linux-kernel - Re: Kernel bug with MPX?

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Date:   Mon, 18 Mar 2019 12:47:03 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Richard Biener <rguenther@...e.de>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: Kernel bug with MPX?

On Thu 14-03-19 09:51:42, Dave Hansen wrote:
[...]
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> MPX is being removed from the kernel due to a lack of support
> in the toolchain going forward (gcc).
> 
> The first thing we need to do is remove the userspace-visible
> ABIs so that applications will stop using it.  The most visible
> one are the enable/disable prctl()s.  Remove them first.
> 
> This is the most minimal and least invasive patch needed to
> start removing MPX.

Is this something we _want_ to push to stable trees?
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> ---
> 
>  b/include/uapi/linux/prctl.h |    2 +-
>  b/kernel/sys.c               |   16 ++--------------
>  2 files changed, 3 insertions(+), 15 deletions(-)
> 
> diff -puN include/uapi/linux/prctl.h~mpx-remove-apis include/uapi/linux/prctl.h
> --- a/include/uapi/linux/prctl.h~mpx-remove-apis	2019-01-04 14:40:06.853514089 -0800
> +++ b/include/uapi/linux/prctl.h	2019-01-04 14:40:06.860514089 -0800
> @@ -181,7 +181,7 @@ struct prctl_mm_map {
>  #define PR_GET_THP_DISABLE	42
>  
>  /*
> - * Tell the kernel to start/stop helping userspace manage bounds tables.
> + * No longer implemented, but left here to ensure the numbers stay reserved:
>   */
>  #define PR_MPX_ENABLE_MANAGEMENT  43
>  #define PR_MPX_DISABLE_MANAGEMENT 44
> diff -puN kernel/sys.c~mpx-remove-apis kernel/sys.c
> --- a/kernel/sys.c~mpx-remove-apis	2019-01-04 14:40:06.857514089 -0800
> +++ b/kernel/sys.c	2019-01-04 14:40:06.860514089 -0800
> @@ -103,12 +103,6 @@
>  #ifndef SET_TSC_CTL
>  # define SET_TSC_CTL(a)		(-EINVAL)
>  #endif
> -#ifndef MPX_ENABLE_MANAGEMENT
> -# define MPX_ENABLE_MANAGEMENT()	(-EINVAL)
> -#endif
> -#ifndef MPX_DISABLE_MANAGEMENT
> -# define MPX_DISABLE_MANAGEMENT()	(-EINVAL)
> -#endif
>  #ifndef GET_FP_MODE
>  # define GET_FP_MODE(a)		(-EINVAL)
>  #endif
> @@ -2448,15 +2442,9 @@ SYSCALL_DEFINE5(prctl, int, option, unsi
>  		up_write(&me->mm->mmap_sem);
>  		break;
>  	case PR_MPX_ENABLE_MANAGEMENT:
> -		if (arg2 || arg3 || arg4 || arg5)
> -			return -EINVAL;
> -		error = MPX_ENABLE_MANAGEMENT();
> -		break;
>  	case PR_MPX_DISABLE_MANAGEMENT:
> -		if (arg2 || arg3 || arg4 || arg5)
> -			return -EINVAL;
> -		error = MPX_DISABLE_MANAGEMENT();
> -		break;
> +		/* No longer implemented: */
> +		return -EINVAL;
>  	case PR_SET_FP_MODE:
>  		error = SET_FP_MODE(me, arg2);
>  		break;
> _


-- 
Michal Hocko
SUSE Labs