x86/int3: Avoid atomic instrumentation

Use arch_atomic_*() and __READ_ONCE() to ensure nothing untoward
creeps in and ruins things.

That is; this is the INT3 text poke handler, strictly limit the code
that runs in it, lest it inadvertenly hits yet another INT3.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/20200505135313.517429268@linutronix.de

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index dd81ed5beecab4eac9b75490829251e5615c4a7e..50a8d24a417ed64f1a5fe3ced99b3a595e48beab 100644 (file)
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1014,9 +1014,9 @@ static struct bp_patching_desc *bp_desc;
 static __always_inline
 struct bp_patching_desc *try_get_desc(struct bp_patching_desc **descp)
 {
-       struct bp_patching_desc *desc = READ_ONCE(*descp); /* rcu_dereference */
+       struct bp_patching_desc *desc = __READ_ONCE(*descp); /* rcu_dereference */
 
-       if (!desc || !atomic_inc_not_zero(&desc->refs))
+       if (!desc || !arch_atomic_inc_not_zero(&desc->refs))
                return NULL;
 
        return desc;
@@ -1025,7 +1025,7 @@ struct bp_patching_desc *try_get_desc(struct bp_patching_desc **descp)
 static __always_inline void put_desc(struct bp_patching_desc *desc)
 {
        smp_mb__before_atomic();
-       atomic_dec(&desc->refs);
+       arch_atomic_dec(&desc->refs);
 }
 
 static __always_inline void *text_poke_addr(struct text_poke_loc *tp)