Date: Sun, 16 Sep 2018 23:23:17 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Replacing a_crash() ? Now that we have an abort() that reliably terminates with uncatchable SIGABRT, I've been thinking about replacing the a_crash() calls in musl (which are usually an instruction generating SIGILL or SIGSEGV) with calls to the uncatchable tail of abort(), which I would factor off as a __forced_abort() function. In case it's not clear, the reason for not just calling abort() is that too many programs catch it, and catching it is even encouraged. Catchability is a problem with the current approach too, since a_crash() is used in places where process state is known to be dangerously corrupt and likely under attacker control; eliminating it is one of the potential goals of switching to __forced_abort(). Are there any objections to making such a change? So far I've gotten mostly positive feedback -- SIGABRT is more telling of what's happened than SIGSEGV/SIGILL. It would also get rid of the ugly misplacement of a_crash() (no longer needed) in "atomic.h" and the inclusion of "atomic.h" in some files where it makes no sense without knowing it's where a_crash() is defined. For i386, some nontrivial work would be needed to make abort's tail perform syscalls with int $128 rather than the vdso, which is unsafe since the pointer to it may have been subverted. On other archs, inline syscalls are fully inline. I'd probably add a NEED_FAILSAFE_SYSCALL macro to define before including "syscall.h" and have arch/i386/syscall_arch.h adjust the asm string based on it; this is more maintainable than writing an asm version of the function. Rich
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