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[209.85.220.65]) by mx.google.com with SMTPS id z5sor32426122ljc.29.2019.07.29.01.06.11 for (Google Transport Security); Mon, 29 Jul 2019 01:06:12 -0700 (PDT) Received-SPF: pass (google.com: domain of jrdr.linux@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b="LB/VimNW"; spf=pass (google.com: domain of jrdr.linux@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=jrdr.linux@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=q+5I/p/Nycgrz3gMKuzpkFKzO+GKwckGcbd0BiK6zG0=; b=LB/VimNWk6JAU5/0EApO5jynRztUXjN0TlosFKaq/kodUwFVw0PewLEs0V68CR581J 4JlwzGL1H/RgmulXJE0tUnfGIbnAg+sboDZsIgfwmu5zl5BuBomBD0GnsmCfvsD96P7c 81a3Itk5111vnbz+3jlZUj6HwRjk603ngMwMhwxGZtZyazLVFIh7gk8zwdo6uMokLrwo BxlrHYeLTM7lyQGhdhkpGxhnpuX6jxPYtIgh6+bxdTukqfk38gWfWBmqLnsQhkJfiAW1 gHJBp5gXUR/8JTLCOXBmIl6aYSDoYBFQWfAph63tY1YwjFkjyQjdiesYPJO7SBVp2XXA p9xQ== X-Google-Smtp-Source: APXvYqz0P76ouodZLQJ+67CUBUqcRzH9RJUfbxlKZqHe7C7pDJbANNDWcvHTrBJed/XvhfMm/hXZdRRCBXnmIBaGkUs= X-Received: by 2002:a2e:93cc:: with SMTP id p12mr57966349ljh.11.1564387571686; Mon, 29 Jul 2019 01:06:11 -0700 (PDT) MIME-Version: 1.0 References: <20190215024830.GA26477@jordon-HP-15-Notebook-PC> <20190728180611.GA20589@mail-itl> In-Reply-To: <20190728180611.GA20589@mail-itl> From: Souptick Joarder Date: Mon, 29 Jul 2019 13:35:59 +0530 Message-ID: Subject: Re: [Xen-devel] [PATCH v4 8/9] xen/gntdev.c: Convert to use vm_map_pages() To: =?UTF-8?Q?Marek_Marczykowski=2DG=C3=B3recki?= Cc: Andrew Morton , Matthew Wilcox , Michal Hocko , Boris Ostrovsky , Juergen Gross , Russell King - ARM Linux , robin.murphy@arm.com, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, Linux-MM Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Jul 28, 2019 at 11:36 PM Marek Marczykowski-G=C3=B3recki wrote: > > On Fri, Feb 15, 2019 at 08:18:31AM +0530, Souptick Joarder wrote: > > Convert to use vm_map_pages() to map range of kernel > > memory to user vma. > > > > map->count is passed to vm_map_pages() and internal API > > verify map->count against count ( count =3D vma_pages(vma)) > > for page array boundary overrun condition. > > This commit breaks gntdev driver. If vma->vm_pgoff > 0, vm_map_pages > will: > - use map->pages starting at vma->vm_pgoff instead of 0 The actual code ignores vma->vm_pgoff > 0 scenario and mapped the entire map->pages[i]. Why the entire map->pages[i] needs to be mapped if vma->vm_pgoff > 0 (in original code) ? are you referring to set vma->vm_pgoff =3D 0 irrespective of value passed from user space ? If yes, using vm_map_pages_zero() is an alternate option. > - verify map->count against vma_pages()+vma->vm_pgoff instead of just > vma_pages(). In original code -> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c index 559d4b7f807d..469dfbd6cf90 100644 --- a/drivers/xen/gntdev.c +++ b/drivers/xen/gntdev.c @@ -1084,7 +1084,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma) int index =3D vma->vm_pgoff; int count =3D vma_pages(vma); Count is user passed value. struct gntdev_grant_map *map; - int i, err =3D -EINVAL; + int err =3D -EINVAL; if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED)) return -EINVAL; @@ -1145,12 +1145,9 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma) goto out_put_map; if (!use_ptemod) { - for (i =3D 0; i < count; i++) { - err =3D vm_insert_page(vma, vma->vm_start + i*PAGE_SIZE, - map->pages[i]); and when count > i , we end up with trying to map memory outside boundary of map->pages[i], which was not correct. - if (err) - goto out_put_map; - } + err =3D vm_map_pages(vma, map->pages, map->count); + if (err) + goto out_put_map; With this commit, inside __vm_map_pages(), we have addressed this scenario. +static int __vm_map_pages(struct vm_area_struct *vma, struct page **pages, + unsigned long num, unsigned long offset) +{ + unsigned long count =3D vma_pages(vma); + unsigned long uaddr =3D vma->vm_start; + int ret, i; + + /* Fail if the user requested offset is beyond the end of the object */ + if (offset > num) + return -ENXIO; + + /* Fail if the user requested size exceeds available object size */ + if (count > num - offset) + return -ENXIO; By checking count > num -offset. (considering vma->vm_pgoff !=3D 0 as well)= . So we will never cross the boundary of map->pages[i]. > > In practice, this breaks using a single gntdev FD for mapping multiple > grants. How ? > > It looks like vm_map_pages() is not a good fit for this code and IMO it > should be reverted. Did you hit any issue around this code in real time ? > > > Signed-off-by: Souptick Joarder > > Reviewed-by: Boris Ostrovsky > > --- > > drivers/xen/gntdev.c | 11 ++++------- > > 1 file changed, 4 insertions(+), 7 deletions(-) > > > > diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c > > index 5efc5ee..5d64262 100644 > > --- a/drivers/xen/gntdev.c > > +++ b/drivers/xen/gntdev.c > > @@ -1084,7 +1084,7 @@ static int gntdev_mmap(struct file *flip, struct = vm_area_struct *vma) > > int index =3D vma->vm_pgoff; > > int count =3D vma_pages(vma); > > struct gntdev_grant_map *map; > > - int i, err =3D -EINVAL; > > + int err =3D -EINVAL; > > > > if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED)) > > return -EINVAL; > > @@ -1145,12 +1145,9 @@ static int gntdev_mmap(struct file *flip, struct= vm_area_struct *vma) > > goto out_put_map; > > > > if (!use_ptemod) { > > - for (i =3D 0; i < count; i++) { > > - err =3D vm_insert_page(vma, vma->vm_start + i*PAG= E_SIZE, > > - map->pages[i]); > > - if (err) > > - goto out_put_map; > > - } > > + err =3D vm_map_pages(vma, map->pages, map->count); > > + if (err) > > + goto out_put_map; > > } else { > > #ifdef CONFIG_X86 > > /* > > -- > Best Regards, > Marek Marczykowski-G=C3=B3recki > Invisible Things Lab > A: Because it messes up the order in which people normally read text. > Q: Why is top-posting such a bad thing?