linux-kernel - Re: [PATCH 2/3] arm64: syscall.h: Add sign extension handling in syscall_get_return

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Date:   Tue, 20 Apr 2021 16:38:35 +0800
From:   He Zhe <zhe.he@...driver.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, paul@...l-moore.com,
        eparis@...hat.com, linux-audit@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] arm64: syscall.h: Add sign extension handling in
 syscall_get_return_value for compat



On 4/16/21 5:43 PM, Oleg Nesterov wrote:
> On 04/16, He Zhe wrote:
>> --- a/arch/arm64/include/asm/syscall.h
>> +++ b/arch/arm64/include/asm/syscall.h
>> @@ -44,7 +44,12 @@ static inline long syscall_get_error(struct task_struct *task,
>>  static inline long syscall_get_return_value(struct task_struct *task,
>>  					    struct pt_regs *regs)
>>  {
>> -	return regs->regs[0];
>> +	long val = regs->regs[0];
>> +
>> +	if (is_compat_thread(task_thread_info(task)))
>> +		val = sign_extend64(val, 31);
>> +
>> +	return val;
>>  }
> I can't really review these arm-specific patches, but with this change both
> syscall_get_error() and is_syscall_success() can use syscall_get_return_value()
> to avoid the code duplication.

Thanks. I'll improve this if v2 is needed.

Regards,
Zhe

>
> Oleg.
>