On Mon, Aug 06, 2018 at 06:39:58PM +0800, joeyli wrote: > On Mon, Aug 06, 2018 at 04:45:34PM +0800, Yu Chen wrote: > > Hi Pavel, > > On Sun, Aug 05, 2018 at 12:02:00PM +0200, Pavel Machek wrote: > > > Hi! > > > > > > > > User space doesn't need to involve. The EFI root key is generated by > > > > > EFI boot stub and be transfer to kernel. It's stored in EFI boot service > > > > > variable that it can only be accessed by trusted EFI binary when > > > > > secure boot is enabled. > > > > > > > > > Okay, this apply to the 'suspend' phase, right? > > > > I'm still a little confused about the 'resume' phase. > > > > Taking encryption as example(not signature), > > > > the purpose of doing hibernation encryption is to prevent other users > > > > from stealing ram content. Say, user A uses a passphrase to generate the > > > > > > No, I don't think that's purpose here. > > > > > > Purpose here is to prevent user from reading/modifying kernel memory > > > content on machine he owns. > > > > > Say, A puts his laptop into hibernation and walks away, > > and B walks by, and opens A's laptop and wakes up the system and he > > can do what he wants. Although EFI key/TPM trusted key is enabled, > > currently there's no certification during resume, which sounds > > unsafe to me. Afterall, the original requirement is to probe > > user for password during resume, which sounds more natural. > > OK, I saw your case. This is a physical accessing. > > I have a question: The suspend to memory also has the same behavior > and more people are using suspend. Should we think a common solution > to cover S3 and S4? > Since STD behaves more likely a boot up, STR does not have solid requirement for certification. > > > Strange as it may sound, that is what "secure" boot requires (and what > > > Disney wants). > > > > > Ok, I understand this requirement, and I'm also concerning how to > > distinguish different users from seeing data of each other. > > > > Joey, > > I'm thinking of a possible direction which could take advantage > > of the password. It leverages either EFI key or TPM > > trusted key to get it done. Does it make sense? > > > > 1. The user space generates a symetric key key_user using > > the password, and passes the key_user to the kernel as the master > > key. > > 2. The kernel uses the EFI key or TPM trusted key to encrypt > > the key_user thus gets a encrypt_key. > > 3. Uses the encrypt_key to do snapshot encryption > > 4. During resume, the same encrypt_key is generated following > > the same steps(I assume the same EFI key or TPM key could be fetched > > during resumed, right?) and do the snapshot decryption. > > > > Yes, we can use TPM key to protect the user key. But I suggest that we > should give user a function to disable the user key because not everyone > want to key-in a password for hibernate/resume and also snapshot image > encryption. > > Two policies: > - When user key-in user key, the snapshot image must be encryption. > - Without key-in user key, I still want the snapshot image can be encryption. > > No matter that the user key be key-in or not, the snapshot image must be > encrypted by a kernel key. So I suggest that we treat the user key as a salt > for snapshot image encryption and authentication. If the user key > be disabled, then kernel just generates a random number as a salt. > > Actually, the kernel must compares the user key before snapshot decryption. > If the user key doesn't match but user space still triggers furture resume > process. Then kernel direct drops the snapshot image. > Anyway I'm ok with using TPM for major 'security', please feel free to send a second version out, and for certification implementation we can have further discussion on that later. Best, Yu > > And this is what fscrypt is doing: > > Documentation/filesystems/fscrypt.rst > > > The use case is different. We have two key for two purposes. And the two > functions can be separated. > > Thanks > Joey Lee
