[PATCH] arm64: KVM: fix VTTBR_BADDR_MASK BUG_ON off-by-one

[Christoffer Dall]

On Tue, Nov 14, 2017 at 02:37:43PM +0000, Kristina Martsenko wrote:
> VTTBR_BADDR_MASK is used to sanity check the size and alignment of the
> VTTBR address. It seems to currently be off by one, thereby only
> allowing up to 47-bit addresses (instead of 48-bit) and also
> insufficiently checking the alignment. This patch fixes it.
> 
> As an example, with 4k pages, before this patch we have:
> 
>   PHYS_MASK_SHIFT = 48
>   VTTBR_X = 37 - 24 = 13
>   VTTBR_BADDR_SHIFT = 13 - 1 = 12
>   VTTBR_BADDR_MASK = ((1 << 35) - 1) << 12 = 0x00007ffffffff000
> 
> Which is wrong, because the mask doesn't allow bit 47 of the VTTBR
> address to be set, and only requires the address to be 12-bit (4k)
> aligned, while it actually needs to be 13-bit (8k) aligned because we
> concatenate two 4k tables.
> 
> With this patch, the mask becomes 0x0000ffffffffe000, which is what we
> want.
> 
> Fixes: 0369f6a34b9f ("arm64: KVM: EL2 register definitions")
> Cc: <stable at vger.kernel.org> # 3.11.x
> Reviewed-by: Suzuki K Poulose <suzuki.poulose at arm.com>
> Signed-off-by: Kristina Martsenko <kristina.martsenko at arm.com>
> ---
>  arch/arm64/include/asm/kvm_arm.h | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
> index 61d694c2eae5..555d463c0eaa 100644
> --- a/arch/arm64/include/asm/kvm_arm.h
> +++ b/arch/arm64/include/asm/kvm_arm.h
> @@ -170,8 +170,7 @@
>  #define VTCR_EL2_FLAGS			(VTCR_EL2_COMMON_BITS | VTCR_EL2_TGRAN_FLAGS)
>  #define VTTBR_X				(VTTBR_X_TGRAN_MAGIC - VTCR_EL2_T0SZ_IPA)
>  
> -#define VTTBR_BADDR_SHIFT (VTTBR_X - 1)
> -#define VTTBR_BADDR_MASK  (((UL(1) << (PHYS_MASK_SHIFT - VTTBR_X)) - 1) << VTTBR_BADDR_SHIFT)
> +#define VTTBR_BADDR_MASK  (((UL(1) << (PHYS_MASK_SHIFT - VTTBR_X)) - 1) << VTTBR_X)
>  #define VTTBR_VMID_SHIFT  (UL(48))
>  #define VTTBR_VMID_MASK(size) (_AT(u64, (1 << size) - 1) << VTTBR_VMID_SHIFT)
>  
> -- 
> 2.1.4
> 

Reviewed-by: Christoffer Dall <christoffer.dall at linaro.org>