linux-hardening - Re: [PATCH -next] mm: usercopy: add a debugfs interface to bypass the vmalloc check.

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: <Z09icnP7QuaLg4Qv@casper.infradead.org>
Date: Tue, 3 Dec 2024 19:56:34 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Uladzislau Rezki <urezki@...il.com>
Cc: Kefeng Wang <wangkefeng.wang@...wei.com>, zuoze <zuoze1@...wei.com>,
	gustavoars@...nel.org, akpm@...ux-foundation.org,
	linux-hardening@...r.kernel.org, linux-mm@...ck.org,
	keescook@...omium.org
Subject: Re: [PATCH -next] mm: usercopy: add a debugfs interface to bypass
 the vmalloc check.

On Tue, Dec 03, 2024 at 08:02:26PM +0100, Uladzislau Rezki wrote:

I think there are a few other things we can try here.

First, if the copy is small (and I still don't have an answer to that
...), we can skip the vmalloc lookup if the copy doesn't cross a page
boundary.

Second, we could try storing this in a maple tree rather than an rbtree.
That gives us RCU protected lookups rather than under a spinlock.

It might even be worth going to a rwlock first, in case the problem is
that there's severe lock contention.

But I've asked for data on spinlock contention and not received an
answer on that either, so I don't know what to suggest.

Anyway, NACK to the original patch; that's just a horrible idea.