On 2/18/2015 5:12 PM, grarpamp wrote:
The basic problem with this is that it makes two assumptions, both of which are dangerous.On Wed, Feb 18, 2015 at 5:16 PM, Tom Mitchell <mi...@niftyegg.com> wrote:The critical stage is the boot ROM (BIOS) and the boot device. Once Linux has booted a lot is possible but too much has already taken place. A BIOS that allows booting from a Flash memory card must be trusted.Virtual machines may help or hinder. The VM is sitting where the man in the middle wants to be and if it wants can protect or expose the OSs that it hosts. A VM can protect a hard drive from being infected by blocking vendor codes that might try to update or corrupt modern disks of boot flash memory.Afaik, all vm's today simply pass through all drive commands. It seems a move all the BSD's and Linux could make today, without waiting on untrustable hardware vendors to roll out signature verification in hardware, is to simply kernel block all commands unnecessary to actual production use of the disk. Permit only from a list of READ, WRITE, ERASE, INQ, TUR, RST, and so on. Thus every other command component, including firmware update, vendor specific, and binary fuzzing, gets dropped and logged. It could be done as a securelevel, or compiled in. It's definitely not bulletproof, but it does force adversaries to add that much more exploit code and effort to get root and go around the driver interface to access the hardware directly. Defense in depth. Similar tactics could be applied to other areas where firmware and vendor/fuzzable opcodes are involved... usb, bios and cpu.
1. The BIOS (which reads the boot sector) has not been compromised. If it has been you're hosed. Most if not all BIOS chips are field-programmable today which is both good and bad. It's good when you want to swap in a newer stepping CPU that wasn't formerly supported, it's bad when someone comes along and tampers with it. Hardware protection (e.g. a physical write-enable jumper on the board) would largely address this in terms of FIELD tampering (although not at the OEM level) but I know of nobody doing that right now. All my SuperMicro systems, for example, require nothing physical (e.g. a jumper to be installed) to enable a BIOS update.
2. Once the drive code has been tampered with you're in trouble because it is trivial for the drive to detect that the boot sector is being read and, if it is, to return something other than the real (unmolested) boot sector. That can then retrieve more corrupted things and now you're cooked.
I like barrier-protecting the I/O subsystem when running, but then again how many of these attacks are going to be loaded into your machine through a _*running*_ modern BSD-style system? I suspect the answer is "few" and a false sense of security is worse than none at all.
-- Karl Denninger k...@denninger.net <mailto:k...@denninger.net> /The Market Ticker/
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