[PATCH v2 2/3] KVM: PPC: Book3S HV: Add sanity check to copy_tofrom_guest

[Nicholas Piggin]

Excerpts from Fabiano Rosas's message of August 6, 2021 7:26 am:
> Both paths into __kvmhv_copy_tofrom_guest_radix ensure that we arrive
> with an effective address that is smaller than our total addressable
> space and addresses quadrant 0.
> 
> - The H_COPY_TOFROM_GUEST hypercall path rejects the call with
> H_PARAMETER if the effective address has any of the twelve most
> significant bits set.
> 
> - The kvmhv_copy_tofrom_guest_radix path clears the top twelve bits
> before calling the internal function.
> 
> Although the callers make sure that the effective address is sane, any
> future use of the function is exposed to a programming error, so add a
> sanity check.

We possibly should put these into #defines in radix pgtable headers 
somewhere but KVM already open codes them so this is good for now.

Reviewed-by: Nicholas Piggin <npiggin at gmail.com>

> 
> Suggested-by: Nicholas Piggin <npiggin at gmail.com>
> Signed-off-by: Fabiano Rosas <farosas at linux.ibm.com>
> ---
>  arch/powerpc/kvm/book3s_64_mmu_radix.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
> index 44eb7b1ef289..1b1c9e9e539b 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
> @@ -44,6 +44,9 @@ unsigned long __kvmhv_copy_tofrom_guest_radix(int lpid, int pid,
>  					  (to != NULL) ? __pa(to): 0,
>  					  (from != NULL) ? __pa(from): 0, n);
>  
> +	if (eaddr & (0xFFFUL << 52))
> +		return ret;
> +
>  	quadrant = 1;
>  	if (!pid)
>  		quadrant = 2;
> -- 
> 2.29.2
> 
>