From: Paolo Bonzini <pbonzini@redhat.com>
To: Marc Orr <marcorr@google.com>, dave.hansen@intel.com
Cc: kvm@vger.kernel.org, Jim Mattson <jmattson@google.com>,
David Rientjes <rientjes@google.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
linux-mm@kvack.org, akpm@linux-foundation.org,
rkrcmar@redhat.com, willy@infradead.org,
sean.j.christopherson@intel.com, dave.hansen@linux.intel.com,
Wanpeng Li <kernellwp@gmail.com>
Subject: Re: [kvm PATCH v6 2/2] kvm: x86: Dynamically allocate guest_fpu
Date: Mon, 5 Nov 2018 11:08:53 +0100 [thread overview]
Message-ID: <9c64321a-0050-c03e-b164-ab5782b70058@redhat.com> (raw)
In-Reply-To: <CAA03e5EU9j3tCLH=ZU8T4vz_N=D+2os_s8VcAYjC-o9cu-TJ0g@mail.gmail.com>
On 01/11/2018 18:35, Marc Orr wrote:
> Good question. Configuring the usercopy kmem cache to restrict access
> beyond fpu_user_xstate_size bytes (rather than fpu_kernel_xstate_size
> bytes) from the beginning of the state field seems intuitive to me,
> but I'm honestly not familiar with what user space expects KVM to
> return through the ioctls. Can someone familiar with this suggest what
> to do? Otherwise, I can update the patch to use the non-usercopy
> variant.
Similar to signal context, KVM always converts to non-compacted format
when copying out to userspace. KVM also needs to transmit supervisor
states, but that is done through KVM_GET/SET_MSRS rather than
KVM_GET/SET_XSAVE.
In addition, the userspace areas that are pointed to by the argument of
KVM_GET/SET_XSAVE and KVM_GET/SET_FPU are always accessed via
copy_to_user and memdup_user, in order to avoid possible TOCTTOU races.
Therefore, guest_fpu should not be usercopy at all.
Paolo
next prev parent reply other threads:[~2018-11-05 10:09 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-31 23:49 [kvm PATCH v6 0/2] shrink vcpu_vmx down to order 2 Marc Orr
2018-10-31 23:49 ` [kvm PATCH v6 1/2] kvm: x86: Use task structs fpu field for user Marc Orr
2018-10-31 23:49 ` [kvm PATCH v6 2/2] kvm: x86: Dynamically allocate guest_fpu Marc Orr
2018-11-01 17:09 ` Dave Hansen
2018-11-01 17:35 ` Marc Orr
2018-11-05 10:08 ` Paolo Bonzini [this message]
2018-11-05 5:04 ` [LKP] [kvm] ac347c1bc8: WARNING:at_mm/slab_common.c:#kmem_cache_create_usercopy kernel test robot
2021-05-21 20:58 ` [kvm PATCH v6 0/2] shrink vcpu_vmx down to order 2 Jim Mattson
2021-05-24 12:50 ` Paolo Bonzini
2021-05-24 22:44 ` Sean Christopherson
2021-05-24 23:01 ` Jim Mattson
2021-05-25 0:00 ` Sean Christopherson
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