linux-kernel - [PATCH 5.10 v3] locking/csd_lock: fix csdlock

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Date:   Sat, 7 May 2022 16:45:10 +0800
From:   Chen Zhongjin <chenzhongjin@...wei.com>
To:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-arch@...r.kernel.org>, <stable@...r.kernel.org>
CC:     <peterz@...radead.org>, <tglx@...utronix.de>, <namit@...are.com>,
        <gor@...ux.ibm.com>, <rdunlap@...radead.org>,
        <gregkh@...uxfoundation.org>, <sashal@...nel.org>,
        <chenzhongjin@...wei.com>
Subject: [PATCH 5.10 v3] locking/csd_lock: fix csdlock_debug cause arm64 boot panic

csdlock_debug is a early_param to enable csd_lock_wait
feature.

It uses static_branch_enable in early_param which triggers
a panic on arm64 with config:
CONFIG_SPARSEMEM=y
CONFIG_SPARSEMEM_VMEMMAP=n

The log shows:
Unable to handle kernel NULL pointer dereference at
virtual address ", '0' <repeats 16 times>, "
...
Call trace:
__aarch64_insn_write+0x9c/0x18c
...
static_key_enable+0x1c/0x30
csdlock_debug+0x4c/0x78
do_early_param+0x9c/0xcc
parse_args+0x26c/0x3a8
parse_early_options+0x34/0x40
parse_early_param+0x80/0xa4
setup_arch+0x150/0x6c8
start_kernel+0x8c/0x720
...
Kernel panic - not syncing: Oops: Fatal exception

Call trace inside __aarch64_insn_write:
__nr_to_section
__pfn_to_page
phys_to_page
patch_map
__aarch64_insn_write

Here, with CONFIG_SPARSEMEM_VMEMMAP=n, __nr_to_section returns
NULL and makes the NULL dereference because mem_section is
initialized in sparse_init after parse_early_param stage.

So, static_branch_enable shouldn't be used inside early_param.
To avoid this, I changed it to __setup and fixed this.

Reported-by: Chen jingwen <chenjingwen6@...wei.com>
Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
---
Change v2 -> v3:
Add module name in title

Change v1 -> v2:
Fix return 1 for __setup
---

 kernel/smp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index 65a630f62363..381eb15cd28f 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -174,9 +174,9 @@ static int __init csdlock_debug(char *str)
 	if (val)
 		static_branch_enable(&csdlock_debug_enabled);

-	return 0;
+	return 1;
 }
-early_param("csdlock_debug", csdlock_debug);
+__setup("csdlock_debug=", csdlock_debug);

 static DEFINE_PER_CPU(call_single_data_t *, cur_csd);
 static DEFINE_PER_CPU(smp_call_func_t, cur_csd_func);
-- 
2.17.1