Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH v3 2/4] x86/microcode: Fix __user annotations around generic_load_microcode() | Date | Tue, 2 Apr 2019 09:55:43 +0000 |
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From: Jann Horn > Sent: 01 April 2019 18:54 ... > > This ->get_ucode_data() BIOS-code-like contraption has always bugged me > > for being too ugly to live. > > > > How about we vmalloc() a properly sized buffer - both > > generic_load_microcode() callers have the size - and then hand that > > buffer into generic_load_microcode() ? > > > > That solves the __user annotation fun immediately and would simplify > > generic_load_microcode() additionally. > > > > The disadvantage would be having to vmalloc() a couple of... , I think > > it is megabytes, with that old loading method request_microcode_user() > > but then if vmalloc() fails, then it was clearly too big. I don't think > > the blob can ever be that big though, to fail vmalloc(), but I'm not > > going to bet on it... > > Hm. request_microcode_fw() gets that buffer from > request_firmware_direct(), which does this: > > __module_get(THIS_MODULE); > ret = _request_firmware(firmware_p, name, device, NULL, 0, > FW_OPT_UEVENT | FW_OPT_NO_WARN | > FW_OPT_NOFALLBACK); > module_put(THIS_MODULE); > return ret; > > What is that module_get()/module_put() supposed to be good for? Are we > expecting that caller to do something ridiculous like calling > module_put() on us? This doesn't seem to make any sense.
At least it isn't doing a try_module_get(THIS_MODULE) :-)
> And then _request_firmware() goes and ends up in places like > kernel_read_file(), which already use vmalloc(). > > > Anyway, isn't this kind of thing exactly why we have that iov_iter > stuff? request_microcode_fw() can build an ITER_KVEC, > request_microcode_user() can build an ITER_IOVEC. And then > generic_load_microcode() can use something like copy_from_iter(). Does > that sound reasonable?
That ought to allow the microcode be copied in chunks - removing the need for a massive buffer?
The largest file we ever copy to PCIe cards is a 6MB fpga image. But we do that by mmapping the PCIe registers directly into userspace.
David
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