linux-kernel - [PATCH 1/2] KVM: x86/mmu: Bug the VM if KVM tries to split a !hugepage SPTE

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240712151335.1242633-2-seanjc@google.com>
Date: Fri, 12 Jul 2024 08:13:34 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	David Matlack <dmatlack@...gle.com>
Subject: [PATCH 1/2] KVM: x86/mmu: Bug the VM if KVM tries to split a
 !hugepage SPTE

Bug the VM instead of simply warning if KVM tries to split a SPTE that is
non-present or not-huge.  KVM is guaranteed to end up in a broken state as
the callers fully expect a valid SPTE, e.g. the shadow MMU will add an
rmap entry, and all MMUs will account the expected small page.  Returning
'0' is also technically wrong now that SHADOW_NONPRESENT_VALUE exists,
i.e. would cause KVM to create a potential #VE SPTE.

While it would be possible to have the callers gracefully handle failure,
doing so would provide no practical value as the scenario really should be
impossible, while the error handling would add a non-trivial amount of
noise.

Fixes: a3fe5dbda0a4 ("KVM: x86/mmu: Split huge pages mapped by the TDP MMU when dirty logging is enabled")
Cc: David Matlack <dmatlack@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/spte.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index c8fe13217ff7..bc55e3b26045 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -296,11 +296,7 @@ u64 make_huge_page_split_spte(struct kvm *kvm, u64 huge_spte, union kvm_mmu_page
 {
 	u64 child_spte;

-	if (WARN_ON_ONCE(!is_shadow_present_pte(huge_spte)))
-		return 0;
-
-	if (WARN_ON_ONCE(!is_large_pte(huge_spte)))
-		return 0;
+	KVM_BUG_ON(!is_shadow_present_pte(huge_spte) || !is_large_pte(huge_spte), kvm);

 	child_spte = huge_spte;

-- 
2.45.2.993.g49e7a77208-goog