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Apple EFI Firmware Security Vulnerabilities

150 points by SpaceInvader 12y ago

fubarred 12y ago
Wanted: - "Tripwire" for firmware - host-based (not perfect) & bootable live cd/usb/image (still not perfect)... Perhaps some JTAG verifying device that could be hard-wired to all supported chips directly? (Very painful to setup, but potentially interesting.) - Host-based peripheral firewall (not perfect, but more usable) - e.g.: selectively disable, ask user permission and/or limit rights to connecting devices from the various buses: USB, FW, PCI, SD card, SATA/SAS, BT, TB, SPI, FC, ... On OSX, it's doable considering VMware Fusion "patches" IOKit (check out IORegistryExplorer) selectively based on user preferences (whether to redirect a USB device to a guest or to the host).
- makomk 12y ago
  In some cases, it's not possible to have a "Tripwire" equivalent for firmware. For example, Intel's Management Engine on modern chipsets runs code from a firmware region that's read-protected against access from user code.
- SCHiM 12y ago
  The second thing you mention already sort-of exists in the form of qubes os: https://qubes-os.org/ https://qubes-os.org/
userbinator 12y ago
Remember when BIOS flash ROMs were write-protected with a physical hardware switch/jumper? It was an extremely simple measure that basically made it impossible for the BIOS to be corrupted by software, malicious or otherwise. It was certainly "inconvenient" to perform BIOS updates, but back in those days BIOS updates weren't all that common either. I don't think it should ever be "convenient" to do something like that with basic system firmware - by its very nature, it is supposed to be stable and rarely changed. Somehow this is making me terribly nostalgic... for the days when BIOSes seemed far less buggy and in need of constant change. Now, I hear stories of laptops with factory-installed crap that silently updates the BIOS in the background(!), bricking the machine when something else unfortunate happens coincidentally with it (e.g. hard reset.) I remember the ritual of "boot from a floppy to a plain DOS prompt, run the updater, and wait for a few tense seconds as it updated the BIOS". The mention of "Thunderbolt Option ROM" makes it clear that Thunderbolt is basically an external version of PCI(e). In other words, even without being able to modify any firmware, plenty of other maliciousness is already possible - the same with any other device that has direct access to the system bus. In the same way that you probably wouldn't plug a random untrusted PCI(e) adapter into your system, you should exercise the same caution with Thunderbolt...
- mattstocum 12y ago
  Macs used to require a physical step in addition to the software setup to modify the boot ROM. I think it was something along the lines of load firmware update which initiates a reboot, after reboot press and hold the power button until there was a loud beep from the computer, then the firmware update could proceed. Not convenient, but more secure.
  - aroch 12y ago
    That's resetting the PRAM and was required on old macs for some of the fimrware changes to actually take place (since the firmware was cached).
    - mattstocum 12y ago
      No, resetting PRAM is triggered by holding down command-option-P-R. This was a special step that was required specifically for firmware updates.
      - thanksgiving 12y ago
        This reminds me of the hardware switch in the original Chromebook, the cr-48, which requires you to flip a switch underneath a piece of tape before you can install an alternative operating system. https://www.chromium.org/chromium-os/developer-information-for-chrome-os-devices/cr-48-chrome-notebook-developer-information https://www.chromium.org/chromium-os/developer-information-f...
        m45t3r 12y ago
        Actually, Chromebooks should be the most secure laptop platform nowadays, since every Chromebook has signed binaries and to enter in developer mode, you need some kind of switch so you can overwrite your bootloader. Of course, this is assuming Chromebooks' bootloader doesn't have any secured problems.
        12y ago
amluto 12y ago
> the larger issue of Apple's EFI firmware security and secure booting with no trusted hardware is more difficult to fix. IMO this shouldn't really be a problem. If the SPI payload disables writes before executing anything unsigned, then it's really quite hard to bypass. Presumably the bug is a result of EFI capsule on disk support. The design is sh*t for exactly this reason. The firmware could lock the flash, detect the capsule after initializing option ROMs, copy it to RAM, do a full reset, then find the capsule in RAM and verify a signature prior to re-locking the flash, though.
walterbell 12y ago
http://theinvisiblethings.blogspot.ca/2011/09/anti-evil-maid.html http://theinvisiblethings.blogspot.ca/2011/09/anti-evil-maid... "Anti Evil Maid is an implementation of a TPM-based static trusted boot with a primary goal to prevent Evil Maid attacks. The adjective trusted, in trusted boot, means that the goal of the mechanism is to somehow attest to a user that only desired (trusted) components have been loaded and executed during the system boot. It's a common mistake to confuse it with what is sometimes called secure boot, whose purpure is to prevent any unauthorized component from executing."
- sitkack 12y ago
  I was just coming here to say I would pay money for a pre-rootkit-rootkit. Someone has to get there first and it might as well be my own code.
walterbell 12y ago
http://puri.sm http://puri.sm "The first high-end laptop that respects your freedom and privacy. The Purism Librem 15 is the first laptop in the world that ships without mystery software in the kernel, operating system, or any software applications."
- rwmj 12y ago
  What CPU does it use? Does it need microcode? Interesting thread on exactly how free this laptop is: https://trisquel.info/en/forum/librem-15-freelibre-and-open-source-laptop-respects-your-essential-freedoms https://trisquel.info/en/forum/librem-15-freelibre-and-open-... (Edit: This post seems a bit harsh. My view is that any movement towards a more free laptop is welcome, especially since things like Android are going rapidly in the opposite direction)
  - zanny 12y ago
