KVM: arm64: Ensure user_mem_abort() return value is initialised

If a change in the MMU notifier sequence number forces user_mem_abort()
to return early when attempting to handle a stage-2 fault, we return
uninitialised stack to kvm_handle_guest_abort(), which could potentially
result in the injection of an external abort into the guest or a spurious
return to userspace. Neither or these are what we want to do.

Initialise 'ret' to 0 in user_mem_abort() so that bailing due to a
change in the MMU notrifier sequence number is treated as though the
fault was handled.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Cc: Gavin Shan <gshan@redhat.com>
Cc: Alexandru Elisei <alexandru.elisei@arm.com>
Link: https://lore.kernel.org/r/20200930102442.16142-1-will@kernel.org

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index c5c26a9..a816cb8 100644 (file)
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -742,7 +742,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
                          struct kvm_memory_slot *memslot, unsigned long hva,
                          unsigned long fault_status)
 {
-       int ret;
+       int ret = 0;
        bool write_fault, writable, force_pte = false;
        bool exec_fault;
        bool device = false;