Linux-api Archive on lore.kernel.org
 help / color / Atom feed
From: Michael Ellerman <mpe@ellerman.id.au>
To: Michal Hocko <mhocko@kernel.org>, linux-api@vger.kernel.org
Cc: Khalid Aziz <khalid.aziz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Russell King - ARM Linux <linux@armlinux.org.uk>,
	Andrea Arcangeli <aarcange@redhat.com>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	linux-arch@vger.kernel.org, Florian Weimer <fweimer@redhat.com>,
	John Hubbard <jhubbard@nvidia.com>,
	Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH 1/2] mm: introduce MAP_FIXED_SAFE
Date: Wed, 06 Dec 2017 16:15:24 +1100
Message-ID: <87tvx4e8sz.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <20171129144219.22867-2-mhocko@kernel.org>

Hi Michal,

Some comments below.

Michal Hocko <mhocko@kernel.org> writes:

> From: Michal Hocko <mhocko@suse.com>
>
> MAP_FIXED is used quite often to enforce mapping at the particular
> range. The main problem of this flag is, however, that it is inherently
> dangerous because it unmaps existing mappings covered by the requested
> range. This can cause silent memory corruptions. Some of them even with
> serious security implications. While the current semantic might be
> really desiderable in many cases there are others which would want to
> enforce the given range but rather see a failure than a silent memory
> corruption on a clashing range. Please note that there is no guarantee
> that a given range is obeyed by the mmap even when it is free - e.g.
> arch specific code is allowed to apply an alignment.

I don't think this last sentence is correct. Or maybe I don't understand
what you're referring to.

If you specifiy MAP_FIXED on a page boundary then the mapping must be
made at that address, I don't think arch code is allowed to add any
extra alignment.

> Introduce a new MAP_FIXED_SAFE flag for mmap to achieve this behavior.
> It has the same semantic as MAP_FIXED wrt. the given address request
> with a single exception that it fails with EEXIST if the requested
> address is already covered by an existing mapping. We still do rely on
> get_unmaped_area to handle all the arch specific MAP_FIXED treatment and
> check for a conflicting vma after it returns.
>
> [fail on clashing range with EEXIST as per Florian Weimer]
> [set MAP_FIXED before round_hint_to_min as per Khalid Aziz]
> Reviewed-by: Khalid Aziz <khalid.aziz@oracle.com>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
>  arch/alpha/include/uapi/asm/mman.h   |  2 ++
>  arch/mips/include/uapi/asm/mman.h    |  2 ++
>  arch/parisc/include/uapi/asm/mman.h  |  2 ++
>  arch/powerpc/include/uapi/asm/mman.h |  1 +
>  arch/sparc/include/uapi/asm/mman.h   |  1 +
>  arch/tile/include/uapi/asm/mman.h    |  1 +
>  arch/xtensa/include/uapi/asm/mman.h  |  2 ++
>  include/uapi/asm-generic/mman.h      |  1 +
>  mm/mmap.c                            | 11 +++++++++++
>  9 files changed, 23 insertions(+)
>
> diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h
> index 6bf730063e3f..ef3770262925 100644
> --- a/arch/alpha/include/uapi/asm/mman.h
> +++ b/arch/alpha/include/uapi/asm/mman.h
> @@ -32,6 +32,8 @@
>  #define MAP_STACK	0x80000		/* give out an address that is best suited for process/thread stacks */
>  #define MAP_HUGETLB	0x100000	/* create a huge page mapping */
>  
> +#define MAP_FIXED_SAFE	0x200000	/* MAP_FIXED which doesn't unmap underlying mapping */
> +

Why the new line before MAP_FIXED_SAFE? It should sit with the others.

You're using a different value to other arches here, but that's OK, and
alpha doesn't use asm-generic/mman.h or mman-common.h

> diff --git a/arch/powerpc/include/uapi/asm/mman.h b/arch/powerpc/include/uapi/asm/mman.h
> index e63bc37e33af..3ffd284e7160 100644
> --- a/arch/powerpc/include/uapi/asm/mman.h
> +++ b/arch/powerpc/include/uapi/asm/mman.h
> @@ -29,5 +29,6 @@
>  #define MAP_NONBLOCK	0x10000		/* do not block on IO */
>  #define MAP_STACK	0x20000		/* give out an address that is best suited for process/thread stacks */
>  #define MAP_HUGETLB	0x40000		/* create a huge page mapping */
> +#define MAP_FIXED_SAFE	0x800000	/* MAP_FIXED which doesn't unmap underlying mapping */

Why did you pick 0x800000?

I don't see any reason you can't use 0x8000 on powerpc.

