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[ Upstream commitb5e9ad522c] While the check_max_stack_depth function explores call chains emanating from the main prog, which is typically enough to cover all possible call chains, it doesn't explore those rooted at async callbacks unless the async callback will have been directly called, since unlike non-async callbacks it skips their instruction exploration as they don't contribute to stack depth. It could be the case that the async callback leads to a callchain which exceeds the stack depth, but this is never reachable while only exploring the entry point from main subprog. Hence, repeat the check for the main subprog *and* all async callbacks marked by the symbolic execution pass of the verifier, as execution of the program may begin at any of them. Consider functions with following stack depths: main: 256 async: 256 foo: 256 main: rX = async bpf_timer_set_callback(...) async: foo() Here, async is not descended as it does not contribute to stack depth of main (since it is referenced using bpf_pseudo_func and not bpf_pseudo_call). However, when async is invoked asynchronously, it will end up breaching the MAX_BPF_STACK limit by calling foo. Hence, in addition to main, we also need to explore call chains beginning at all async callback subprogs in a program. Fixes:7ddc80a476("bpf: Teach stack depth check about async callbacks.") Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Link: https://lore.kernel.org/r/20230717161530.1238-3-memxor@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
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.