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| author | Paolo Bonzini <pbonzini@redhat.com> | 2021-02-01 05:12:11 -0500 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-07-28 11:13:51 +0200 |
| commit | 918e0039ec570aec22338a405bfd6dab1264de30 (patch) | |
| tree | 00a300566cb17520dcce115b074c092c7be6fd47 /virt/kvm | |
| parent | 020a44cc54d65e673a13195e96fc0addbfd3a601 (diff) | |
| download | linux-stable-918e0039ec570aec22338a405bfd6dab1264de30.tar.gz linux-stable-918e0039ec570aec22338a405bfd6dab1264de30.tar.bz2 linux-stable-918e0039ec570aec22338a405bfd6dab1264de30.zip | |
KVM: do not assume PTE is writable after follow_pfn
commit bd2fae8da794b55bf2ac02632da3a151b10e664c upstream.
In order to convert an HVA to a PFN, KVM usually tries to use
the get_user_pages family of functinso. This however is not
possible for VM_IO vmas; in that case, KVM instead uses follow_pfn.
In doing this however KVM loses the information on whether the
PFN is writable. That is usually not a problem because the main
use of VM_IO vmas with KVM is for BARs in PCI device assignment,
however it is a bug. To fix it, use follow_pte and check pte_write
while under the protection of the PTE lock. The information can
be used to fail hva_to_pfn_remapped or passed back to the
caller via *writable.
Usage of follow_pfn was introduced in commit add6a0cd1c5b ("KVM: MMU: try to fix
up page faults before giving up", 2016-07-05); however, even older version
have the same issue, all the way back to commit 2e2e3738af33 ("KVM:
Handle vma regions with no backing page", 2008-07-20), as they also did
not check whether the PFN was writable.
Fixes: 2e2e3738af33 ("KVM: Handle vma regions with no backing page")
Reported-by: David Stevens <stevensd@google.com>
Cc: 3pvd@google.com
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[OP: backport to 4.19, adjust follow_pte() -> follow_pte_pmd()]
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'virt/kvm')
| -rw-r--r-- | virt/kvm/kvm_main.c | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 1ecb27b3421a..6aeac96bf147 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1495,9 +1495,11 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma, kvm_pfn_t *p_pfn) { unsigned long pfn; + pte_t *ptep; + spinlock_t *ptl; int r; - r = follow_pfn(vma, addr, &pfn); + r = follow_pte_pmd(vma->vm_mm, addr, NULL, NULL, &ptep, NULL, &ptl); if (r) { /* * get_user_pages fails for VM_IO and VM_PFNMAP vmas and does @@ -1512,14 +1514,19 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma, if (r) return r; - r = follow_pfn(vma, addr, &pfn); + r = follow_pte_pmd(vma->vm_mm, addr, NULL, NULL, &ptep, NULL, &ptl); if (r) return r; + } + if (write_fault && !pte_write(*ptep)) { + pfn = KVM_PFN_ERR_RO_FAULT; + goto out; } if (writable) - *writable = true; + *writable = pte_write(*ptep); + pfn = pte_pfn(*ptep); /* * Get a reference here because callers of *hva_to_pfn* and @@ -1534,6 +1541,8 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma, */ kvm_get_pfn(pfn); +out: + pte_unmap_unlock(ptep, ptl); *p_pfn = pfn; return 0; } |