linux-kernel - Re: [PATCH v2 16/16] kcov: update kcov to use mmap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250915121617.GD1024672@nvidia.com>
Date: Mon, 15 Sep 2025 09:16:17 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Matthew Wilcox <willy@...radead.org>, Guo Ren <guoren@...nel.org>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	"David S . Miller" <davem@...emloft.net>,
	Andreas Larsson <andreas@...sler.com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Dave Jiang <dave.jiang@...el.com>, Nicolas Pitre <nico@...xnic.net>,
	Muchun Song <muchun.song@...ux.dev>,
	Oscar Salvador <osalvador@...e.de>,
	David Hildenbrand <david@...hat.com>,
	Konstantin Komarov <almaz.alexandrovich@...agon-software.com>,
	Baoquan He <bhe@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
	Dave Young <dyoung@...hat.com>, Tony Luck <tony.luck@...el.com>,
	Reinette Chatre <reinette.chatre@...el.com>,
	Dave Martin <Dave.Martin@....com>,
	James Morse <james.morse@....com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>, Hugh Dickins <hughd@...gle.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Uladzislau Rezki <urezki@...il.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-csky@...r.kernel.org,
	linux-mips@...r.kernel.org, linux-s390@...r.kernel.org,
	sparclinux@...r.kernel.org, nvdimm@...ts.linux.dev,
	linux-cxl@...r.kernel.org, linux-mm@...ck.org,
	ntfs3@...ts.linux.dev, kexec@...ts.infradead.org,
	kasan-dev@...glegroups.com
Subject: Re: [PATCH v2 16/16] kcov: update kcov to use mmap_prepare

On Wed, Sep 10, 2025 at 09:22:11PM +0100, Lorenzo Stoakes wrote:
> +static int kcov_mmap_prepare(struct vm_area_desc *desc)
>  {
>  	int res = 0;
> -	struct kcov *kcov = vma->vm_file->private_data;
> -	unsigned long size, off;
> -	struct page *page;
> +	struct kcov *kcov = desc->file->private_data;
> +	unsigned long size, nr_pages, i;
> +	struct page **pages;
>  	unsigned long flags;
>  
>  	spin_lock_irqsave(&kcov->lock, flags);
>  	size = kcov->size * sizeof(unsigned long);
> -	if (kcov->area == NULL || vma->vm_pgoff != 0 ||
> -	    vma->vm_end - vma->vm_start != size) {
> +	if (kcov->area == NULL || desc->pgoff != 0 ||
> +	    vma_desc_size(desc) != size) {

IMHO these range checks should be cleaned up into a helper:

/* Returns true if the VMA falls within starting_pgoff to
     starting_pgoff + ROUND_DOWN(length_bytes, PAGE_SIZE))
   Is careful to avoid any arithmetic overflow.
 */
vma_desc_check_range(desc, starting_pgoff=0, length_bytes=size);

> +	desc->vm_flags |= VM_DONTEXPAND;
> +	nr_pages = size >> PAGE_SHIFT;
> +
> +	pages = mmap_action_mixedmap_pages(&desc->action, desc->start,
> +					   nr_pages);
> +	if (!pages)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < nr_pages; i++)
> +		pages[i] = vmalloc_to_page(kcov->area + i * PAGE_SIZE);

This is not a mixed map.

All the memory comes from vmalloc_user() which makes them normal
struct pages with refcounts.

If anything the action should be called mmap_action_vmalloc_user() to
match how the memory was allocated instead of open coding something.

Jason