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Fri, 25 Jun 2021 00:37:23 -0700 (PDT) Received: from localhost ([2401:fa00:8f:203:1492:9d4f:19fa:df61]) by smtp.gmail.com with UTF8SMTPSA id r4sm4766830pja.41.2021.06.25.00.37.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Jun 2021 00:37:23 -0700 (PDT) From: David Stevens X-Google-Original-From: David Stevens To: Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Paolo Bonzini , Nick Piggin Subject: [PATCH v2 1/5] KVM: do not allow mapping valid but non-refcounted pages Date: Fri, 25 Jun 2021 16:36:12 +0900 Message-Id: <20210625073616.2184426-2-stevensd@google.com> X-Mailer: git-send-email 2.32.0.93.g670b81a890-goog In-Reply-To: <20210625073616.2184426-1-stevensd@google.com> References: <20210625073616.2184426-1-stevensd@google.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kvm-ppc@vger.kernel.org, intel-gvt-dev@lists.freedesktop.org, Wanpeng Li , kvm@vger.kernel.org, Will Deacon , Suzuki K Poulose , Sean Christopherson , Joerg Roedel , linuxppc-dev@lists.ozlabs.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Zhenyu Wang , linux-mips@vger.kernel.org, James Morse , linux-arm-kernel@lists.infradead.org, intel-gfx@lists.freedesktop.org, Vitaly Kuznetsov , Alexandru Elisei , kvmarm@lists.cs.columbia.edu, Zhi Wang , Jim Mattson Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" From: Nicholas Piggin 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 the page if it was non-zero, which indicates it is participating in normal refcounting (and can be released with put_page). Signed-off-by: Nicholas Piggin --- virt/kvm/kvm_main.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 3dcc2abbfc60..f7445c3bcd90 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2175,6 +2175,13 @@ 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, bool *writable, @@ -2224,13 +2231,21 @@ 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. + * + * 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. */ - kvm_get_pfn(pfn); + if (!kvm_try_get_pfn(pfn)) + r = -EFAULT; out: pte_unmap_unlock(ptep, ptl); *p_pfn = pfn; - return 0; + + return r; } /* -- 2.32.0.93.g670b81a890-goog