Patch "powerpc/mm/numa: skip NUMA_NO_NODE onlining in parse_numa_properties()" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     powerpc-mm-numa-skip-numa_no_node-onlining-in-parse_.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 69513628ee40ee9a4316732c984b949977d84034
Author: Daniel Henrique Barboza <danielhb413@xxxxxxxxx>
Date:   Thu Feb 24 15:23:12 2022 -0300

    powerpc/mm/numa: skip NUMA_NO_NODE onlining in parse_numa_properties()
    
    [ Upstream commit 749ed4a20657bcea66a6e082ca3dc0d228cbec80 ]
    
    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@xxxxxxxxxx>
    Signed-off-by: Daniel Henrique Barboza <danielhb413@xxxxxxxxx>
    Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20220224182312.1012527-1-danielhb413@xxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 59d3cfcd7887..5fb829256b59 100644
--- 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);