c18n: Allow system calls only for code with CHERI_PERM_SYSCALL and secure mmap #2320
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This PR removes the
CHERI_PERM_SYSCALLpermission from all libraries exceptlibsys.Previously, the kernel returns
ECAPMODEfor callers withoutCHERI_PERM_SYSCALLand optionally enters KDB when that happens. This PR removes the legacy KDB behavior and instead raises a signal (by callingnosys). This is superior to the old behavior because it makes debugging easier.(Sadly it seems that the best place to cause
nosysto be called is in MD code. I wonder if there's a better place to do it without disrupting tracing.)This PR also interposes
mmapand removesCHERI_PERM_EXECUTIVEandCHERI_PERM_SYSCALLfrom any value returned.