x86/alternatives: Sync core before enabling interrupts

commit 3ea1704a92967834bf0e64ca1205db4680d04048 upstream.

text_poke_early() does:

   local_irq_save(flags);
   memcpy(addr, opcode, len);
   local_irq_restore(flags);
   sync_core();

That's not really correct because the synchronization should happen before
interrupts are re-enabled to ensure that a pending interrupt observes the
complete update of the opcodes.

It's not entirely clear whether the interrupt entry provides enough
serialization already, but moving the sync_core() invocation into interrupt
disabled region does no harm and is obviously correct.

Fixes: 6fffacb30349 ("x86/alternatives, jumplabel: Use text_poke_early() before mm_init()")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/ZT6narvE%2BLxX%2B7Be@windriver.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 73be393..fd44739 100644 (file)
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1685,8 +1685,8 @@ void __init_or_module text_poke_early(void *addr, const void *opcode,
        } else {
                local_irq_save(flags);
                memcpy(addr, opcode, len);
-               local_irq_restore(flags);
                sync_core();
+               local_irq_restore(flags);
 
                /*
                 * Could also do a CLFLUSH here to speed up CPU recovery; but