linux-kernel - [PATCH] KVM: x86: do not pass poisoned hva to __kvm_set_memory

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Message-Id: <20200611180159.26085-1-pbonzini@redhat.com>
Date:   Thu, 11 Jun 2020 14:01:59 -0400
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH] KVM: x86: do not pass poisoned hva to __kvm_set_memory_region

__kvm_set_memory_region does not use the hva at all, so trying to
catch use-after-delete is pointless and, worse, it fails access_ok
now that we apply it to all memslots including private kernel ones.
This fixes an AVIC regression.

Fixes: 09d952c971a5 ("KVM: check userspace_addr for all memslots", 2020-06-01)
Reported-by: Maxim Levitsky <mlevitsk@...hat.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/x86.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 290784ba63e4..00c88c2f34e4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9951,13 +9951,8 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
 		if (!slot || !slot->npages)
 			return 0;
 
-		/*
-		 * Stuff a non-canonical value to catch use-after-delete.  This
-		 * ends up being 0 on 32-bit KVM, but there's no better
-		 * alternative.
-		 */
-		hva = (unsigned long)(0xdeadull << 48);
 		old_npages = slot->npages;
+		hva = 0;
 	}
 
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
-- 
2.26.2