From: "Theodore Ts'o" <tytso@mit.edu>
To: "Richard B. Johnson" <linux-os@analogic.com>
Cc: Hacksaw <hacksaw@hacksaw.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Tomko <tomko@haha.com>,
Linux Kernel list <linux-kernel@vger.kernel.org>
Subject: Re: Why system call need to copy the date from the userspace before using it
Date: Wed, 13 Apr 2005 14:37:43 -0400 [thread overview]
Message-ID: <20050413183742.GA5252@thunk.org> (raw)
In-Reply-To: <Pine.LNX.4.61.0504130818300.12518@chaos.analogic.com>
On Wed, Apr 13, 2005 at 08:40:05AM -0400, Richard B. Johnson wrote:
> The kernel does NOT have to copy data from user-space before
> using it.
Incorrect. It must, or the kernel code in question is by definition
buggy.
> In fact, user-mode pointers are valid in kernel-space
> when the kernel is performing a function on behalf of the user-
> mode code.
On some architectures, this is true. But not all architectures, and
not in all circumstances. For example, even on the x86 architecture,
in the 4G/4G mode, a user-mode pointer is *not* valid when kernel code
is running. You must use copy_to_user()/copy_from_user(). Simply
dereferencing a user-mode pointer is a BUG. It might work sometimes,
on some architectures, but not everywhere. Therefore, for correctly
written kernel code, you must not do it.
- Ted
next prev parent reply other threads:[~2005-04-13 18:39 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-04-13 4:21 Why system call need to copy the date from the userspace before using it Tomko
2005-04-13 5:30 ` Vadim Lobanov
2005-04-13 10:29 ` Jan-Benedict Glaw
2005-04-13 10:43 ` Tomko
2005-04-13 11:10 ` Catalin Marinas
2005-04-14 2:10 ` Tomko
2005-04-14 2:18 ` David Schwartz
2005-04-14 14:05 ` Helge Hafting
2005-04-13 11:33 ` Benjamin Herrenschmidt
2005-04-13 11:59 ` Hacksaw
2005-04-13 12:40 ` Richard B. Johnson
2005-04-13 18:37 ` Theodore Ts'o [this message]
2005-04-13 19:20 ` Richard B. Johnson
2005-04-16 4:50 ` Hacksaw
2005-04-16 5:18 ` Vadim Lobanov
2005-04-16 8:30 ` Hacksaw
2005-04-16 19:35 ` Vadim Lobanov
2005-04-16 23:46 ` David Wagner
-- strict thread matches above, loose matches on Subject: below --
2005-04-13 6:48 Vadim Lobanov
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