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MIPS: KVM: Move commpage so 0x0 is unmapped

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The comm page which is mapped into the guest kernel address space at
0x0 has the unfortunate side effect of allowing guest kernel NULL
pointer dereferences to succeed. The only constraint on this address is
that it must be within 32KiB of 0x0, so that single lw/sw instructions
(which have 16-bit signed offset fields) can be used to access it, using
the zero register as a base.

So lets move the comm page as high as possible within that constraint so
that 0x0 can be left unmapped, at least for page sizes < 32KiB.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
James Hogan
2016-06-15 19:29:57 +01:00
committed by Paolo Bonzini
parent 0510870952
commit 42aa12e74e
4 changed files with 20 additions and 14 deletions
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2
arch/mips/kvm/commpage.c
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@@ -4,7 +4,7 @@
* for more details.
*
* commpage, currently used for Virtual COP0 registers.
* Mapped into the guest kernel @ 0x0.
* Mapped into the guest kernel @ KVM_GUEST_COMMPAGE_ADDR.
*
* Copyright (C) 2012 MIPS Technologies, Inc. All rights reserved.
* Authors: Sanjay Lal <sanjayl@kymasys.com>