From: Dave Chinner <david@fromorbit.com>
To: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Jason Gunthorpe <jgg@ziepe.ca>, Jens Axboe <axboe@kernel.dk>,
Matthew Wilcox <willy@infradead.org>,
Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>,
Leon Romanovsky <leon@kernel.org>,
Christian Benvenuti <benve@cisco.com>,
Nelson Escobar <neescoba@cisco.com>,
Bernard Metzler <bmt@zurich.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
Ian Rogers <irogers@google.com>,
Adrian Hunter <adrian.hunter@intel.com>,
Bjorn Topel <bjorn@kernel.org>,
Magnus Karlsson <magnus.karlsson@intel.com>,
Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
Jonathan Lemon <jonathan.lemon@gmail.com>,
"David S . Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Christian Brauner <brauner@kernel.org>,
Richard Cochran <richardcochran@gmail.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Jesper Dangaard Brouer <hawk@kernel.org>,
John Fastabend <john.fastabend@gmail.com>,
linux-fsdevel@vger.kernel.org, linux-perf-users@vger.kernel.org,
netdev@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH] mm/gup: disallow GUP writing to file-backed mappings by default
Date: Mon, 24 Apr 2023 08:29:41 +1000 [thread overview]
Message-ID: <20230423222941.GR447837@dread.disaster.area> (raw)
In-Reply-To: <f86dc089b460c80805e321747b0898fd1efe93d7.1682168199.git.lstoakes@gmail.com>
On Sat, Apr 22, 2023 at 02:37:05PM +0100, Lorenzo Stoakes wrote:
> +/*
> + * Writing to file-backed mappings using GUP is a fundamentally broken operation
> + * as kernel write access to GUP mappings may not adhere to the semantics
> + * expected by a file system.
> + *
> + * In most instances we disallow this broken behaviour, however there are some
> + * exceptions to this enforced here.
> + */
> +static inline bool can_write_file_mapping(struct vm_area_struct *vma,
> + unsigned long gup_flags)
> +{
> + struct file *file = vma->vm_file;
> +
> + /* If we aren't pinning then no problematic write can occur. */
> + if (!(gup_flags & (FOLL_GET | FOLL_PIN)))
> + return true;
> +
> + /* Special mappings should pose no problem. */
> + if (!file)
> + return true;
Ok...
> +
> + /* Has the caller explicitly indicated this case is acceptable? */
> + if (gup_flags & FOLL_ALLOW_BROKEN_FILE_MAPPING)
> + return true;
> +
> + /* shmem and hugetlb mappings do not have problematic semantics. */
> + return vma_is_shmem(vma) || is_file_hugepages(file);
> +}
This looks backwards. We only want the override to occur when the
target won't otherwise allow it. i.e. This should be:
if (vma_is_shmem(vma))
return true;
if (is_file_hugepages(vma)
return true;
/*
* Issue a warning only if we are allowing a write to a mapping
* that does not support what we are attempting to do functionality.
*/
if (WARN_ON_ONCE(gup_flags & FOLL_ALLOW_BROKEN_FILE_MAPPING))
return true;
return false;
i.e. we only want the warning to fire when the override is
triggered - indicating that the caller is actually using a file
mapping in a broken way, not when it is being used on
file/filesystem that actually supports file mappings in this way.
> static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
> {
> vm_flags_t vm_flags = vma->vm_flags;
> int write = (gup_flags & FOLL_WRITE);
> int foreign = (gup_flags & FOLL_REMOTE);
> + bool vma_anon = vma_is_anonymous(vma);
>
> if (vm_flags & (VM_IO | VM_PFNMAP))
> return -EFAULT;
>
> - if (gup_flags & FOLL_ANON && !vma_is_anonymous(vma))
> + if ((gup_flags & FOLL_ANON) && !vma_anon)
> return -EFAULT;
>
> if ((gup_flags & FOLL_LONGTERM) && vma_is_fsdax(vma))
> @@ -978,6 +1008,10 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
> return -EFAULT;
>
> if (write) {
> + if (!vma_anon &&
> + WARN_ON_ONCE(!can_write_file_mapping(vma, gup_flags)))
> + return -EFAULT;
Yeah, the warning definitely belongs in the check function when the
override triggers allow broken behaviour to proceed, not when we
disallow a write fault because the underlying file/filesystem does
not support the operation being attempted.
-Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2023-04-23 22:29 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-22 13:37 [PATCH] mm/gup: disallow GUP writing to file-backed mappings by default Lorenzo Stoakes
2023-04-23 0:46 ` Hillf Danton
2023-04-23 19:32 ` Simon Horman
2023-04-23 19:40 ` Lorenzo Stoakes
2023-04-23 20:02 ` Simon Horman
2023-04-23 22:29 ` Dave Chinner [this message]
2023-04-23 22:56 ` Lorenzo Stoakes
2023-04-24 17:49 ` Jason Gunthorpe
2023-04-24 3:41 ` Mika Penttilä
2023-04-24 6:51 ` Lorenzo Stoakes
2023-04-24 12:02 ` Kirill A. Shutemov
2023-04-24 12:31 ` Lorenzo Stoakes
2023-04-24 13:40 ` Kirill A. Shutemov
2023-04-24 17:59 ` Jason Gunthorpe
2023-04-24 16:09 ` Jan Kara
2023-04-24 16:22 ` Lorenzo Stoakes
2023-04-24 17:53 ` Jason Gunthorpe
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=20230423222941.GR447837@dread.disaster.area \
--to=david@fromorbit.com \
--cc=acme@kernel.org \
--cc=adrian.hunter@intel.com \
--cc=akpm@linux-foundation.org \
--cc=alexander.shishkin@linux.intel.com \
--cc=ast@kernel.org \
--cc=axboe@kernel.dk \
--cc=benve@cisco.com \
--cc=bjorn@kernel.org \
--cc=bmt@zurich.ibm.com \
--cc=bpf@vger.kernel.org \
--cc=brauner@kernel.org \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=dennis.dalessandro@cornelisnetworks.com \
--cc=edumazet@google.com \
--cc=hawk@kernel.org \
--cc=irogers@google.com \
--cc=jgg@ziepe.ca \
--cc=john.fastabend@gmail.com \
--cc=jolsa@kernel.org \
--cc=jonathan.lemon@gmail.com \
--cc=kuba@kernel.org \
--cc=leon@kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-perf-users@vger.kernel.org \
--cc=lstoakes@gmail.com \
--cc=maciej.fijalkowski@intel.com \
--cc=magnus.karlsson@intel.com \
--cc=mark.rutland@arm.com \
--cc=mingo@redhat.com \
--cc=namhyung@kernel.org \
--cc=neescoba@cisco.com \
--cc=netdev@vger.kernel.org \
--cc=pabeni@redhat.com \
--cc=peterz@infradead.org \
--cc=richardcochran@gmail.com \
--cc=willy@infradead.org \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).