Date: Mon, 08 Nov 2021 09:30:03 +0100 From: Florian Weimer <fweimer@...hat.com> To: Markus Wichmann <nullplan@....net> Cc: musl@...ts.openwall.com Subject: Re: add noexcept to all functions please * Markus Wichmann: > On Sun, Nov 07, 2021 at 07:20:21PM +0100, Florian Weimer wrote: >> I believe the musl cancellation implementation does not use DWARF >> unwinding. I do not know if it cancellation handlers have the same >> hardening gap as glibc's with setjmp-based unwinding. > I presume you mean the cancel cleanup handling. In that case, musl uses > a simple linked list, with nodes allocated on stack. No gaps of any > kind. The __f function pointer is stored in the node on the stack, along with the __x argument that is passed by _pthread_cleanup_pop. This looks like a convenient on-stack gadget for exploitation purposes. In musl, the invocation is in the library itself, so there isn't much choice there. In glibc, with -fno-exceptions, we try to avoid this by inlining the non-cancellation path at the pthread_cleanup_pop point. But even if the function pointer is constant, current GCC is no longer able to produce a direct call. But with -fexceptions, we do get a direct call. Thanks, Florian
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