linux-kernel - Re: [patch 4/5] x86/vdso/32: Use 32bit syscall fallback

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Message-ID: <3baf0efb-dcae-4953-66aa-06c5ee9fbdf7@arm.com>
Date:   Mon, 29 Jul 2019 12:23:03 +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 4/5] x86/vdso/32: Use 32bit syscall fallback

On 28/07/2019 14:12, Thomas Gleixner wrote:
> The generic VDSO implementation uses the Y2038 safe clock_gettime64() and
> clock_getres_time64() syscalls as fallback for 32bit VDSO. This breaks
> seccomp setups because these syscalls might be not (yet) allowed.
> 
> Implement the 32bit variants which use the legacy syscalls and select the
> variant in the core library.
> 
> The 64bit time variants are not removed because they are required for the
> time64 based vdso accessors.
>

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

> Reported-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Reported-by: Paul Bolle <pebolle@...cali.nl>
> Suggested-by: Andy Lutomirski <luto@...nel.org>
> Fixes: 7ac870747988 ("x86/vdso: Switch to generic vDSO implementation")
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  arch/x86/include/asm/vdso/gettimeofday.h |   36 +++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> --- a/arch/x86/include/asm/vdso/gettimeofday.h
> +++ b/arch/x86/include/asm/vdso/gettimeofday.h
> @@ -96,6 +96,8 @@ long clock_getres_fallback(clockid_t _cl
>  
>  #else
>  
> +#define VDSO_HAS_32BIT_FALLBACK	1
> +
>  static __always_inline
>  long clock_gettime_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
>  {
> @@ -114,6 +116,23 @@ long clock_gettime_fallback(clockid_t _c
>  }
>  
>  static __always_inline
> +long clock_gettime32_fallback(clockid_t _clkid, struct old_timespec32 *_ts)
> +{
> +	long ret;
> +
> +	asm (
> +		"mov %%ebx, %%edx \n"
> +		"mov %[clock], %%ebx \n"
> +		"call __kernel_vsyscall \n"
> +		"mov %%edx, %%ebx \n"
> +		: "=a" (ret), "=m" (*_ts)
> +		: "0" (__NR_clock_gettime), [clock] "g" (_clkid), "c" (_ts)
> +		: "edx");
> +
> +	return ret;
> +}
> +
> +static __always_inline
>  long gettimeofday_fallback(struct __kernel_old_timeval *_tv,
>  			   struct timezone *_tz)
>  {
> @@ -146,6 +165,23 @@ clock_getres_fallback(clockid_t _clkid,
>  		: "edx");
>  
>  	return ret;
> +}
> +
> +static __always_inline
> +long clock_getres32_fallback(clockid_t _clkid, struct old_timespec32 *_ts)
> +{
> +	long ret;
> +
> +	asm (
> +		"mov %%ebx, %%edx \n"
> +		"mov %[clock], %%ebx \n"
> +		"call __kernel_vsyscall \n"
> +		"mov %%edx, %%ebx \n"
> +		: "=a" (ret), "=m" (*_ts)
> +		: "0" (__NR_clock_getres), [clock] "g" (_clkid), "c" (_ts)
> +		: "edx");
> +
> +	return ret;
>  }
>  
>  #endif
> 
> 

-- 
Regards,
Vincenzo