 
> diff --git a/arch/sparc/include/uapi/asm/mman.h b/arch/sparc/include/uapi/asm/mman.h
> index 715a2c927e79..0c282c09fae8 100644
> --- a/arch/sparc/include/uapi/asm/mman.h
> +++ b/arch/sparc/include/uapi/asm/mman.h
> @@ -24,6 +24,7 @@
>  #define MAP_NONBLOCK	0x10000		/* do not block on IO */
>  #define MAP_STACK	0x20000		/* give out an address that is best suited for process/thread stacks */
>  #define MAP_HUGETLB	0x40000		/* create a huge page mapping */
> +#define MAP_FIXED_SAFE	0x80000		/* MAP_FIXED which doesn't unmap underlying mapping */

Using 0x80000 on sparc, sparc uses mman-common.h.

> diff --git a/arch/tile/include/uapi/asm/mman.h b/arch/tile/include/uapi/asm/mman.h
> index 9b7add95926b..b212f5fd5345 100644
> --- a/arch/tile/include/uapi/asm/mman.h
> +++ b/arch/tile/include/uapi/asm/mman.h
> @@ -30,6 +30,7 @@
>  #define MAP_DENYWRITE	0x0800		/* ETXTBSY */
>  #define MAP_EXECUTABLE	0x1000		/* mark it as an executable */
>  #define MAP_HUGETLB	0x4000		/* create a huge page mapping */
> +#define MAP_FIXED_SAFE	0x8000		/* MAP_FIXED which doesn't unmap underlying mapping */
  
That is the next free flag, but you could also use 0x80000 on tile.

tile uses mman-common.h.

> diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h
> index 2bfe590694fc..0daf199caa57 100644
> --- a/arch/xtensa/include/uapi/asm/mman.h
> +++ b/arch/xtensa/include/uapi/asm/mman.h
> @@ -56,6 +56,7 @@
>  #define MAP_NONBLOCK	0x20000		/* do not block on IO */
>  #define MAP_STACK	0x40000		/* give out an address that is best suited for process/thread stacks */
>  #define MAP_HUGETLB	0x80000		/* create a huge page mapping */
> +#define MAP_FIXED_SAFE	0x100000	/* MAP_FIXED which doesn't unmap underlying mapping */

xtensa doesn't use asm-generic/mman.h or mman-common.h

>  #ifdef CONFIG_MMAP_ALLOW_UNINITIALIZED
>  # define MAP_UNINITIALIZED 0x4000000	/* For anonymous mmap, memory could be
>  					 * uninitialized */
> @@ -63,6 +64,7 @@
>  # define MAP_UNINITIALIZED 0x0		/* Don't support this flag */
>  #endif
>  
> +

Stray new line.

>  /*
>   * Flags for msync
>   */
> diff --git a/include/uapi/asm-generic/mman.h b/include/uapi/asm-generic/mman.h
> index 2dffcbf705b3..56cde132a80a 100644
> --- a/include/uapi/asm-generic/mman.h
> +++ b/include/uapi/asm-generic/mman.h
> @@ -13,6 +13,7 @@
>  #define MAP_NONBLOCK	0x10000		/* do not block on IO */
>  #define MAP_STACK	0x20000		/* give out an address that is best suited for process/thread stacks */
>  #define MAP_HUGETLB	0x40000		/* create a huge page mapping */
> +#define MAP_FIXED_SAFE	0x80000		/* MAP_FIXED which doesn't unmap underlying mapping */

So I think I proved above that all the arches that are using 0x80000 are
also using mman-common.h, and vice-versa.

So you can put this in mman-common.h can't you?

> diff --git a/mm/mmap.c b/mm/mmap.c
> index 476e810cf100..e84339842bb8 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1342,6 +1342,10 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
>  		if (!(file && path_noexec(&file->f_path)))
>  			prot |= PROT_EXEC;
>  
> +	/* force arch specific MAP_FIXED handling in get_unmapped_area */
> +	if (flags & MAP_FIXED_SAFE)
> +		flags |= MAP_FIXED;
> +

The comment is misleading, because literally on the next line below we
check MAP_FIXED and change the behaviour, but not in the arch code.

>  	if (!(flags & MAP_FIXED))
>  		addr = round_hint_to_min(addr);

So it would be more accurate to say something like:

