x86/alternatives: Fix optimize_nops() checking

commit 612e8e9350fd19cae6900cf36ea0c6892d1a0dca upstream.

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
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit e997d991ab2b1dc9f9cdad999a891626c2aecf21)
Orabug: 27477743
CVE: CVE-2017-5715
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 7aaad2f3648b4774db7795e7be65df88849c9be9..55f86af5392f6df68df8cdff66a52c62a371d5e0 100644 (file)
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -326,9 +326,12 @@ done:
 static void __init_or_module optimize_nops(struct alt_instr *a, u8 *instr)
 {
        unsigned long flags;
+       int i;
 
-       if (instr[0] != 0x90)
-               return;
+       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);