linux-kernel - Re: [patch 1/5] lib/vdso/32: Remove inconsistent NULL pointer checks

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Message-ID: <dafaa6b5-8e45-307c-c65a-dfef467a5754@arm.com>
Date:   Sun, 28 Jul 2019 16:30:07 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Paul Bolle <pebolle@...cali.nl>, Will Deacon <will@...nel.org>
Subject: Re: [patch 1/5] lib/vdso/32: Remove inconsistent NULL pointer checks

On 7/28/19 2:12 PM, Thomas Gleixner wrote:
> The 32bit variants of vdso_clock_gettime()/getres() have a NULL pointer
> check for the timespec pointer. That's inconsistent vs. 64bit.
> 
> But the vdso implementation will never be consistent versus the syscall
> because the only case which it can handle is NULL. Any other invalid
> pointer will cause a segfault. So special casing NULL is not really useful.
> 
> Remove it along with the superflouos syscall fallback invocation as that
> will return -EFAULT anyway. That also gets rid of the dubious typecast
> which only works because the pointer is NULL.

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@....com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@....com>

> 
> Fixes: 00b26474c2f1 ("lib/vdso: Provide generic VDSO implementation")
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  lib/vdso/gettimeofday.c |   18 ++----------------
>  1 file changed, 2 insertions(+), 16 deletions(-)
> 
> --- a/lib/vdso/gettimeofday.c
> +++ b/lib/vdso/gettimeofday.c
> @@ -115,9 +115,6 @@ static __maybe_unused int
>  	struct __kernel_timespec ts;
>  	int ret;
>  
> -	if (res == NULL)
> -		goto fallback;
> -
>  	ret = __cvdso_clock_gettime(clock, &ts);
>  
>  	if (ret == 0) {
> @@ -126,9 +123,6 @@ static __maybe_unused int
>  	}
>  
>  	return ret;
> -
> -fallback:
> -	return clock_gettime_fallback(clock, (struct __kernel_timespec *)res);
>  }
>  
>  static __maybe_unused int
> @@ -204,10 +198,8 @@ int __cvdso_clock_getres(clockid_t clock
>  		goto fallback;
>  	}
>  
> -	if (res) {
> -		res->tv_sec = 0;
> -		res->tv_nsec = ns;
> -	}
> +	res->tv_sec = 0;
> +	res->tv_nsec = ns;
>  
>  	return 0;
>  
> @@ -221,9 +213,6 @@ static __maybe_unused int
>  	struct __kernel_timespec ts;
>  	int ret;
>  
> -	if (res == NULL)
> -		goto fallback;
> -
>  	ret = __cvdso_clock_getres(clock, &ts);
>  
>  	if (ret == 0) {
> @@ -232,8 +221,5 @@ static __maybe_unused int
>  	}
>  
>  	return ret;
> -
> -fallback:
> -	return clock_getres_fallback(clock, (struct __kernel_timespec *)res);
>  }
>  #endif /* VDSO_HAS_CLOCK_GETRES */
> 
> 

-- 
Regards,
Vincenzo