[PATCH] efi/libstub: arm/arm64: don't use TASK_SIZE when randomising the RT space

[Catalin Marinas]

On Mon, Apr 10, 2017 at 11:30:38AM +0100, Ard Biesheuvel wrote:
> As reported by James, Catalin and Mark, commit e69176d68d26
> ("ef/libstub/arm/arm64: Randomize the base of the UEFI rt services
> region") results in a crash in the firmware regardless of whether KASLR
> is in effect or not, and whether the firmware implements EFI_RNG_PROTOCOL
> or not.
> 
> Mark has identified the root cause to be the inappropriate use of
> TASK_SIZE in the stub, which arm64 defines as
> 
>   #define TASK_SIZE             (test_thread_flag(TIF_32BIT) ? \
>                                 TASK_SIZE_32 : TASK_SIZE_64)
> 
> and testing thread flags at this point results in the dereference of
> pointers in uninitialized structures.
> 
> So instead, introduce a preprocessor symbol EFI_RT_VIRTUAL_LIMIT and
> define it to TASK_SIZE_64 on arm64 and TASK_SIZE on ARM, both of which
> are compile time constants. Also, change the 'headroom' variable to
> static const to force an error if this changes in the future.
> 
> Cc: James Morse <james.morse at arm.com>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Matt Fleming <matt at codeblueprint.co.uk>
> Cc: Ingo Molnar <mingo at kernel.org>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>

It works for me as well:

Tested-by: Catalin Marinas <catalin.marinas at arm.com>

Thanks Ard and Mark.

-- 
Catalin