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The existing code in emit_call on RV64 checks that the PC-relative offset to the function fits in 32 bits before calling emit_jump_and_link to emit an auipc+jalr pair. However, this check is incorrect because offsets in the range [2^31 - 2^11, 2^31 - 1] cannot be encoded using auipc+jalr on RV64 (see discussion [1]). The RISC-V spec has recently been updated to reflect this fact [2, 3]. This patch fixes the problem by moving the check on the offset into emit_jump_and_link and modifying it to the correct range of encodable offsets, which is [-2^31 - 2^11, 2^31 - 2^11). This also enforces the check on the offset to other uses of emit_jump_and_link (e.g., BPF_JA) as well. Currently, this bug is unlikely to be triggered, because the memory region from which JITed images are allocated is close enough to kernel text for the offsets to not become too large; and because the bounds on BPF program size are small enough. This patch prevents this problem from becoming an issue if either of these change. [1]: https://groups.google.com/a/groups.riscv.org/forum/#!topic/isa-dev/bwWFhBnnZFQ [2]:b1e42e09ac[3]:4c1b2066ebSigned-off-by: Luke Nelson <luke.r.nels@gmail.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20200406221604.18547-1-luke.r.nels@gmail.com
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.