Commit 612e8e93 authored Jan 10, 2018 by Borislav Petkov Committed by Thomas Gleixner Jan 10, 2018

x86/alternatives: Fix optimize_nops() checking



The alternatives code checks only the first byte whether it is a NOP, but
with NOPs in front of the payload and having actual instructions after it
breaks the "optimized' test.

Make sure to scan all bytes before deciding to optimize the NOPs in there.

Reported-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Andrew Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linux-foundation.org>
Cc: Paul Turner <pjt@google.com>
Link: https://lkml.kernel.org/r/20180110112815.mgciyf5acwacphkq@pd.tnic

parent 9ecccfaa

arch/x86/kernel/alternative.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -344,9 +344,12 @@ recompute_jump(struct alt_instr a, u8 orig_insn, u8 repl_insn, u8 insnbuf)
		static void __init_or_module noinline optimize_nops(struct alt_instr a, u8 instr)
		{
		unsigned long flags;
		int i;

		if (instr[0] != 0x90)
		for (i = 0; i < a->padlen; i++) {
		if (instr[i] != 0x90)
		return;
		}

		local_irq_save(flags);
		add_nops(instr + (a->instrlen - a->padlen), a->padlen);