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 for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20250918194556.3814405-1-clm@meta.com>
Date: Thu, 18 Sep 2025 12:45:38 -0700
From: Chris Mason <clm@...a.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
CC: Chris Mason <clm@...a.com>, Andrew Morton <akpm@...ux-foundation.org>,
        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>, Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v2 16/16] kcov: update kcov to use mmap_prepare

On Wed, 10 Sep 2025 21:22:11 +0100 Lorenzo Stoakes <lorenzo.stoakes@...cle.com> wrote:

> We can use the mmap insert pages functionality provided for use in
> mmap_prepare to insert the kcov pages as required.
> 
> This does necessitate an allocation, but since it's in the mmap path this
> doesn't seem egregious. The allocation/freeing of the pages array is
> handled automatically by vma_desc_set_mixedmap_pages() and the mapping
> logic.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> ---
>  kernel/kcov.c | 42 ++++++++++++++++++++++++++----------------
>  1 file changed, 26 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 1d85597057e1..2bcf403e5f6f 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -484,31 +484,41 @@ void kcov_task_exit(struct task_struct *t)
>  	kcov_put(kcov);
>  }
>  
> -static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
> +static int kcov_mmap_error(int err)
> +{
> +	pr_warn_once("kcov: vm_insert_page() failed\n");
> +	return err;
> +}
> +
> +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) {
>  		res = -EINVAL;
>  		goto exit;
>  	}
>  	spin_unlock_irqrestore(&kcov->lock, flags);
> -	vm_flags_set(vma, VM_DONTEXPAND);
> -	for (off = 0; off < size; off += PAGE_SIZE) {
> -		page = vmalloc_to_page(kcov->area + off);
> -		res = vm_insert_page(vma, vma->vm_start + off, page);
> -		if (res) {
> -			pr_warn_once("kcov: vm_insert_page() failed\n");
> -			return res;
> -		}
> -	}
> +
> +	desc->vm_flags |= VM_DONTEXPAND;
> +	nr_pages = size >> PAGE_SHIFT;
> +
> +	pages = mmap_action_mixedmap_pages(&desc->action, desc->start,
> +					   nr_pages);

Hi Lorenzo,

Not sure if it belongs here before the EINVAL tests, but it looks like
kcov->size doesn't have any page alignment.  I think size could be
4000 bytes other unaligned values, so nr_pages should round up.

-chris