From: Christian Borntraeger <borntraeger@de.ibm.com>
To: Nicholas Piggin <npiggin@gmail.com>,
Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
Huacai Chen <chenhuacai@kernel.org>,
Marc Zyngier <maz@kernel.org>, Paul Mackerras <paulus@ozlabs.org>,
Paolo Bonzini <pbonzini@redhat.com>,
David Stevens <stevensd@chromium.org>,
Zhenyu Wang <zhenyuw@linux.intel.com>,
Zhi Wang <zhi.a.wang@intel.com>
Cc: Alexandru Elisei <alexandru.elisei@arm.com>,
dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org,
intel-gvt-dev@lists.freedesktop.org,
James Morse <james.morse@arm.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvmarm@lists.cs.columbia.edu, kvm-ppc@vger.kernel.org,
kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org,
Sean Christopherson <seanjc@google.com>,
David Stevens <stevensd@google.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>, Will Deacon <will@kernel.org>
Subject: Re: [PATCH 0/6] KVM: Remove uses of struct page from x86 and arm64 MMU
Date: Fri, 25 Jun 2021 09:44:31 +0200 [thread overview]
Message-ID: <19c4e392-fbab-ee2c-7039-c88d1ae5775d@de.ibm.com> (raw)
In-Reply-To: <1624539354.6zggpdrdbw.astroid@bobo.none>
On 24.06.21 14:57, Nicholas Piggin wrote:
> Excerpts from Paolo Bonzini's message of June 24, 2021 10:41 pm:
>> On 24/06/21 13:42, Nicholas Piggin wrote:
>>> Excerpts from Nicholas Piggin's message of June 24, 2021 8:34 pm:
>>>> Excerpts from David Stevens's message of June 24, 2021 1:57 pm:
>>>>> KVM supports mapping VM_IO and VM_PFNMAP memory into the guest by using
>>>>> follow_pte in gfn_to_pfn. However, the resolved pfns may not have
>>>>> assoicated struct pages, so they should not be passed to pfn_to_page.
>>>>> This series removes such calls from the x86 and arm64 secondary MMU. To
>>>>> do this, this series modifies gfn_to_pfn to return a struct page in
>>>>> addition to a pfn, if the hva was resolved by gup. This allows the
>>>>> caller to call put_page only when necessated by gup.
>>>>>
>>>>> This series provides a helper function that unwraps the new return type
>>>>> of gfn_to_pfn to provide behavior identical to the old behavior. As I
>>>>> have no hardware to test powerpc/mips changes, the function is used
>>>>> there for minimally invasive changes. Additionally, as gfn_to_page and
>>>>> gfn_to_pfn_cache are not integrated with mmu notifier, they cannot be
>>>>> easily changed over to only use pfns.
>>>>>
>>>>> This addresses CVE-2021-22543 on x86 and arm64.
>>>>
>>>> Does this fix the problem? (untested I don't have a POC setup at hand,
>>>> but at least in concept)
>>>
>>> This one actually compiles at least. Unfortunately I don't have much
>>> time in the near future to test, and I only just found out about this
>>> CVE a few hours ago.
>>
>> And it also works (the reproducer gets an infinite stream of userspace
>> exits and especially does not crash). We can still go for David's
>> solution later since MMU notifiers are able to deal with this pages, but
>> it's a very nice patch for stable kernels.
>
> Oh nice, thanks for testing. How's this?
>
> Thanks,
> Nick
>
> ---
>
> KVM: Fix page ref underflow for regions with valid but non-refcounted 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 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 <npiggin@gmail.com>
> ---
> 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 6a6bc7af0e28..46fb042837d2 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2055,6 +2055,13 @@ 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,
> @@ -2104,13 +2111,21 @@ 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;
>
Right. That should also take care of s390 (pin_guest_page in vsie.c
which calls gfn_to_page).
FWIW, the current API is really hard to follow as it does not tell
which functions take a reference and which dont.
