powerpc/mm/numa: skip NUMA_NO_NODE onlining in parse_numa_properties()

Executing node_set_online() when nid = NUMA_NO_NODE results in an
undefined behavior. node_set_online() will call node_set_state(), into
__node_set(), into set_bit(), and since NUMA_NO_NODE is -1 we'll end up
doing a negative shift operation inside
arch/powerpc/include/asm/bitops.h. This potential UB was detected
running a kernel with CONFIG_UBSAN.

The behavior was introduced by commit 10f78fd0dabb ("powerpc/numa: Fix a
regression on memoryless node 0"), where the check for nid > 0 was
removed to fix a problem that was happening with nid = 0, but the result
is that now we're trying to online NUMA_NO_NODE nids as well.

Checking for nid >= 0 will allow node 0 to be onlined while avoiding
this UB with NUMA_NO_NODE.

Fixes: 10f78fd0dabb ("powerpc/numa: Fix a regression on memoryless node 0")
Reported-by: Ping Fang <pifang@redhat.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220224182312.1012527-1-danielhb413@gmail.com

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 9d5f710d2c2054dd33416169541668b6807927cf..b9b7fefbb64b9c7298ac718da6864b8b5b4c6a32 100644 (file)
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -956,7 +956,9 @@ static int __init parse_numa_properties(void)
                        of_node_put(cpu);
                }
 
-               node_set_online(nid);
+               /* node_set_online() is an UB if 'nid' is negative */
+               if (likely(nid >= 0))
+                       node_set_online(nid);
        }
 
        get_n_mem_cells(&n_mem_addr_cells, &n_mem_size_cells);