On Fri, Jul 21, 2023 at 06:23:48PM -0700, Sean Christopherson wrote:
> Explicitly check that tdp_iter_start() is handed a valid shadow page
> to harden KVM against bugs where
Sorry, where?
It's not about guest using an invisible GFN, it's about a KVM bug, right?
>
> Opportunistically stop the TDP MMU iteration instead of continuing on
> with garbage if the incoming root is bogus. Attempting to walk a garbage
> root is more likely to caused major problems than doing nothing.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> arch/x86/kvm/mmu/tdp_iter.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/tdp_iter.c b/arch/x86/kvm/mmu/tdp_iter.c
> index d2eb0d4f8710..bd30ebfb2f2c 100644
> --- a/arch/x86/kvm/mmu/tdp_iter.c
> +++ b/arch/x86/kvm/mmu/tdp_iter.c
> @@ -39,13 +39,14 @@ void tdp_iter_restart(struct tdp_iter *iter)
> void tdp_iter_start(struct tdp_iter *iter, struct kvm_mmu_page *root,
> int min_level, gfn_t next_last_level_gfn)
> {
> - int root_level = root->role.level;
> -
> - WARN_ON(root_level < 1);
> - WARN_ON(root_level > PT64_ROOT_MAX_LEVEL);
> + if (WARN_ON_ONCE(!root || (root->role.level < 1) ||
> + (root->role.level > PT64_ROOT_MAX_LEVEL))) {
> + iter->valid = false;
> + return;
> + }
>
I saw many usages of WARN_ON_ONCE() and WARN_ON() in KVM. And just wonder,
is there any criteria for KVM when to use which?
B.R.
Yu
