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[79.180.2.31]) by smtp.gmail.com with ESMTPSA id t8sm818884ejr.71.2021.02.24.01.05.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Feb 2021 01:05:10 -0800 (PST) Date: Wed, 24 Feb 2021 04:05:05 -0500 From: "Michael S. Tsirkin" To: Adrian Catangiu Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, kvm@vger.kernel.org, linux-s390@vger.kernel.org, gregkh@linuxfoundation.org, graf@amazon.com, rdunlap@infradead.org, arnd@arndb.de, ebiederm@xmission.com, rppt@kernel.org, 0x7f454c46@gmail.com, borntraeger@de.ibm.com, Jason@zx2c4.com, jannh@google.com, w@1wt.eu, colmmacc@amazon.com, luto@kernel.org, tytso@mit.edu, ebiggers@kernel.org, dwmw@amazon.co.uk, bonzini@gnu.org, sblbir@amazon.com, raduweis@amazon.com, corbet@lwn.net, mhocko@kernel.org, rafael@kernel.org, pavel@ucw.cz, mpe@ellerman.id.au, areber@redhat.com, ovzxemul@gmail.com, avagin@gmail.com, ptikhomirov@virtuozzo.com, gil@azul.com, asmehra@redhat.com, dgunigun@redhat.com, vijaysun@ca.ibm.com, oridgar@gmail.com, ghammer@redhat.com Subject: Re: [PATCH v7 0/2] System Generation ID driver and VMGENID backend Message-ID: <20210224040034-mutt-send-email-mst@kernel.org> References: <1614156452-17311-1-git-send-email-acatan@amazon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1614156452-17311-1-git-send-email-acatan@amazon.com> Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org 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.