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From: Arnd Bergmann <arnd@arndb.de>
To: afzal mohammed <afzal.mohd.ma@gmail.com>
Cc: Russell King <linux@armlinux.org.uk>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: ARM: vmsplit 4g/4g
Date: Mon, 8 Jun 2020 16:43:57 +0200	[thread overview]
Message-ID: <CAK8P3a1q51=_DUS1A8k67c3TyQ+7LTpeo98LmzoFK=qg+8Fktw@mail.gmail.com> (raw)
In-Reply-To: <20200608111834.GB5736@afzalpc>

On Mon, Jun 8, 2020 at 1:18 PM afzal mohammed <afzal.mohd.ma@gmail.com> wrote:
> On Sun, Jun 07, 2020 at 09:26:26PM +0200, Arnd Bergmann wrote:
>
> > I think you have to use get_user_pages() though instead of
> > get_user_pages_fast(),
> > in order to be able to check the permission bits to prevent doing a
> > copy_to_user()
> > into read-only mappings.
>
> i was not aware of this, is it documented somewhere ?, afaiu,
> difference b/n get_user_pages_fast() & get_user_pages() is that fast
> version will try to pin pages w/o acquiring mmap_sem if possible.

There is another difference: get_user_pages_fast() does not return
a  vm_area_struct pointer, which is where you would check the access
permissions. I suppose those pointers could not be returned to callers
that don't already hold the mmap_sem.

> > Do you want me to review the uaccess patch to look for any missing
> > corner cases, or do you want to do the whole set of user access helpers
> > first?
>
> i will cleanup and probably post RFC initially for the changes
> handling copy_{from,to}_user() to get feedback.

Ok.

      Arnd

  reply	other threads:[~2020-06-08 14:44 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-31  9:32 [PATCH 0/3] Highmem support for 32-bit RISC-V Eric Lin
2020-03-31  9:32 ` [PATCH 1/3] riscv/mm: Add pkmap region and CONFIG_HIGHMEM Eric Lin
2020-03-31  9:32 ` [PATCH 2/3] riscv/mm: Implement kmap() and kmap_atomic() Eric Lin
2020-03-31  9:32 ` [PATCH 3/3] riscv/mm: Add pkmap in print_vm_layout() Eric Lin
2020-04-02  9:31 ` [PATCH 0/3] Highmem support for 32-bit RISC-V Arnd Bergmann
2020-04-08  3:51   ` Alan Kao
2020-04-08 14:40     ` Arnd Bergmann
2020-04-14 15:17       ` afzal mohammed
2020-04-14 19:29         ` Arnd Bergmann
2020-04-15 13:54           ` afzal mohammed
2020-05-03 14:50             ` afzal mohammed
2020-05-03 20:20               ` Arnd Bergmann
2020-05-04  9:10                 ` afzal mohammed
2020-05-04 11:27                   ` Arnd Bergmann
2020-05-11 14:21                     ` ARM: static kernel in vmalloc space (was Re: [PATCH 0/3] Highmem support for 32-bit RISC-V) afzal mohammed
2020-05-11 15:29                       ` Arnd Bergmann
2020-05-12 10:47                         ` ARM: static kernel in vmalloc space afzal mohammed
2020-05-12 19:49                           ` Arnd Bergmann
2020-05-14 11:17                             ` afzal mohammed
2020-05-14 12:41                               ` Arnd Bergmann
2020-05-14 13:35                                 ` afzal mohammed
2020-05-14 14:44                                   ` afzal mohammed
2020-05-14 15:32                                   ` Arnd Bergmann
2020-05-16  6:06                                     ` afzal mohammed
2020-05-16  7:35                                       ` Arnd Bergmann
2020-06-07 12:59                                         ` ARM: vmsplit 4g/4g afzal mohammed
2020-06-07 16:11                                           ` Russell King - ARM Linux admin
2020-06-08 11:09                                             ` afzal mohammed
2020-06-10 10:10                                               ` Linus Walleij
2020-06-12 10:25                                                 ` afzal mohammed
2020-06-15  9:11                                                   ` Linus Walleij
2020-06-15 10:01                                                     ` afzal mohammed
2020-06-07 19:26                                           ` Arnd Bergmann
2020-06-08 11:18                                             ` afzal mohammed
2020-06-08 14:43                                               ` Arnd Bergmann [this message]
2020-06-08 15:17                                                 ` afzal mohammed
2020-06-09 12:15                                                   ` afzal mohammed
2020-06-09 14:22                                                     ` Arnd Bergmann
2020-05-14 16:25                                 ` ARM: static kernel in vmalloc space Russell King - ARM Linux admin
2020-05-14 21:12                                   ` Arnd Bergmann
2020-05-14 23:40                                     ` Russell King - ARM Linux admin
2020-05-15 15:41                                       ` Arnd Bergmann
2020-07-30  9:33                                         ` Linus Walleij
2020-07-30 10:17                                           ` Arnd Bergmann

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