From 710481f30b26856f462d3e5923bf69b32c12e097 Mon Sep 17 00:00:00 2001 From: Artem Savkov Date: Fri, 3 Sep 2021 16:00:17 +0200 Subject: [KPATCH CVE-2021-22543] KVM: do not allow mapping valid but non-reference-counted pages Kernels: 3.10.0-1160.el7 3.10.0-1160.2.1.el7 3.10.0-1160.2.2.el7 3.10.0-1160.6.1.el7 3.10.0-1160.11.1.el7 3.10.0-1160.15.2.el7 3.10.0-1160.21.1.el7 3.10.0-1160.24.1.el7 3.10.0-1160.25.1.el7 3.10.0-1160.31.1.el7 3.10.0-1160.36.2.el7 3.10.0-1160.41.1.el7 Changes since last build: [x86_64]: kvm_main.o: changed function: __gfn_to_pfn_memslot [ppc64le]: kvm_main.o: changed function: gfn_to_page kvm_main.o: changed function: gfn_to_pfn kvm_main.o: changed function: gfn_to_pfn_memslot kvm_main.o: changed function: gfn_to_pfn_prot kvm_main.o: changed function: hva_to_pfn kvm_main.o: changed function: kvm_vcpu_gfn_to_page kvm_main.o: changed function: kvm_vcpu_gfn_to_pfn --------------------------- Kernels: 3.10.0-1160.2.1.el7 3.10.0-1160.2.2.el7 3.10.0-1160.6.1.el7 3.10.0-1160.11.1.el7 3.10.0-1160.15.2.el7 3.10.0-1160.21.1.el7 3.10.0-1160.24.1.el7 3.10.0-1160.25.1.el7 3.10.0-1160.31.1.el7 3.10.0-1160.36.2.el7 3.10.0-1160.41.1.el7 3.10.0-1160.42.2.el7 Modifications: none Kpatch-MR: https://gitlab.com/kpatch-dev/rhel-7/-/merge_requests/7 Approved-by: Yannick Cote (@ycote1) Approved-by: Joe Lawrence (@joe.lawrence) Z-MR: https://gitlab.com/redhat/rhel/src/kernel/rhel-7/-/merge_requests/259 commit 64b6dd5036622d9fab20cea237ae19402a1a2ee3 Author: Jon Maloy Date: Tue Jul 13 15:28:38 2021 -0400 KVM: do not allow mapping valid but non-reference-counted pages Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1975511 Upstream: commit f8be156be163a052a067306417cd0ff679068c97 CVE-2021-22543 Brew: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=39156005 Conflicts: The upstream version hva_to_pfn_remapped() has been upgraded with lock support and a 'writeable' parameter. Those changes entail a code conflict, but not functional conflict, with this commit. commit f8be156be163a052a067306417cd0ff679068c97 Author: Nicholas Piggin Date: Thu Jun 24 08:29:04 2021 -0400 KVM: do not allow mapping valid but non-reference-counted pages It's possible to create a region which maps valid but non-refcounted pages (e.g., tail pages of non-compound higher order allocations). These host pages can then be returned by gfn_to_page, gfn_to_pfn, etc., family of APIs, which take a reference to the page, which takes it from 0 to 1. When the reference is dropped, this will free the page incorrectly. Fix this by only taking a reference on valid pages if it was non-zero, which indicates it is participating in normal refcounting (and can be released with put_page). This addresses CVE-2021-22543. Signed-off-by: Nicholas Piggin Tested-by: Paolo Bonzini Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini Signed-off-by: Jon Maloy Signed-off-by: Artem Savkov --- virt/kvm/kvm_main.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 4b01a017b262..2f40d5fe257d 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1479,6 +1479,13 @@ static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault) return true; } +static int kvm_try_get_pfn(kvm_pfn_t pfn) +{ + if (kvm_is_reserved_pfn(pfn)) + return 1; + return get_page_unless_zero(pfn_to_page(pfn)); +} + static int hva_to_pfn_remapped(struct vm_area_struct *vma, unsigned long addr, bool *async, bool write_fault, kvm_pfn_t *p_pfn) @@ -1514,11 +1521,19 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma, * Whoever called remap_pfn_range is also going to call e.g. * unmap_mapping_range before the underlying pages are freed, * causing a call to our MMU notifier. - */ - kvm_get_pfn(pfn); + * + * Certain IO or PFNMAP mappings can be backed with valid + * struct pages, but be allocated without refcounting e.g., + * tail pages of non-compound higher order allocations, which + * would then underflow the refcount when the caller does the + * required put_page. Don't allow those pages here. + */ + if (!kvm_try_get_pfn(pfn)) + r = -EFAULT; *p_pfn = pfn; - return 0; + + return r; } /* -- 2.26.3