From: Petr Vandrovec Date: Sun, 12 Aug 2007 08:12:52 +0000 (+0200) Subject: Do not replace whole memcpy in apply alternatives X-Git-Tag: v2.6.23-rc3~7 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b8d3f2448b8f4ba24f301e23585547ba1acc1f04;p=linux-2.6 Do not replace whole memcpy in apply alternatives apply_alternatives uses memcpy() to apply alternatives. Which has the unfortunate effect that while applying memcpy alternative to memcpy itself it tries to overwrite itself with nops - which causes #UD fault as it overwrites half of an instruction in copy loop, and from this point on only possible outcome is triplefault and reboot. So let's overwrite only first two instructions of memcpy - as long as the main memcpy loop is not in first two bytes it will work fine. Signed-off-by: Petr Vandrovec Signed-off-by: Linus Torvalds --- diff --git a/arch/x86_64/lib/memcpy.S b/arch/x86_64/lib/memcpy.S index 0ea0ddc875..c22981fa2f 100644 --- a/arch/x86_64/lib/memcpy.S +++ b/arch/x86_64/lib/memcpy.S @@ -124,6 +124,8 @@ ENDPROC(__memcpy) .quad memcpy .quad 1b .byte X86_FEATURE_REP_GOOD - .byte .Lfinal - memcpy + /* Replace only beginning, memcpy is used to apply alternatives, so it + * is silly to overwrite itself with nops - reboot is only outcome... */ + .byte 2b - 1b .byte 2b - 1b .previous