On Fri 2011-05-27 13:45:51, David Safford wrote: > On Thu, 2011-05-26 at 22:17 +0200, Pavel Machek wrote: > > > I suggest you explain the patchset in the emails, then? Everyone here > > seems to be confused... Attack it protects against, and what kind of > > hardware is needed for the protection to be effective? > > The white paper is over 15 pages, and it barely scratches the surface. > Every customer has different security threat models and requirements. > Discussing this in general on the mailing list is really hard. > > So let's try to simplify this just down to digital signatures in > the cellphone environment, as you state: Good. > > Because AFAICT, file signatures, as proposed, are only useful for > > locking down my cellphone against myself. (That's -- evil). > > The proposed digital signatures can enforce authenticity of a file's > data (IMA-Appraisal with Digital Signature), and of a file's metadata > (EVM with Digital Signature). For most users, enforcing authenticity > of files is a good thing - a user knows that they are running authentic > software signed by their phone manufacturer, and not malicious files > that they, or someone else installed. In this threat model, EVM is Ok, so lets talk about smartphone, similar to my HTC Dream (developer version, unlocked bootloader, flashable from kernel (*)). Yes, I could install the crazy EVM/IMA infastructure to prevent applications modifying selected files. But... I could just do chattr +i on selected files, I do not need fancy EVM/IMA for that. > Blocking signature verification would serve only to punish Linux > users who care about the authenticity of their files, while doing > _nothing_ to stop manufacturers from locking their bootloaders. chattr already protects authenticity of my files, as do standard unix permissions. So... where's the difference? Pavel (*) but it does not change anything. True; determined attacker could steal my cellphone, open it up, desolder the flash, and change attributes of the filesystem. But... the same determined attacker can also replace bootloader&kernel&filesystem -- that is in the same flash! -- with unlocked versions. So the argumentation is the same for locked down phone. -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
