amd64: strictly enforce the caller's mode for FRED 64bit syscall handler in CHEADmain

For FRED SYSCALL calls, check that the LM bit is set.

Note that this handler is redundant for 64bit mode since syscalls
are handled by the asm fast path. Intel CPUs raise #UD for SYSCALL
in the compatibility mode, and for AMD we set up the MSR_CSTAR to
fast_syscall32 for IDT case, which is nop. So practically it should only
matter if AMD CPUs with FRED enabled allow SYSCALL from compatibility
mode.

Reported and reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

0 files changed, 0 insertions, 0 deletions