On Tue, Jan 12, 2021 at 02:15:58PM +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 > read-only device /dev/sysgenid to userspace, which contains a > monotonically increasing u32 generation counter. Libraries and > applications are expected to open() the device, and then call read() > which blocks until the SysGenId changes. Following an update, read() > calls no longer block until the application acknowledges the new > SysGenId by write()ing it back to the device. Non-blocking read() calls > return EAGAIN when there is no new SysGenId available. Alternatively, > libraries can mmap() the device to get a single shared page which > contains the latest SysGenId at offset 0. Looking at some specifications, the gen ID might actually be located at an arbitrary address. How about instead of hard-coding the offset, we expose it e.g. in sysfs? > SysGenId also supports a notification mechanism exposed as two IOCTLs > on the device. SYSGENID_GET_OUTDATED_WATCHERS immediately returns the > number of file descriptors to the device that were open during the last > SysGenId change but have not yet acknowledged the new id. > SYSGENID_WAIT_WATCHERS blocks until there are no open file handles on > the device which haven’t acknowledged the new id. These two interfaces > are intended for serverless and container control planes, which want to > confirm that all application code has detected and reacted to the new > SysGenId before sending an invoke to the newly-restored sandbox. > > 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 > on VM snapshots. > > --- > > 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 > - renamed /dev/vmgenid -> /dev/sysgenid > - renamed uapi header file vmgenid.h -> sysgenid.h > - renamed ioctls VMGENID_* -> SYSGENID_* > - added ‘min_gen’ parameter to SYSGENID_FORCE_GEN_UPDATE ioctl > - fixed races in documentation examples > - various style nits > - rebased on top of linus latest > > 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 > - various nits > - rebase on top of linus latest > > Adrian Catangiu (2): > drivers/misc: sysgenid: add system generation id driver > drivers/virt: vmgenid: add vm generation id driver > > Documentation/misc-devices/sysgenid.rst | 240 +++++++++++++++++++++++++ > Documentation/virt/vmgenid.rst | 34 ++++ > drivers/misc/Kconfig | 16 ++ > drivers/misc/Makefile | 1 + > drivers/misc/sysgenid.c | 298 ++++++++++++++++++++++++++++++++ > drivers/virt/Kconfig | 14 ++ > drivers/virt/Makefile | 1 + > drivers/virt/vmgenid.c | 153 ++++++++++++++++ > include/uapi/linux/sysgenid.h | 18 ++ > 9 files changed, 775 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.
