt to such events. > > Solving the uniqueness problem strongly enough for cryptographic > purposes requires a mechanism which can deterministically reseed > userspace PRNGs with new entropy at restore time. This mechanism must > also support the high-throughput and low-latency use-cases that led > programmers to pick a userspace PRNG in the first place; be usable by > both application code and libraries; allow transparent retrofitting > behind existing popular PRNG interfaces without changing application > code; it must be efficient, especially on snapshot restore; and be > simple enough for wide adoption. > > The first patch in the set implements a device driver which exposes a > the /dev/sysgenid char device to userspace. Its associated filesystem > operations operations can be used to build a system level safe workflow > that guest software can follow to protect itself from negative system > snapshot effects. > > The second patch in the set adds a VmGenId driver which makes use of > the ACPI vmgenid device to drive SysGenId and to reseed kernel entropy > following VM snapshots. > > **Please note**, SysGenID alone does not guarantee complete snapshot > safety to applications using it. A certain workflow needs to be > followed at the system level, in order to make the system > snapshot-resilient. Please see the "Snapshot Safety Prerequisites" > section in the included SysGenID documentation. > > --- > > v6 -> v7: > - remove sysgenid uevent How about we drop mmap too? There's simply no way I can see to make it safe, and no implementation is worse than a racy one imho. Yea there's some decumentation explaining how it is not supposed to be used but it will *seem* to work for people and we will be stuck trying to maintain it. Let's see if userspace using this often enough to make the system call > v5 -> v6: > > - sysgenid: watcher tracking disabled by default > - sysgenid: add SYSGENID_SET_WATCHER_TRACKING ioctl to allow each > file descriptor to set whether they should be tracked as watchers > - rename SYSGENID_FORCE_GEN_UPDATE -> SYSGENID_TRIGGER_GEN_UPDATE > - rework all documentation to clearly capture all prerequisites for > achieving snapshot safety when using the provided mechanism > - sysgenid documentation: replace individual filesystem operations > examples with a higher level example showcasing system-level > snapshot-safe workflow > > v4 -> v5: > > - sysgenid: generation changes are also exported through uevents > - remove SYSGENID_GET_OUTDATED_WATCHERS ioctl > - document sysgenid ioctl major/minor numbers > > v3 -> v4: > > - split functionality in two separate kernel modules: > 1. drivers/misc/sysgenid.c which provides the generic userspace > interface and mechanisms > 2. drivers/virt/vmgenid.c as VMGENID acpi device driver that seeds > kernel entropy and acts as a driving backend for the generic > sysgenid > - rename /dev/vmgenid -> /dev/sysgenid > - rename uapi header file vmgenid.h -> sysgenid.h > - rename ioctls VMGENID_* -> SYSGENID_* > - add ‘min_gen’ parameter to SYSGENID_FORCE_GEN_UPDATE ioctl > - fix races in documentation examples > > v2 -> v3: > > - separate the core driver logic and interface, from the ACPI device. > The ACPI vmgenid device is now one possible backend > - fix issue when timeout=0 in VMGENID_WAIT_WATCHERS > - add locking to avoid races between fs ops handlers and hw irq > driven generation updates > - change VMGENID_WAIT_WATCHERS ioctl so if the current caller is > outdated or a generation change happens while waiting (thus making > current caller outdated), the ioctl returns -EINTR to signal the > user to handle event and retry. Fixes blocking on oneself > - add VMGENID_FORCE_GEN_UPDATE ioctl conditioned by > CAP_CHECKPOINT_RESTORE capability, through which software can force > generation bump > > v1 -> v2: > > - expose to userspace a monotonically increasing u32 Vm Gen Counter > instead of the hw VmGen UUID > - since the hw/hypervisor-provided 128-bit UUID is not public > anymore, add it to the kernel RNG as device randomness > - insert driver page containing Vm Gen Counter in the user vma in > the driver's mmap handler instead of using a fault handler > - turn driver into a misc device driver to auto-create /dev/vmgenid > - change ioctl arg to avoid leaking kernel structs to userspace > - update documentation > > Adrian Catangiu (2): > drivers/misc: sysgenid: add system generation id driver > drivers/virt: vmgenid: add vm generation id driver > > Documentation/misc-devices/sysgenid.rst | 229 +++++++++++++++ > Documentation/userspace-api/ioctl/ioctl-number.rst | 1 + > Documentation/virt/vmgenid.rst | 36 +++ > MAINTAINERS | 15 + > drivers/misc/Kconfig | 15 + > drivers/misc/Makefile | 1 + > drivers/misc/sysgenid.c | 322 +++++++++++++++++++++ > drivers/virt/Kconfig | 13 + > drivers/virt/Makefile | 1 + > drivers/virt/vmgenid.c | 153 ++++++++++ > include/uapi/linux/sysgenid.h | 18 ++ > 11 files changed, 804 insertions(+) > create mode 100644 Documentation/misc-devices/sysgenid.rst > create mode 100644 Documentation/virt/vmgenid.rst > create mode 100644 drivers/misc/sysgenid.c > create mode 100644 drivers/virt/vmgenid.c > create mode 100644 include/uapi/linux/sysgenid.h > > -- > 2.7.4 > > > > > Amazon Development Center (Romania) S.R.L. registered office: 27A Sf. Lazar Street, UBC5, floor 2, Iasi, Iasi County, 700045, Romania. Registered in Romania. Registration number J22/2621/2005.
