linux-kernel - [PATCH v2 08/17] KVM: x86/mmu: Fix and unconditionally enable WARNs to detect PAE leaks

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Date:   Thu,  4 Mar 2021 17:10:52 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ben Gardon <bgardon@...gle.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: [PATCH v2 08/17] KVM: x86/mmu: Fix and unconditionally enable WARNs
 to detect PAE leaks

Exempt NULL PAE roots from the check to detect leaks, since
kvm_mmu_free_roots() doesn't set them back to INVALID_PAGE.  Stop hiding
the WARNs to detect PAE root leaks behind MMU_WARN_ON, the hidden WARNs
obviously didn't do their job given the hilarious number of bugs that
could lead to PAE roots being leaked, not to mention the above false
positive.

Opportunistically delete a warning on root_hpa being valid, there's
nothing special about 4/5-level shadow pages that warrants a WARN.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/mmu.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 9fc2b46f8541..b82c1b0d6d6e 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3250,7 +3250,8 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
 		mmu->root_hpa = root;
 	} else if (shadow_root_level == PT32E_ROOT_LEVEL) {
 		for (i = 0; i < 4; ++i) {
-			MMU_WARN_ON(VALID_PAGE(mmu->pae_root[i]));
+			WARN_ON_ONCE(mmu->pae_root[i] &&
+				     VALID_PAGE(mmu->pae_root[i]));
 
 			root = mmu_alloc_root(vcpu, i << (30 - PAGE_SHIFT),
 					      i << 30, PT32_ROOT_LEVEL, true);
@@ -3296,8 +3297,6 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
 	 * write-protect the guests page table root.
 	 */
 	if (mmu->root_level >= PT64_ROOT_4LEVEL) {
-		MMU_WARN_ON(VALID_PAGE(mmu->root_hpa));
-
 		root = mmu_alloc_root(vcpu, root_gfn, 0,
 				      mmu->shadow_root_level, false);
 		mmu->root_hpa = root;
@@ -3317,7 +3316,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
 	}
 
 	for (i = 0; i < 4; ++i) {
-		MMU_WARN_ON(VALID_PAGE(mmu->pae_root[i]));
+		WARN_ON_ONCE(mmu->pae_root[i] && VALID_PAGE(mmu->pae_root[i]));
 
 		if (mmu->root_level == PT32E_ROOT_LEVEL) {
 			if (!(pdptrs[i] & PT_PRESENT_MASK)) {
-- 
2.30.1.766.gb4fecdf3b7-goog