From cc252bb592638e0f7aea40d580186c36d89526b8 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 11 Dec 2024 13:53:35 -0500 Subject: fgraph: Still initialize idle shadow stacks when starting A bug was discovered where the idle shadow stacks were not initialized for offline CPUs when starting function graph tracer, and when they came online they were not traced due to the missing shadow stack. To fix this, the idle task shadow stack initialization was moved to using the CPU hotplug callbacks. But it removed the initialization when the function graph was enabled. The problem here is that the hotplug callbacks are called when the CPUs come online, but the idle shadow stack initialization only happens if function graph is currently active. This caused the online CPUs to not get their shadow stack initialized. The idle shadow stack initialization still needs to be done when the function graph is registered, as they will not be allocated if function graph is not registered. Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Link: https://lore.kernel.org/20241211135335.094ba282@batman.local.home Fixes: 2c02f7375e65 ("fgraph: Use CPU hotplug mechanism to initialize idle shadow stacks") Reported-by: Linus Walleij Tested-by: Linus Walleij Closes: https://lore.kernel.org/all/CACRpkdaTBrHwRbbrphVy-=SeDz6MSsXhTKypOtLrTQ+DgGAOcQ@mail.gmail.com/ Signed-off-by: Steven Rostedt (Google) --- kernel/trace/fgraph.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'kernel/trace/fgraph.c') diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c index 0bf78517b5d4..ddedcb50917f 100644 --- a/kernel/trace/fgraph.c +++ b/kernel/trace/fgraph.c @@ -1215,7 +1215,7 @@ void fgraph_update_pid_func(void) static int start_graph_tracing(void) { unsigned long **ret_stack_list; - int ret; + int ret, cpu; ret_stack_list = kcalloc(FTRACE_RETSTACK_ALLOC_SIZE, sizeof(*ret_stack_list), GFP_KERNEL); @@ -1223,6 +1223,12 @@ static int start_graph_tracing(void) if (!ret_stack_list) return -ENOMEM; + /* The cpu_boot init_task->ret_stack will never be freed */ + for_each_online_cpu(cpu) { + if (!idle_task(cpu)->ret_stack) + ftrace_graph_init_idle_task(idle_task(cpu), cpu); + } + do { ret = alloc_retstack_tasklist(ret_stack_list); } while (ret == -EAGAIN); -- cgit v1.2.3 From d65474033740ded0a4fe9a097fce72328655b41d Mon Sep 17 00:00:00 2001 From: Zilin Guan Date: Tue, 31 Dec 2024 11:37:31 +0000 Subject: fgraph: Add READ_ONCE() when accessing fgraph_array[] In __ftrace_return_to_handler(), a loop iterates over the fgraph_array[] elements, which are fgraph_ops. The loop checks if an element is a fgraph_stub to prevent using a fgraph_stub afterward. However, if the compiler reloads fgraph_array[] after this check, it might race with an update to fgraph_array[] that introduces a fgraph_stub. This could result in the stub being processed, but the stub contains a null "func_hash" field, leading to a NULL pointer dereference. To ensure that the gops compared against the fgraph_stub matches the gops processed later, add a READ_ONCE(). A similar patch appears in commit 63a8dfb ("function_graph: Add READ_ONCE() when accessing fgraph_array[]"). Cc: stable@vger.kernel.org Fixes: 37238abe3cb47 ("ftrace/function_graph: Pass fgraph_ops to function graph callbacks") Link: https://lore.kernel.org/20241231113731.277668-1-zilin@seu.edu.cn Signed-off-by: Zilin Guan Signed-off-by: Steven Rostedt (Google) --- kernel/trace/fgraph.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/trace/fgraph.c') diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c index ddedcb50917f..30e3ddc8a8a8 100644 --- a/kernel/trace/fgraph.c +++ b/kernel/trace/fgraph.c @@ -833,7 +833,7 @@ static unsigned long __ftrace_return_to_handler(struct fgraph_ret_regs *ret_regs #endif { for_each_set_bit(i, &bitmap, sizeof(bitmap) * BITS_PER_BYTE) { - struct fgraph_ops *gops = fgraph_array[i]; + struct fgraph_ops *gops = READ_ONCE(fgraph_array[i]); if (gops == &fgraph_stub) continue; -- cgit v1.2.3