From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: [PATCH] drivers/char/mem.c: Add /dev/ioports, supporting 16-bit and 32-bit ports Date: Fri, 09 May 2014 13:54:05 -0700 Message-ID: <536D406D.2080508@zytor.com> References: <20140509191914.GA7286@jtriplet-mobl1> <9233735.5FfZoZovqP@wuerfel> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <9233735.5FfZoZovqP@wuerfel> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Arnd Bergmann , Josh Triplett Cc: Greg Kroah-Hartman , akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-api@vger.kernel.org On 05/09/2014 12:58 PM, Arnd Bergmann wrote: > On Friday 09 May 2014 12:19:16 Josh Triplett wrote: > >> + if (!access_ok(VERIFY_WRITE, buf, count)) >> + return -EFAULT; >> + if (port > 65535) >> + return 0; > > This should probably test against IO_SPACE_LIMIT, which may be zero, > something larger than 65536 or even ULONG_MAX, depending on the > architecture. > > In cases where this IO_SPACE_LIMIT is zero or ULONG_MAX, we should > probably disallow access completely. The former case is for architectures > that don't have any I/O ports, the other is either a mistake, or is > used when inb is defined as readb, and the port numbers are just virtual > addresses. > PCI supports a 32-bit I/O address space, so if the architecture permits it, having a 32-bit I/O space is perfectly legitimate. It is worth noting that /dev/port has the same problem. However, if we're going to have these devices I'm wondering if having /dev/portw and /dev/portl (or something like that) might not make sense, rather than requiring a system call per transaction. Also, x86 supports unaligned I/O port references, but not all architectures do. On the other hand, x86 also supports ioperm(). -hpa