[PATCH 5.4 13/17] KVM: Use kvm_pfn_t for local PFN variable in hva_to_pfn_remapped() - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Sean Christopherson <seanjc@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: [PATCH 5.4 13/17] KVM: Use kvm_pfn_t for local PFN variable in hva_to_pfn_remapped()
Date: Thu, 25 Feb 2021 10:53:58 +0100	[thread overview]
Message-ID: <20210225092515.648259854@linuxfoundation.org> (raw)
In-Reply-To: <20210225092515.001992375@linuxfoundation.org>

From: Sean Christopherson <seanjc@google.com>

commit a9545779ee9e9e103648f6f2552e73cfe808d0f4 upstream.

Use kvm_pfn_t, a.k.a. u64, for the local 'pfn' variable when retrieving
a so called "remapped" hva/pfn pair.  In theory, the hva could resolve to
a pfn in high memory on a 32-bit kernel.

This bug was inadvertantly exposed by commit bd2fae8da794 ("KVM: do not
assume PTE is writable after follow_pfn"), which added an error PFN value
to the mix, causing gcc to comlain about overflowing the unsigned long.

  arch/x86/kvm/../../../virt/kvm/kvm_main.c: In function ‘hva_to_pfn_remapped’:
  include/linux/kvm_host.h:89:30: error: conversion from ‘long long unsigned int’
                                  to ‘long unsigned int’ changes value from
                                  ‘9218868437227405314’ to ‘2’ [-Werror=overflow]
   89 | #define KVM_PFN_ERR_RO_FAULT (KVM_PFN_ERR_MASK + 2)
      |                              ^
virt/kvm/kvm_main.c:1935:9: note: in expansion of macro ‘KVM_PFN_ERR_RO_FAULT’

Cc: stable@vger.kernel.org
Fixes: add6a0cd1c5b ("KVM: MMU: try to fix up page faults before giving up")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210208201940.1258328-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 virt/kvm/kvm_main.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1598,7 +1598,7 @@ static int hva_to_pfn_remapped(struct vm
 			       bool write_fault, bool *writable,
 			       kvm_pfn_t *p_pfn)
 {
-	unsigned long pfn;
+	kvm_pfn_t pfn;
 	pte_t *ptep;
 	spinlock_t *ptl;
 	int r;


