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| author | James Hogan <james.hogan@imgtec.com> | 2016-06-15 18:29:57 (GMT) |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2016-06-15 21:58:36 (GMT) |
| commit | 42aa12e74e91f790d239bfb852260d07573ce83f (patch) | |
| tree | cf476b04bf159f8959fcce5340130bb823fbe1b2 /arch/mips/include | |
| parent | 05108709526716e1d40210fe3b9d7acd1cb694ea (diff) | |
| download | linux-42aa12e74e91f790d239bfb852260d07573ce83f.tar.xz | |
MIPS: KVM: Move commpage so 0x0 is unmapped
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>
Diffstat (limited to 'arch/mips/include')
| -rw-r--r-- | arch/mips/include/asm/kvm_host.h | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h index 5e9da2a..6c43c78 100644 --- a/arch/mips/include/asm/kvm_host.h +++ b/arch/mips/include/asm/kvm_host.h @@ -74,8 +74,14 @@ -/* Special address that contains the comm page, used for reducing # of traps */ -#define KVM_GUEST_COMMPAGE_ADDR 0x0 +/* + * Special address that contains the comm page, used for reducing # of traps + * This needs to be within 32Kb of 0x0 (so the zero register can be used), but + * preferably not at 0x0 so that most kernel NULL pointer dereferences can be + * caught. + */ +#define KVM_GUEST_COMMPAGE_ADDR ((PAGE_SIZE > 0x8000) ? 0 : \ + (0x8000 - PAGE_SIZE)) #define KVM_GUEST_KERNEL_MODE(vcpu) ((kvm_read_c0_guest_status(vcpu->arch.cop0) & (ST0_EXL | ST0_ERL)) || \ ((kvm_read_c0_guest_status(vcpu->arch.cop0) & KSU_USER) == 0)) |