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Subject[PATCH] KVM: Use kvm_pfn_t for local PFN variable in hva_to_pfn_remapped()
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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>
---

I don't actually know that it's possible for a remapped pfn to be a 64-bit
value on a stock kernel. But, backporting a one-liner is far easier and
safer than trying to audit all possible flows. :-)

virt/kvm/kvm_main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index ee4ac2618ec5..001b9de4e727 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1906,7 +1906,7 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma,
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;
--
2.30.0.478.g8a0d178c01-goog
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