• Michael Ellerman's avatar
    powerpc/kernel: Enable seccomp filter · 2449acc5
    Michael Ellerman authored
    This commit enables seccomp filter on powerpc, now that we have all the
    necessary pieces in place.
    
    To support seccomp's desire to modify the syscall return value under
    some circumstances, we use a different ABI to the ptrace ABI. That is we
    use r3 as the syscall return value, and orig_gpr3 is the first syscall
    parameter.
    
    This means the seccomp code, or a ptracer via SECCOMP_RET_TRACE, will
    see -ENOSYS preloaded in r3. This is identical to the behaviour on x86,
    and allows seccomp or the ptracer to either leave the -ENOSYS or change
    it to something else, as well as rejecting or not the syscall by
    modifying r0.
    
    If seccomp does not reject the syscall, we restore the register state to
    match what ptrace and audit expect, ie. r3 is the first syscall
    parameter again. We do this restore using orig_gpr3, which may have been
    modified by seccomp, which allows seccomp to modify the first syscall
    paramater and allow the syscall to proceed.
    
    We need to #ifdef the the additional handling of r3 for seccomp, so move
    it all out of line.
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    Reviewed-by: default avatarKees Cook <keescook@chromium.org>
    2449acc5
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