Anyway, this patch (with cc stable?)
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
> out:
> pte_unmap_unlock(ptep, ptl);
> *p_pfn = pfn;
> - return 0;
> +
> + return r;
> }
>
> /*
>
prev parent reply other threads:[~2021-06-25 7:45 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-24 3:57 [PATCH 0/6] KVM: Remove uses of struct page from x86 and arm64 MMU David Stevens
2021-06-24 3:57 ` [PATCH 1/6] KVM: x86/mmu: release audited pfns David Stevens
2021-06-24 8:43 ` Nicholas Piggin
2021-06-24 9:43 ` Paolo Bonzini
2021-06-24 15:36 ` Sean Christopherson
2021-06-24 3:57 ` [PATCH 2/6] KVM: mmu: also return page from gfn_to_pfn David Stevens
2021-06-24 8:52 ` Nicholas Piggin
2021-06-24 9:42 ` Paolo Bonzini
2021-06-24 9:57 ` Nicholas Piggin
2021-06-24 10:13 ` Paolo Bonzini
2021-06-24 10:17 ` Nicholas Piggin
2021-06-24 10:21 ` Paolo Bonzini
2021-06-24 10:42 ` Nicholas Piggin
2021-06-24 9:40 ` Marc Zyngier
2021-06-24 3:57 ` [PATCH 3/6] KVM: x86/mmu: avoid struct page in MMU David Stevens
2021-06-24 7:31 ` Paolo Bonzini
2021-06-24 8:58 ` Nicholas Piggin
2021-06-24 10:06 ` Marc Zyngier
2021-06-24 10:17 ` Paolo Bonzini
2021-06-24 10:43 ` Nicholas Piggin
2021-06-24 3:57 ` [PATCH 4/6] KVM: arm64/mmu: " David Stevens
2021-06-24 10:43 ` Marc Zyngier
2021-06-24 3:57 ` [PATCH 5/6] KVM: mmu: remove over-aggressive warnings David Stevens
2021-06-24 3:57 ` [PATCH 6/6] drm/i915/gvt: use gfn_to_pfn's page instead of pfn David Stevens
2021-06-24 4:28 ` David Stevens
2021-06-24 6:57 ` [PATCH 0/6] KVM: Remove uses of struct page from x86 and arm64 MMU Paolo Bonzini
2021-06-24 10:34 ` Nicholas Piggin
2021-06-24 11:42 ` Nicholas Piggin
2021-06-24 12:00 ` Paolo Bonzini
2021-06-24 12:41 ` Paolo Bonzini
2021-06-24 12:57 ` Nicholas Piggin
2021-06-24 15:35 ` Paolo Bonzini
2021-06-25 0:20 ` Nicholas Piggin
2021-06-25 7:44 ` Christian Borntraeger [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=19c4e392-fbab-ee2c-7039-c88d1ae5775d@de.ibm.com \
--to=borntraeger@de.ibm.com \
--cc=aleksandar.qemu.devel@gmail.com \
--cc=alexandru.elisei@arm.com \
--cc=chenhuacai@kernel.org \
--cc=dri-devel@lists.freedesktop.org \
--cc=intel-gfx@lists.freedesktop.org \
--cc=intel-gvt-dev@lists.freedesktop.org \
--cc=james.morse@arm.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kvm-ppc@vger.kernel.org \
--cc=kvm@vger.kernel.org \
--cc=kvmarm@lists.cs.columbia.edu \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=maz@kernel.org \
--cc=npiggin@gmail.com \
--cc=paulus@ozlabs.org \
--cc=pbonzini@redhat.com \
--cc=seanjc@google.com \
--cc=stevensd@chromium.org \
--cc=stevensd@google.com \
--cc=suzuki.poulose@arm.com \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
--cc=will@kernel.org \
--cc=zhenyuw@linux.intel.com \
--cc=zhi.a.wang@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).