Hi Andrew, On 02/11/25 at 06:25pm, Baoquan He wrote: > On 02/07/25 at 04:08pm, Coiby Xu wrote: > > LUKS is the standard for Linux disk encryption, widely adopted by users, > > and in some cases, such as Confidential VMs, it is a requirement. With > > kdump enabled, when the first kernel crashes, the system can boot into > > the kdump/crash kernel to dump the memory image (i.e., /proc/vmcore) > > to a specified target. However, there are two challenges when dumping > > vmcore to a LUKS-encrypted device: > > > > - Kdump kernel may not be able to decrypt the LUKS partition. For some > > machines, a system administrator may not have a chance to enter the > > password to decrypt the device in kdump initramfs after the 1st kernel > > crashes; For cloud confidential VMs, depending on the policy the > > kdump kernel may not be able to unseal the keys with TPM and the > > console virtual keyboard is untrusted. > > > > - LUKS2 by default use the memory-hard Argon2 key derivation function > > which is quite memory-consuming compared to the limited memory reserved > > for kdump. Take Fedora example, by default, only 256M is reserved for > > systems having memory between 4G-64G. With LUKS enabled, ~1300M needs > > to be reserved for kdump. Note if the memory reserved for kdump can't > > be used by 1st kernel i.e. an user sees ~1300M memory missing in the > > 1st kernel. > > > > Besides users (at least for Fedora) usually expect kdump to work out of > > the box i.e. no manual password input or custom crashkernel value is > > needed. And it doesn't make sense to derivate the keys again in kdump > > kernel which seems to be redundant work. > > > > This patch set addresses the above issues by making the LUKS volume keys > > persistent for kdump kernel with the help of cryptsetup's new APIs > > (--link-vk-to-keyring/--volume-key-keyring). Here is the life cycle of > > the kdump copies of LUKS volume keys, > > > > 1. After the 1st kernel loads the initramfs during boot, systemd > > use an user-input passphrase to de-crypt the LUKS volume keys > > or TPM-sealed key and then save the volume keys to specified keyring > > (using the --link-vk-to-keyring API) and the key will expire within > > specified time. > > > > 2. A user space tool (kdump initramfs loader like kdump-utils) create > > key items inside /sys/kernel/config/crash_dm_crypt_keys to inform > > the 1st kernel which keys are needed. > > > > 3. When the kdump initramfs is loaded by the kexec_file_load > > syscall, the 1st kernel will iterate created key items, save the > > keys to kdump reserved memory. > > > > 4. When the 1st kernel crashes and the kdump initramfs is booted, the > > kdump initramfs asks the kdump kernel to create a user key using the > > key stored in kdump reserved memory by writing yes to > > /sys/kernel/crash_dm_crypt_keys/restore. Then the LUKS encrypted > > device is unlocked with libcryptsetup's --volume-key-keyring API. > > > > 5. The system gets rebooted to the 1st kernel after dumping vmcore to > > the LUKS encrypted device is finished > > > > After libcryptsetup saving the LUKS volume keys to specified keyring, > > whoever takes this should be responsible for the safety of these copies > > of keys. The keys will be saved in the memory area exclusively reserved > > for kdump where even the 1st kernel has no direct access. And further > > more, two additional protections are added, > > - save the copy randomly in kdump reserved memory as suggested by Jan > > - clear the _PAGE_PRESENT flag of the page that stores the copy as > > suggested by Pingfan > > > > This patch set only supports x86. There will be patches to support other > > architectures once this patch set gets merged. Could you pick this patchset into your tree since no conern from other reviewers? Thanks Baoquan > > This v8 looks good to me, thanks for the great effort, Coiby. > > Acked-by: Baoquan He <bhe@xxxxxxxxxx> >
