On Friday 09 May 2014 13:54:05 H. Peter Anvin wrote: > 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. Right, but on all 32-bit architectures other than x86, the I/O ports are mapped into physical memory addresses, which means you can't map all of the I/O space into the CPU address space. On 64-bit architectures you can, but then it's UINT_MAX, not ULONG_MAX. There is also the theoretical case of machines mapping a window of I/O addresses with portnumber==phys_addr as we normally do for PCI memory space, but I haven't seen anyone actually do that. Practically every PCI implementation (if they have I/O space at all) maps a small number of ports (65536 or 1048576 mostly) starting at port number zero to a fixed physical CPU address. > It is worth noting that /dev/port has the same problem. Right. We should fix that, too. > 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. Actually the behavior of /dev/port for >1 byte writes seems questionable already: There are very few devices on which writing to consecutive port numbers makes sense. Normally you just want to write a series of bytes (or 16/32 bit words) into the same port number instead, as the outsb()/outsw()/outsl() functions do. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
