[kernel-hardening] Re: [PATCH 4/4] ef/libstub: arm/arm64: randomize the base of the UEFI rt services region

[James Morse <james.morse@arm.com>]

Hi Ard,

On 24/03/17 13:24, Ard Biesheuvel wrote:
> Update the allocation logic for the virtual mapping of the UEFI runtime
> services to start from a randomized base address if KASLR is in effect,
> and if the UEFI firmware exposes an implementation of EFI_RNG_PROTOCOL.
> 
> This makes it more difficult to predict the location of exploitable
> data structures in the runtime UEFI firmware, which increases robustness
> against attacks. Note that these regions are only mapped during the
> time a runtime service call is in progress, and only on a single CPU
> at a time, bit give the lack of a downside, let's enable it nonetheless.

With next-20170407 on Seattle Overdrive, I get an SError[0] on boot:

The three patches I have on top of 4.11.0-rc5-next-20170407 are:
* Revert "efi/libstub/arm*: Set default address and size cells values for an
empty dtb"
* Revert "ef/libstub/arm/arm64: Randomize the base of the UEFI rt services region"

At which point the machine start booting to a prompt again, (its noisier than
usual but looks like double-printing).

If I then cherry-pick:
* ef/libstub/arm/arm64: Randomize the base of the UEFI rt services region"

It again fails, producing the trace below. This is all with next-20170407's
defconfig, 4K/48. UEFI identifies itself as:
> UEFI v2.40 (American Megatrends, 0x0005000B)


Thanks,

James


[0]
Shell> efi\morse\Image console=ttyAMA0,115200 root=PARTUUID=b2edf709-3b28-4cb3-8
809-203f262e2bcc rw earlycon=pl011,0xe1010000 crashkernel=1G stacktrace ignore_l
oglevel=1 acpi=on efi=debug resume=/dev/sda3
EFI stub: Booting Linux Kernel...
EFI stub: Using DTB from configuration table
EFI stub: Exiting boot services and installing virtual address map...
[    0.000000] Booting Linux on physical CPU 0x0
[    0.000000] Linux version 4.11.0-rc5-next-20170407-00003-gbe65d54f8671 (morse
@melchizedek) (gcc version 4.9.3 20141031 (prerelease) (Linaro GCC 2014.11) ) #7
401 SMP PREEMPT Fri Apr 7 16:19:28 BST 2017
[    0.000000] Boot CPU: AArch64 Processor [411fd072]
[    0.000000] earlycon: pl11 at MMIO 0x00000000e1010000 (options '')
[    0.000000] bootconsole [pl11] enabled
[    0.000000] debug: ignoring loglevel setting.
[    0.000000] Bad mode in Error handler detected on CPU0, code 0xbf000000 -- SError
[    0.000000] Internal error: Oops - bad mode: 0 [#1] PREEMPT SMP
[    0.000000] Modules linked in:
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.11.0-rc5-next-20170407-
00003-gbe65d54f8671 #7401
[    0.000000] Hardware name: AMD Seattle (Rev.B0) Development Board (Overdrive)
 (DT)
[    0.000000] task: ffff000008e02b80 task.stack: ffff000008df0000
[    0.000000] PC is at setup_arch+0xf0/0x504
[    0.000000] LR is at setup_arch+0xec/0x504
[    0.000000] pc : [<ffff000008ce2844>] lr : [<ffff000008ce2840>] pstate: 000000c5

[    0.000000] Call trace:
[    0.000000] [<ffff000008ce2844>] setup_arch+0xf0/0x504
[    0.000000] [<ffff000008ce0838>] start_kernel+0x70/0x398
[    0.000000] [<ffff000008ce01e0>] __primary_switched+0x64/0x74
[    0.000000] Code: 9111c000 940034d9 97fff7cd d50344ff (90fffce3)
[    0.000000] ---[ end trace 0000000000000000 ]---
[    0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
[    0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task!