RE: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c"

[David Laight]

From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
> Sent: 22 October 2020 14:51

I've rammed the code into godbolt.

https://godbolt.org/z/9v5PPW

Definitely a clang bug.

Search for [wx]24 in the clang output.
nr_segs comes in as w2 and the initial bound checks are done on w2.
w24 is loaded from w2 - I don't believe this changes the high bits.
There are no references to w24, just x24.
So the kmalloc_array() is passed 'huge' and will fail.
The iov_iter_init also gets the 64bit value.

Note that the gcc code has a sign-extend copy of w2.

	David

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