	/*
	 * Internal to the kernel MAP_FIXED_SAFE is a superset of
	 * MAP_FIXED, so set MAP_FIXED in flags if MAP_FIXED_SAFE was
	 * set by the caller. This avoids all the arch code having to
	 * check for MAP_FIXED and MAP_FIXED_SAFE.
	 */
	if (flags & MAP_FIXED_SAFE)
		flags |= MAP_FIXED;


cheers

  reply index

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-29 14:42 [PATCH 0/2] " Michal Hocko
2017-11-29 14:42 ` [PATCH 1/2] " Michal Hocko
2017-12-06  5:15   ` Michael Ellerman [this message]
2017-12-06  9:27     ` Michal Hocko
2017-12-06 10:02       ` Michal Hocko
2017-12-07 12:07   ` Pavel Machek
2017-11-29 14:42 ` [PATCH 2/2] fs, elf: drop MAP_FIXED usage from elf_map Michal Hocko
2017-11-29 17:45   ` Khalid Aziz
2017-11-29 14:45 ` [PATCH] mmap.2: document new MAP_FIXED_SAFE flag Michal Hocko
2017-11-30  3:16   ` John Hubbard
2017-11-30  8:23     ` Michal Hocko
2017-11-30  8:24   ` [PATCH v2] " Michal Hocko
2017-11-30 18:31     ` John Hubbard
2017-11-30 18:39       ` Michal Hocko
2017-11-29 15:13 ` [PATCH 0/2] mm: introduce MAP_FIXED_SAFE Rasmus Villemoes
     [not found]   ` <b154b794-7a8b-995e-0954-9234b9446b31-rjjw5hvvQKZaa/9Udqfwiw@public.gmane.org>
2017-11-29 15:50     ` Michal Hocko
2017-11-29 22:15   ` Kees Cook
2017-11-29 22:12 ` Kees Cook
2017-11-29 22:25 ` Kees Cook
     [not found]   ` <CAGXu5jLa=b2HhjWXXTQunaZuz11qUhm5aNXHpS26jVqb=G-gfw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-11-30  6:58     ` Michal Hocko
2017-12-01 15:26       ` Cyril Hrubis
2017-12-06  4:51         ` Michael Ellerman
2017-12-06  4:54           ` Matthew Wilcox
2017-12-06  7:03             ` Matthew Wilcox
2017-12-06  7:33               ` John Hubbard
     [not found]                 ` <5f4fc834-274a-b8f1-bda0-5bcddc5902ed-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2017-12-06  7:35                   ` Florian Weimer
2017-12-06  8:06                     ` John Hubbard
     [not found]                       ` <27ee1755-76d8-f086-5760-9c973b31108a-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2017-12-06  8:54                         ` Florian Weimer
     [not found]               ` <20171206070355.GA32044-PfSpb0PWhxZc2C7mugBRk2EX/6BAtgUQ@public.gmane.org>
2017-12-07  5:46                 ` Michael Ellerman
2017-12-07 19:14                   ` Kees Cook
     [not found]                     ` <CAGXu5jLWRQn6EaXEEvdvXr+4gbiJawwp1EaLMfYisHVfMiqgSA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-12-07 19:57                       ` Matthew Wilcox
2017-12-08  8:33                         ` Michal Hocko
     [not found]                           ` <20171208083315.GR20234-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org>
2017-12-08 20:13                             ` Kees Cook
     [not found]                               ` <CAGXu5j+VupGmKEEHx-uNXw27Xvndu=0ObsBqMwQiaYPyMGD+vw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-12-08 20:57                                 ` Matthew Wilcox
2017-12-08 11:08                         ` Michael Ellerman
2017-12-08 14:27                           ` Pavel Machek
2017-12-08 20:31                             ` Cyril Hrubis
2017-12-08 20:47                             ` Florian Weimer
2017-12-08 14:33                           ` David Laight
2017-12-06  4:50       ` Michael Ellerman
     [not found]         ` <87zi6we9z2.fsf-W0DJWXSxmBNbyGPkN3NxC2scP1bn1w/D@public.gmane.org>
2017-12-06  7:33           ` Rasmus Villemoes
     [not found]             ` <a3b3129a-2626-a65e-59b0-68aada523723-rjjw5hvvQKZaa/9Udqfwiw@public.gmane.org>
2017-12-06  9:08               ` Michal Hocko
2017-12-07  0:19                 ` Kees Cook
2017-12-07  1:08                   ` John Hubbard
2017-12-13  9:25 [PATCH v2 " Michal Hocko
2017-12-13  9:25 ` [PATCH 1/2] " Michal Hocko
     [not found]   ` <20171213092550.2774-2-mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2017-12-13 12:50     ` Matthew Wilcox
2017-12-13 13:01       ` Michal Hocko

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=87tvx4e8sz.fsf@concordia.ellerman.id.au \
    --to=mpe@ellerman.id.au \
    --cc=aarcange@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=fweimer@redhat.com \
    --cc=jhubbard@nvidia.com \
    --cc=khalid.aziz@oracle.com \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux@armlinux.org.uk \
    --cc=mhocko@kernel.org \
    --cc=mhocko@suse.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-api Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-api/0 linux-api/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-api linux-api/ https://lore.kernel.org/linux-api \
		linux-api@vger.kernel.org
	public-inbox-index linux-api

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-api


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git