This small series picks up work from Amazon that seems to have stalled out last year around this time: listening for the vmgenid ACPI notification, and using it to "do something." Last year, folks proposed a complicated userspace mmap chardev, which was frought with difficulty and evidently abandoned. This year, instead, I have something much simpler in mind: simply using those ACPI notifications to tell the RNG to reinitialize safely, so we don't repeat random numbers in cloned, forked, or rolled-back VM instances. This series consists of two patches. The first one adds the right hooks into the actual RNG, and the second is a driver for the ACPI notification. I had posted an RFC v1 earlier today, thinking I really needed to request comments, lacking much experience with ACPI drivers. But having spent all day reworking this driver, and then testing and debugging it in a variety of circumstances, I feel fairly confident that it works well, so this is now the real thing. Please review! Here's a little screencast showing it in action: https://data.zx2c4.com/vmgenid-appears-to-work.gif As a side note, this series intentionally does _not_ focus on notification of these events to userspace or to other kernel consumers. Since these VM fork detection events first need to hit the RNG, we can later talk about what sorts of notifications or mmap'd counters the RNG should be making accessible to elsewhere. But that's a different sort of project and ties into a lot of more complicated concerns beyond this more basic patchset. So hopefully we can keep the discussion rather focused here to this ACPI business. Changes v1->v2: - [Ard] Correct value of MODULE_LICENSE(). - [Ard] Use ordinary memory accesses instead of memcpy_fromio. - [Ard] Make module a tristate and set MODULE_DEVICE_TABLE(). - [Ard] Free buffer after using. - Use { } instead of { "", 0 }. - Clean up interface into RNG. - Minimize ACPI driver a bit. In addition to the usual suspects, I'm CCing the original team from Amazon who proposed this last year and the QEMU developers who added it there, as well as the kernel Hyper-V maintainers, since this is technically a Microsoft-proposed thing, though QEMU now implements it. Cc: adrian@xxxxxxxxx Cc: dwmw@xxxxxxxxxxxx Cc: graf@xxxxxxxxxx Cc: colmmacc@xxxxxxxxxx Cc: raduweis@xxxxxxxxxx Cc: imammedo@xxxxxxxxxx Cc: ehabkost@xxxxxxxxxx Cc: ben@xxxxxxxxxxxxxxxxxx Cc: mst@xxxxxxxxxx Cc: kys@xxxxxxxxxxxxx Cc: haiyangz@xxxxxxxxxxxxx Cc: sthemmin@xxxxxxxxxxxxx Cc: wei.liu@xxxxxxxxxx Cc: decui@xxxxxxxxxxxxx Cc: linux@xxxxxxxxxxxxxxxxxxxx Cc: ardb@xxxxxxxxxx Cc: jannh@xxxxxxxxxx Cc: gregkh@xxxxxxxxxxxxxxxxxxx Cc: tytso@xxxxxxx Jason A. Donenfeld (2): random: add mechanism for VM forks to reinitialize crng virt: vmgenid: introduce driver for reinitializing RNG on VM fork drivers/char/random.c | 53 ++++++++++++++++++ drivers/virt/Kconfig | 9 ++++ drivers/virt/Makefile | 1 + drivers/virt/vmgenid.c | 120 +++++++++++++++++++++++++++++++++++++++++ include/linux/random.h | 1 + 5 files changed, 184 insertions(+) create mode 100644 drivers/virt/vmgenid.c -- 2.35.1
