[QUESTION] why redhat and others disable lcall7/lcall27?

From: Kirill Korotaev
Date: Fri Apr 29 2005 - 03:03:57 EST

All redhat kernels contain the patch given below which disables lcall7/lcall27. Why? I've heared from some people that these calls are insecure or something like that. But what is the real problem with it?
Why mainstream kernel still keeps these calls then?


diff -urNp linux-1130/arch/i386/kernel/traps.c linux-10000/arch/i386/kernel/traps.c
--- linux-1130/arch/i386/kernel/traps.c
+++ linux-10000/arch/i386/kernel/traps.c
@@ -1021,9 +1021,10 @@ void __init trap_init(void)
* default LDT is a single-entry callgate to lcall7 for iBCS
* and a callgate to lcall27 for Solaris/x86 binaries
+#if 0
* Should be a barrier for any external CPU state.

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