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Commit31fd85816d("bpf: permits narrower load from bpf program context fields") made the verifier add AND instructions to clear the unwanted bits with a mask when doing a narrow load. The mask is computed with (1 << size * 8) - 1 where "size" is the size of the narrow load. When doing a 4 byte load of a an 8 byte field the verifier shifts the literal 1 by 32 places to the left. This results in an overflow of a signed integer, which is an undefined behavior. Typically, the computed mask was zero, so the result of the narrow load ended up being zero too. Cast the literal to long long to avoid overflows. Note that narrow load of the 4 byte fields does not have the undefined behavior, because the load size can only be either 1 or 2 bytes, so shifting 1 by 8 or 16 places will not overflow it. And reading 4 bytes would not be a narrow load of a 4 bytes field. Fixes:31fd85816d("bpf: permits narrower load from bpf program context fields") Reviewed-by: Alban Crequy <alban@kinvolk.io> Reviewed-by: Iago López Galeiras <iago@kinvolk.io> Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.io> Cc: Yonghong Song <yhs@fb.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.