Messages in this thread | | | Date | Thu, 24 Feb 2022 09:15:50 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH] binfmt_elf: Introduce KUnit test |
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On Wed, 23 Feb 2022 22:13:25 -0800 Kees Cook <keescook@chromium.org> wrote:
> Steven, I want to do fancy live-patch kind or things to replace functions, > but it doesn't need to be particularly fancy because KUnit tests (usually) > run single-threaded, etc. It looks like kprobes could almost do it, but > I don't see a way to have it _avoid_ making a function call.
// This is called just before the hijacked function is called static void notrace my_tramp(unsigned long ip, unsigned long parent_ip, struct ftrace_ops *ops, struct ftrace_regs *fregs) { int bit;
bit = ftrace_test_recursion_trylock(ip, parent_ip); if (WARN_ON_ONCE(bit < 0)) return;
/* * This uses the live kernel patching arch code to now return * to new_function() instead of the one that was called. * If you want to do a lookup, you can look at the "ip" * which will give you the function you are about to replace. * Note, it may not be equal to the function address, * but for that, you can have this: * ip = ftrace_location(function_ip); * which will give the ip that is passed here. */ klp_arch_set_pc(fregs, new_function);
ftrace_test_recursion_unlock(bit); }
static struct ftrace_ops my_ops = { .func = my_tramp; .flags = FTRACE_OPS_FL_IPMODIFY | #ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS FTRACE_OPS_FL_SAVE_REGS | #endif FTRACE_OPS_FL_DYNAMIC; };
// Assuming you know the function ip you want to hijack register_my_kutest_ip(unsigned long func_ip) { unsigned long ip; int ret;
ip = ftrace_location(func_ip); if (!ip) // not a ftrace function? return;
ret = ftrace_set_filter_ip(&my_ops, ip, 0, 0); if (ret < 0) return;
// you can register more than one ip if the last parameter // is zero (1 means to reset the list)
ret = register_ftrace_function(&my_ops); if (ret < 0) return; }
That's pretty much it. Note, I did not compile nor test the above, so there may be some mistakes.
For more information about how to use ftrace, see
Documentation/trace/ftrace-uses.rst
Which should probably get a section on how to do kernel patching.
-- Steve
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