Re: [PATCH] arm64: fix fixmap copy for 16K pages and 48-bit VA

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 08/27/2019 09:27 PM, Mark Rutland wrote:
> With 16K pages and 48-bit VAs, the PGD level of table has two entries,
> and so the fixmap shares a PGD with the kernel image. Since commit:
> 
>   f9040773b7bbbd9e ("arm64: move kernel image to base of vmalloc area")
> 
> ... we copy the existing fixmap to the new fine-grained page tables at
> the PUD level in this case. When walking to the new PUD, we forgot to
> offset the PGD entry and always used the PGD entry at index 0, but this
> worked as the kernel image and fixmap were in the low half of the TTBR1
> address space.
> 
> As of commit:
> 
>   14c127c957c1c607 ("arm64: mm: Flip kernel VA space")
> 
> ... the kernel image and fixmap are in the high half of the TTBR1
> address space, and hence use the PGD at index 1, but we didn't update
> the fixmap copying code to account for this.
> 
> Thus, we'll erroneously try to copy the fixmap slots into a PUD under
> the PGD entry at index 0. At the point we do so this PGD entry has not
> been initialised, and thus we'll try to write a value to a small offset
> from physical address 0, causing a number of potential problems.
> 
> Fix this be correctly offsetting the PGD. This is split over a few steps
> for legibility.
> 
> Fixes: 14c127c957c1c607 ("arm64: mm: Flip kernel VA space")
> Reported-by: Anshuman Khandual <anshuman.khandual@arm.com>
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Steve Capper <Steve.Capper@arm.com>
> Cc: Will Deacon <will@kernel.org>

Tested-by: Anshuman Khandual <anshuman.khandual@arm.com>

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel