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

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Date:   Fri, 16 Apr 2021 11:43:25 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     He Zhe <zhe.he@...driver.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 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.

Oleg.