linux-kernel - Re: [RFC PATCH 5/5] mm: introduce MADV

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Date:   Tue, 28 Jul 2020 16:22:40 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Anthony Yznaga <anthony.yznaga@...cle.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-arch@...r.kernel.org
Cc:     mhocko@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org, arnd@...db.de,
        ebiederm@...ssion.com, keescook@...omium.org, gerg@...ux-m68k.org,
        christian.brauner@...ntu.com, peterz@...radead.org,
        esyr@...hat.com, jgg@...pe.ca, christian@...lner.me,
        areber@...hat.com, cyphar@...har.com, steven.sistare@...cle.com
Subject: Re: [RFC PATCH 5/5] mm: introduce MADV_DOEXEC

On 27.07.2020 20:11, Anthony Yznaga wrote:
> madvise MADV_DOEXEC preserves a memory range across exec.  Initially
> only supported for non-executable, non-stack, anonymous memory.
> MADV_DONTEXEC reverts the effect of a previous MADV_DOXEXEC call and
> undoes the preservation of the range.  After a successful exec call,
> the behavior of all ranges reverts to MADV_DONTEXEC.
> 
> Signed-off-by: Steve Sistare <steven.sistare@...cle.com>
> Signed-off-by: Anthony Yznaga <anthony.yznaga@...cle.com>
> ---
>  include/uapi/asm-generic/mman-common.h |  3 +++
>  mm/madvise.c                           | 25 +++++++++++++++++++++++++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
> index f94f65d429be..7c5f616b28f7 100644
> --- a/include/uapi/asm-generic/mman-common.h
> +++ b/include/uapi/asm-generic/mman-common.h
> @@ -72,6 +72,9 @@
>  #define MADV_COLD	20		/* deactivate these pages */
>  #define MADV_PAGEOUT	21		/* reclaim these pages */
>  
> +#define MADV_DOEXEC	22		/* do inherit across exec */
> +#define MADV_DONTEXEC	23		/* don't inherit across exec */
> +
>  /* compatibility flags */
>  #define MAP_FILE	0
>  
> diff --git a/mm/madvise.c b/mm/madvise.c
> index dd1d43cf026d..b447fa748649 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -103,6 +103,26 @@ static long madvise_behavior(struct vm_area_struct *vma,
>  	case MADV_KEEPONFORK:
>  		new_flags &= ~VM_WIPEONFORK;
>  		break;
> +	case MADV_DOEXEC:

For me MADV_KEEPONEXEC sounds better as it's symmetric to MADV_KEEPONFORK.

> +		/*
> +		 * MADV_DOEXEC is only supported on private, non-executable,
> +		 * non-stack anonymous memory and if the VM_EXEC_KEEP flag
> +		 * is available.
> +		 */
> +		if (!VM_EXEC_KEEP || vma->vm_file || vma->vm_flags & (VM_EXEC|VM_SHARED|VM_STACK)) {
> +			error = -EINVAL;
> +			goto out;
> +		}
> +		new_flags |= (new_flags & ~VM_MAYEXEC) | VM_EXEC_KEEP;
> +		break;
> +	case MADV_DONTEXEC:
> +		if (!VM_EXEC_KEEP) {
> +			error = -EINVAL;
> +			goto out;
> +		}
> +		if (new_flags & VM_EXEC_KEEP)
> +			new_flags |= (new_flags & ~VM_EXEC_KEEP) | VM_MAYEXEC;
> +		break;
>  	case MADV_DONTDUMP:
>  		new_flags |= VM_DONTDUMP;
>  		break;
> @@ -983,6 +1003,8 @@ static int madvise_inject_error(int behavior,
>  	case MADV_SOFT_OFFLINE:
>  	case MADV_HWPOISON:
>  #endif
> +	case MADV_DOEXEC:
> +	case MADV_DONTEXEC:
>  		return true;
>  
>  	default:
> @@ -1037,6 +1059,9 @@ static int madvise_inject_error(int behavior,
>   *  MADV_DONTDUMP - the application wants to prevent pages in the given range
>   *		from being included in its core dump.
>   *  MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump.
> + *  MADV_DOEXEC - On exec, preserve and duplicate this area in the new process
> + *		  if the new process allows it.
> + *  MADV_DONTEXEC - Undo the effect of MADV_DOEXEC.
>   *
>   * return values:
>   *  zero    - success
>