linux-kernel - Re: [PATCH] arm64/smp: check !ipi_desc[i] in arch_show

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Date:   Wed, 15 Jun 2022 12:03:17 +0000
From:   "chenjun (AM)" <chenjun102@...wei.com>
To:     Will Deacon <will@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "xuqiang (M)" <xuqiang36@...wei.com>
Subject: Re: [PATCH] arm64/smp: check !ipi_desc[i] in arch_show_interrupts

在 2022/6/9 23:20, Will Deacon 写道:
> On Fri, May 27, 2022 at 08:22:36AM +0000, Chen Jun wrote:
>> There is a potential dereferencing null pointer issue in
>> arch_show_interrupts.
>>
>> Problem 1:
>> int arch_show_interrupts(struct seq_file *p, int prec)
>>          for (i = 0; i < NR_IPI; i++) {
>>                  seq_printf(p, "%10u ", irq_desc_kstat_cpu(ipi_desc[i],
>> 			cpu));
>>
>> Only ipi_desc[0..nr_ipi - 1] are initialized in set_smp_ipi_range.
>> and ipi_desc[nr_ipi..NR_IPI] are NULL.
>> irq_desc_kstat_cpu will dereference NULL pointer.
>> For now, the problem can not be triggered, because NR_IPI is always
>> equal to nr_ipi.
>>
>> Problem 2:
>> If request_percpu_irq failed in set_smp_ipi_range, ipi_desc[i]
>> would be NULL.
>> irq_desc_kstat_cpu will dereference NULL pointer.
>>
>> check !ipi_desc[i] (as arm does) to avoid the problem.
>>
>> Signed-off-by: Chen Jun <chenjun102@...wei.com>
>> ---
>>   arch/arm64/kernel/smp.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
>> index 62ed361a4376..3d54f464428b 100644
>> --- a/arch/arm64/kernel/smp.c
>> +++ b/arch/arm64/kernel/smp.c
>> @@ -781,6 +781,9 @@ int arch_show_interrupts(struct seq_file *p, int prec)
>>   	unsigned int cpu, i;
>>   
>>   	for (i = 0; i < NR_IPI; i++) {
>> +		if (!ipi_desc[i])
>> +			continue;
> 
> Why not just use nr_ipi instead of NR_IPI?

Yee, that is what I do at first. But I noticed that:

void __init set_smp_ipi_range(int ipi_base, int n)
     for (i = 0; i < nr_ipi; i++) {
         err = request_percpu_irq(ipi_base + i, ipi_handler,
                                  "IPI", &cpu_number);
         WARN_ON(err);
         ipi_desc[i] = irq_to_desc(ipi_base + i);

If request_percpu_irq return a error, I not sure if ipi_desc[i] makes sense.

> 
> Will
> 

-- 
Regards
Chen Jun