• Paolo Bonzini's avatar
    KVM: fix bad user ABI for KVM_EXIT_SYSTEM_EVENT · d495f942
    Paolo Bonzini authored
    When KVM_EXIT_SYSTEM_EVENT was introduced, it included a flags
    member that at the time was unused.  Unfortunately this extensibility
    mechanism has several issues:
    
    - x86 is not writing the member, so it would not be possible to use it
      on x86 except for new events
    
    - the member is not aligned to 64 bits, so the definition of the
      uAPI struct is incorrect for 32- on 64-bit userspace.  This is a
      problem for RISC-V, which supports CONFIG_KVM_COMPAT, but fortunately
      usage of flags was only introduced in 5.18.
    
    Since padding has to be introduced, place a new field in there
    that tells if the flags field is valid.  To allow further extensibility,
    in fact, change flags to an array of 16 values, and store how many
    of the values are valid.  The availability of the new ndata field
    is tied to a system capability; all architectures are changed to
    fill in the field.
    
    To avoid breaking compilation of userspace that was using the flags
    field, provide a userspace-only union to overlap flags with data[0].
    The new field is placed at the same offset for both 32- and 64-bit
    userspace.
    
    Cc: Will Deacon <will@kernel.org>
    Cc: Marc Zyngier <maz@kernel.org>
    Cc: Peter Gonda <pgonda@google.com>
    Cc: Sean Christopherson <seanjc@google.com>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    Reported-by: default avatarkernel test robot <lkp@intel.com>
    Message-Id: <20220422103013.34832-1-pbonzini@redhat.com>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    d495f942
psci.c 15.5 KB