a192103a11
s390x eBPF programs use the following extension to the s390x calling
convention: tail call counter is passed on stack at offset
STK_OFF_TCCNT, which callees otherwise use as scratch space.
Currently trampoline does not respect this and clobbers tail call
counter. This breaks enforcing tail call limits in eBPF programs, which
have trampolines attached to them.
Fix by forwarding a copy of the tail call counter to the original eBPF
program in the trampoline (for fexit), and by restoring it at the end
of the trampoline (for fentry).
Fixes: 528eb2cb87bc ("s390/bpf: Implement arch_prepare_bpf_trampoline()")
Reported-by: Leon Hwang <hffilwlqm@gmail.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230906004448.111674-1-iii@linux.ibm.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.