On Wed, Jun 19, 2019 at 12:10:47PM -0700, Jaskaran Khurana wrote: > This patch set adds in-kernel pkcs7 signature checking for the roothash of > the dm-verity hash tree. > The verification is to support cases where the roothash is not secured by > Trusted Boot, UEFI Secureboot or similar technologies. > One of the use cases for this is for dm-verity volumes mounted after boot, > the root hash provided during the creation of the dm-verity volume has to > be secure and thus in-kernel validation implemented here will be used > before we trust the root hash and allow the block device to be created. > > Why we are doing validation in the Kernel? > > The reason is to still be secure in cases where the attacker is able to > compromise the user mode application in which case the user mode validation > could not have been trusted. > The root hash signature validation in the kernel along with existing > dm-verity implementation gives a higher level of confidence in the > executable code or the protected data. Before allowing the creation of > the device mapper block device the kernel code will check that the detached > pkcs7 signature passed to it validates the roothash and the signature is > trusted by builtin keys set at kernel creation. The kernel should be > secured using Verified boot, UEFI Secure Boot or similar technologies so we > can trust it. > > What about attacker mounting non dm-verity volumes to run executable > code? > > This verification can be used to have a security architecture where a LSM > can enforce this verification for all the volumes and by doing this it can > ensure that all executable code runs from signed and trusted dm-verity > volumes. > > Further patches will be posted that build on this and enforce this > verification based on policy for all the volumes on the system. > I don't understand your justification for this feature. If userspace has already been pwned severely enough for the attacker to be executing arbitrary code with CAP_SYS_ADMIN (which is what the device mapper ioctls need), what good are restrictions on loading more binaries from disk? Please explain your security model. - Eric -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