    You just won't get a blobless AMD or Intel computer. Intel for the chipset and CPU, AMD for the GPU firmware. And ARM is worse, since a majority of the ARM ecosystem just acts like bootloaders and their gpu drivers don't even exist.
- rasz_pl 12y ago
  >i7-4770HQ haha Intel cant even get rid of binary blobs from their official open source Atom platform (minnowboard). Intel UEFI bios is >100K lines of hand tuned spaghetti code that never saw version control system, thats straight from the mouth of Intel employee.
  - bjackman 12y ago
    Actually Intel run EDK2/Tianocore, the open-source "reference implementation" of UEFI. Its core functionality is pretty good quality, but the repo is huge and there's a lot of junk in there. Actual motherboards usually run (closed) forks of it.
  - RexRollman 12y ago
    I know that legacy BIOS has its issues, but from what I have seen and read, EFI/UEFI is a quagmire.
cnvogel 12y ago
Out of curiosity: Can anyone point me where to find how a recent x86-cpu actually boots? Where's the code that gets executed in the first few CPU cycles? The bulk of the firmware, that's clear, nowadays will be fetched from a serially connected flash, which this initial code will copy to the (then initialized) DRAM, also probably in several stages. But where do the first few instructions hide? Mask-rom in the CPU, or the chipset? I know how initial bootup works on my day-job-default-CPU (a m68k/coldfire that basically just starts executing from a parallel connected flash), on a few ARMs and some PPC, but I have no idea about a "typical" intel core/i5..7/... CPU.
- userbinator 12y ago
  The first "code" would probably be microcode in the CPU itself, but if you mean x86 instructions, recent CPUs boot in the same way as the orginal 8086: the first instruction after a reset is fetched from FFFF:FFF0, or 16 bytes less than the end of memory, in realmode. The BIOS ROM is mapped into this area. There are some good articles here: https://sites.google.com/site/pinczakko/ https://sites.google.com/site/pinczakko/
  - cnvogel 12y ago
    > the first instruction after a reset is fetched from FFFF:FFF0 I trust you that this logically will certainly be true, but: what memory will that access to ffff:fff0 be mapped to if the "bios" in my PC is stored in a SPI flash that certainly can't be connected directly to anything resembling a "address/data-bus" in a modern PC...
    - makomk 12y ago
      If I recall corretly, the access is mapped to the SPI flash chip which is memory-mapped into the CPU address space by the chipset. Access to this address range is of course relatively slow, but that's always been true of BIOS flash.
    - userbinator 12y ago
      There is circuitry that translates the requests from the CPU into read commands to the serial flash. Depending on the system, this can be in the LPC-connected SuperIO, the southbridge, or on laptops more likely part of the EC (embedded controller) which is also connected via LPC. This is also why executing from the BIOS is slow - SPI flash bandwidth is in the dozens of MB/s range, and if it's going over LPC the max bandwidth on that is <16MB/s. If you're really interested in this stuff the articles in the above link are a good read, as well as datasheets for the various chipsets involved. I'd recommend even looking at the original IBM PC/AT Technical Reference, with BIOS listings and full schematics.
abhv 12y ago
Can their be an external IO port that is both (a) fast and (b) access limited? -- BadUSB shows that the USB controller can fake keystrokes, modify the recipient USB controller, etc. -- This attack now shows an even more dangerous attack that can be mounted by a malicious thunderbolt adapter (the one that you unknowingly connected by habit at a conference, say). Trammell is giving a longer talk about this work at CCC next week. (http://events.ccc.de/congress/2014/Fahrplan/events/6128.html http://events.ccc.de/congress/2014/Fahrplan/events/6128.html) The attack is implemented (he has a demo macbook with "ThunderStruck" bootloader), and it has been disclosed to apple >400 days ago. One aspect of the attack can be patched with 2-byte change, but apparently apple hasn't bothered.
- jzwinck 12y ago
  > Can their be an external IO port that is both (a) fast and (b) access limited? Yes. eSATA is one example. 10 gigabit Ethernet is another. DisplayPort is, for certain applications.
markbnj 12y ago
Curious as to why the title is "EFI Firmware Security" and not "Apple EFI Firmware Security," which is the title of the piece linked?
- wmf 12y ago
  Do we have reason to believe that non-Apple implementations are any better? Most non-Apple computers don't have an external PCI bus, so there's that.
  - markbnj 12y ago
    No, not necessarily, and yet the article was specifically about an Apple exploit. Just seemed off to omit that from the post title.
- dang 12y ago
  No idea, but we changed it to agree with the article.
betafive 12y ago
Has anyone looked at using VTd to secure Thunderbolt devices from the system bus?
- amluto 12y ago
  That wouldn't help. This attack happens long before the OS loads, and EFI explicitly executes code from the option ROM, so DMA isn't even involved.
dominicgs 12y ago
I believe that the two year old Option ROM vulnerability to which this post refers was this one described by Loukas(snare) at Black Hat and Ruxcon 2012: https://www.youtube.com/watch?v=XcFvgAsfdqg https://www.youtube.com/watch?v=XcFvgAsfdqg Although I may be wrong, it's certainly a related vulnerability and an interesting presentation to watch. Skip to ~54mins if you just want to see the demo.
georgyo 12y ago
What I find most incredible about this is that apple has been told about this over and over again for the past 600 days, and did nothing would be the bigger issue. I have watched Trammel demonstrate this attach right in front of me about a year ago. Apple has repeatedly ignored the fact that they are vulnerable. It should also be noted that while this talk is Apple focused, it not a Apple thunderbolt specific attack. It affects all badly implemented thunderbolt ports. Apple's growing popularity and strong hardware standardization makes them especially susceptible to the wormificaiton of this attack. How many offices have a supply cabinet with thunderbolt to HDMI/Ethernet/other connectors that are shared around the office freely?
pix64 12y ago
Would it be possible to create a virtual thunderbolt port similar to virtual cd/dvd drives? and if so would that be vulnerable?

