linux-kernel - [PATCH 5.17 0620/1126] powerpc/mm/numa: skip NUMA_NO_NODE onlining in parse_numa

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Message-Id: <20220405070425.834178411@linuxfoundation.org>
Date:   Tue,  5 Apr 2022 09:22:47 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ping Fang <pifang@...hat.com>,
        Daniel Henrique Barboza <danielhb413@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.17 0620/1126] powerpc/mm/numa: skip NUMA_NO_NODE onlining in parse_numa_properties()

From: Daniel Henrique Barboza <danielhb413@...il.com>

[ 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@...hat.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@...il.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/20220224182312.1012527-1-danielhb413@gmail.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/powerpc/mm/numa.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 9d5f710d2c20..b9b7fefbb64b 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);
-- 
2.34.1