Re: [PATCH v3.18 backport] arm64: KVM: fix VTTBR_BADDR_MASK BUG_ON off-by-one

[Christoffer Dall <christoffer.dall@linaro.org>]

On Tue, Dec 12, 2017 at 01:50:31PM +0100, Christoffer Dall wrote:
> From: Kristina Martsenko <kristina.martsenko@arm.com>
> 
> Commit 26aa7b3b1c0fb3f1a6176a0c1847204ef4355693 upstream.

Please disregard this, I accidentally backported the arm64 patch
instead of the arm patch.

Another one (the correct one, hopefully) incoming, which backports
5553b142be11e794ebc0805950b2e8313f93d718 instead.

Thanks (and sorry about the noise),
-Christoffer

> 
> 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@vger.kernel.org> # 3.11.x
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
> Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
> ---
>  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 8afb863f5a9e..333ddd45dd1f 100644
> --- a/arch/arm64/include/asm/kvm_arm.h
> +++ b/arch/arm64/include/asm/kvm_arm.h
> @@ -160,8 +160,7 @@
>  #define VTTBR_X		(37 - VTCR_EL2_T0SZ_40B)
>  #endif
>  
> -#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	  (UL(0xFF) << VTTBR_VMID_SHIFT)
>  
> -- 
> 2.14.2
>