150 points by SpaceInvader 12y ago

Wanted: - "Tripwire" for firmware - host-based (not perfect) & bootable live cd/usb/image (still not perfect)... Perhaps some JTAG verifying device that could be hard-wired to all supported chips directly? (Very painful to setup, but potentially interesting.) - Host-based peripheral firewall (not perfect, but more usable) - e.g.: selectively disable, ask user permission and/or limit rights to connecting devices from the various buses: USB, FW, PCI, SD card, SATA/SAS, BT, TB, SPI, FC, ... On OSX, it's doable considering VMware Fusion "patches" IOKit (check out IORegistryExplorer) selectively based on user preferences (whether to redirect a USB device to a guest or to the host).

makomk 12y ago
In some cases, it's not possible to have a "Tripwire" equivalent for firmware. For example, Intel's Management Engine on modern chipsets runs code from a firmware region that's read-protected against access from user code.
SCHiM 12y ago
The second thing you mention already sort-of exists in the form of qubes os: https://qubes-os.org/ https://qubes-os.org/

userbinator 12y ago

Remember when BIOS flash ROMs were write-protected with a physical hardware switch/jumper? It was an extremely simple measure that basically made it impossible for the BIOS to be corrupted by software, malicious or otherwise. It was certainly "inconvenient" to perform BIOS updates, but back in those days BIOS updates weren't all that common either. I don't think it should ever be "convenient" to do something like that with basic system firmware - by its very nature, it is supposed to be stable and rarely changed. Somehow this is making me terribly nostalgic... for the days when BIOSes seemed far less buggy and in need of constant change. Now, I hear stories of laptops with factory-installed crap that silently updates the BIOS in the background(!), bricking the machine when something else unfortunate happens coincidentally with it (e.g. hard reset.) I remember the ritual of "boot from a floppy to a plain DOS prompt, run the updater, and wait for a few tense seconds as it updated the BIOS". The mention of "Thunderbolt Option ROM" makes it clear that Thunderbolt is basically an external version of PCI(e). In other words, even without being able to modify any firmware, plenty of other maliciousness is already possible - the same with any other device that has direct access to the system bus. In the same way that you probably wouldn't plug a random untrusted PCI(e) adapter into your system, you should exercise the same caution with Thunderbolt...

