Messages in this thread |  | | Date | Fri, 28 Jun 2019 12:45:11 -0700 (PDT) | From | Jaskaran Singh Khurana <> | Subject | Re: [RFC PATCH v5 0/1] Add dm verity root hash pkcs7 sig validation. |
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Hello Eric, On Thu, 27 Jun 2019, Eric Biggers wrote:
> 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 >
In a datacenter like environment, this will protect the system from below attacks:
1.Prevents attacker from deploying scripts that run arbitrary executables on the system. 2.Prevents physically present malicious admin to run arbitrary code on the machine.
Regards, Jaskaran
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