mattstocum 12y ago
Macs used to require a physical step in addition to the software setup to modify the boot ROM. I think it was something along the lines of load firmware update which initiates a reboot, after reboot press and hold the power button until there was a loud beep from the computer, then the firmware update could proceed. Not convenient, but more secure.
- aroch 12y ago
  That's resetting the PRAM and was required on old macs for some of the fimrware changes to actually take place (since the firmware was cached).
  - mattstocum 12y ago
    No, resetting PRAM is triggered by holding down command-option-P-R. This was a special step that was required specifically for firmware updates.
    - thanksgiving 12y ago
      This reminds me of the hardware switch in the original Chromebook, the cr-48, which requires you to flip a switch underneath a piece of tape before you can install an alternative operating system. https://www.chromium.org/chromium-os/developer-information-for-chrome-os-devices/cr-48-chrome-notebook-developer-information https://www.chromium.org/chromium-os/developer-information-f...
      - m45t3r 12y ago
        Actually, Chromebooks should be the most secure laptop platform nowadays, since every Chromebook has signed binaries and to enter in developer mode, you need some kind of switch so you can overwrite your bootloader. Of course, this is assuming Chromebooks' bootloader doesn't have any secured problems.
        12y ago

amluto 12y ago

> the larger issue of Apple's EFI firmware security and secure booting with no trusted hardware is more difficult to fix. IMO this shouldn't really be a problem. If the SPI payload disables writes before executing anything unsigned, then it's really quite hard to bypass. Presumably the bug is a result of EFI capsule on disk support. The design is sh*t for exactly this reason. The firmware could lock the flash, detect the capsule after initializing option ROMs, copy it to RAM, do a full reset, then find the capsule in RAM and verify a signature prior to re-locking the flash, though.

walterbell 12y ago

http://theinvisiblethings.blogspot.ca/2011/09/anti-evil-maid.html http://theinvisiblethings.blogspot.ca/2011/09/anti-evil-maid... "Anti Evil Maid is an implementation of a TPM-based static trusted boot with a primary goal to prevent Evil Maid attacks. The adjective trusted, in trusted boot, means that the goal of the mechanism is to somehow attest to a user that only desired (trusted) components have been loaded and executed during the system boot. It's a common mistake to confuse it with what is sometimes called secure boot, whose purpure is to prevent any unauthorized component from executing."

sitkack 12y ago
I was just coming here to say I would pay money for a pre-rootkit-rootkit. Someone has to get there first and it might as well be my own code.

walterbell 12y ago

http://puri.sm http://puri.sm "The first high-end laptop that respects your freedom and privacy. The Purism Librem 15 is the first laptop in the world that ships without mystery software in the kernel, operating system, or any software applications."

rwmj 12y ago
What CPU does it use? Does it need microcode? Interesting thread on exactly how free this laptop is: https://trisquel.info/en/forum/librem-15-freelibre-and-open-source-laptop-respects-your-essential-freedoms https://trisquel.info/en/forum/librem-15-freelibre-and-open-... (Edit: This post seems a bit harsh. My view is that any movement towards a more free laptop is welcome, especially since things like Android are going rapidly in the opposite direction)
- zanny 12y ago
  You just won't get a blobless AMD or Intel computer. Intel for the chipset and CPU, AMD for the GPU firmware. And ARM is worse, since a majority of the ARM ecosystem just acts like bootloaders and their gpu drivers don't even exist.
rasz_pl 12y ago
>i7-4770HQ haha Intel cant even get rid of binary blobs from their official open source Atom platform (minnowboard). Intel UEFI bios is >100K lines of hand tuned spaghetti code that never saw version control system, thats straight from the mouth of Intel employee.
- bjackman 12y ago
  Actually Intel run EDK2/Tianocore, the open-source "reference implementation" of UEFI. Its core functionality is pretty good quality, but the repo is huge and there's a lot of junk in there. Actual motherboards usually run (closed) forks of it.
- RexRollman 12y ago
  I know that legacy BIOS has its issues, but from what I have seen and read, EFI/UEFI is a quagmire.

cnvogel 12y ago

Out of curiosity: Can anyone point me where to find how a recent x86-cpu actually boots? Where's the code that gets executed in the first few CPU cycles? The bulk of the firmware, that's clear, nowadays will be fetched from a serially connected flash, which this initial code will copy to the (then initialized) DRAM, also probably in several stages. But where do the first few instructions hide? Mask-rom in the CPU, or the chipset? I know how initial bootup works on my day-job-default-CPU (a m68k/coldfire that basically just starts executing from a parallel connected flash), on a few ARMs and some PPC, but I have no idea about a "typical" intel core/i5..7/... CPU.

userbinator 12y ago
The first "code" would probably be microcode in the CPU itself, but if you mean x86 instructions, recent CPUs boot in the same way as the orginal 8086: the first instruction after a reset is fetched from FFFF:FFF0, or 16 bytes less than the end of memory, in realmode. The BIOS ROM is mapped into this area. There are some good articles here: https://sites.google.com/site/pinczakko/ https://sites.google.com/site/pinczakko/
- cnvogel 12y ago
  > the first instruction after a reset is fetched from FFFF:FFF0 I trust you that this logically will certainly be true, but: what memory will that access to ffff:fff0 be mapped to if the "bios" in my PC is stored in a SPI flash that certainly can't be connected directly to anything resembling a "address/data-bus" in a modern PC...
  - makomk 12y ago
    If I recall corretly, the access is mapped to the SPI flash chip which is memory-mapped into the CPU address space by the chipset. Access to this address range is of course relatively slow, but that's always been true of BIOS flash.
  - userbinator 12y ago
    There is circuitry that translates the requests from the CPU into read commands to the serial flash. Depending on the system, this can be in the LPC-connected SuperIO, the southbridge, or on laptops more likely part of the EC (embedded controller) which is also connected via LPC. This is also why executing from the BIOS is slow - SPI flash bandwidth is in the dozens of MB/s range, and if it's going over LPC the max bandwidth on that is <16MB/s. If you're really interested in this stuff the articles in the above link are a good read, as well as datasheets for the various chipsets involved. I'd recommend even looking at the original IBM PC/AT Technical Reference, with BIOS listings and full schematics.

abhv 12y ago

Can their be an external IO port that is both (a) fast and (b) access limited? -- BadUSB shows that the USB controller can fake keystrokes, modify the recipient USB controller, etc. -- This attack now shows an even more dangerous attack that can be mounted by a malicious thunderbolt adapter (the one that you unknowingly connected by habit at a conference, say). Trammell is giving a longer talk about this work at CCC next week. (http://events.ccc.de/congress/2014/Fahrplan/events/6128.html http://events.ccc.de/congress/2014/Fahrplan/events/6128.html) The attack is implemented (he has a demo macbook with "ThunderStruck" bootloader), and it has been disclosed to apple >400 days ago. One aspect of the attack can be patched with 2-byte change, but apparently apple hasn't bothered.

jzwinck 12y ago
> Can their be an external IO port that is both (a) fast and (b) access limited? Yes. eSATA is one example. 10 gigabit Ethernet is another. DisplayPort is, for certain applications.

markbnj 12y ago

Curious as to why the title is "EFI Firmware Security" and not "Apple EFI Firmware Security," which is the title of the piece linked?

wmf 12y ago
Do we have reason to believe that non-Apple implementations are any better? Most non-Apple computers don't have an external PCI bus, so there's that.
- markbnj 12y ago
  No, not necessarily, and yet the article was specifically about an Apple exploit. Just seemed off to omit that from the post title.
dang 12y ago
No idea, but we changed it to agree with the article.

betafive 12y ago

Has anyone looked at using VTd to secure Thunderbolt devices from the system bus?

amluto 12y ago
That wouldn't help. This attack happens long before the OS loads, and EFI explicitly executes code from the option ROM, so DMA isn't even involved.

dominicgs 12y ago

I believe that the two year old Option ROM vulnerability to which this post refers was this one described by Loukas(snare) at Black Hat and Ruxcon 2012: https://www.youtube.com/watch?v=XcFvgAsfdqg https://www.youtube.com/watch?v=XcFvgAsfdqg Although I may be wrong, it's certainly a related vulnerability and an interesting presentation to watch. Skip to ~54mins if you just want to see the demo.

georgyo 12y ago

What I find most incredible about this is that apple has been told about this over and over again for the past 600 days, and did nothing would be the bigger issue. I have watched Trammel demonstrate this attach right in front of me about a year ago. Apple has repeatedly ignored the fact that they are vulnerable. It should also be noted that while this talk is Apple focused, it not a Apple thunderbolt specific attack. It affects all badly implemented thunderbolt ports. Apple's growing popularity and strong hardware standardization makes them especially susceptible to the wormificaiton of this attack. How many offices have a supply cabinet with thunderbolt to HDMI/Ethernet/other connectors that are shared around the office freely?

pix64 12y ago

Would it be possible to create a virtual thunderbolt port similar to virtual cd/dvd drives? and if so would that be vulnerable?