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SubjectRe: [PATCH] kprobes: Mark ftrace mcount handler functions nokprobe
On Mon, 19 Sep 2022 16:45:33 +0800
Liao Chang <liaochang1@huawei.com> wrote:

> Mark ftrace mcount handler functions nokprobe since probing on these
> functions probably reaches mcount recursivly during kprobe breakpoint
> handler for some architecture(tested for riscv, arm64), and reenter
> kprobe is treated as a fatal error, causes kernel panic.

This looks to me that the affected archs should be made more robust for this
case than to add this to the generic code.

-- Steve


>
> Pesudo code below demonstrate this problem:
>
> mcount
> function_trace_call (probed)
> arch_breakpoint_handler
> arch_setup_singlestep [mcount]
> function_trace_call (probed)
> arch_breakpoint_handler
> reenter_kprobe
> BUG
>
> Signed-off-by: Liao Chang <liaochang1@huawei.com>
> ---
> kernel/trace/trace_functions.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
> index 9f1bfbe105e8..440a678a8c7c 100644
> --- a/kernel/trace/trace_functions.c
> +++ b/kernel/trace/trace_functions.c
> @@ -16,6 +16,7 @@
> #include <linux/ftrace.h>
> #include <linux/slab.h>
> #include <linux/fs.h>
> +#include <linux/kprobes.h>
>
> #include "trace.h"
>
> @@ -194,6 +195,7 @@ function_trace_call(unsigned long ip, unsigned long parent_ip,
>
> ftrace_test_recursion_unlock(bit);
> }
> +NOKPROBE_SYMBOL(function_trace_call);
>
> #ifdef CONFIG_UNWINDER_ORC
> /*
> @@ -245,6 +247,7 @@ function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
> atomic_dec(&data->disabled);
> local_irq_restore(flags);
> }
> +NOKPROBE_SYMBOL(function_stack_trace_call);
>
> static inline bool is_repeat_check(struct trace_array *tr,
> struct trace_func_repeats *last_info,
> @@ -321,6 +324,7 @@ function_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
> out:
> ftrace_test_recursion_unlock(bit);
> }
> +NOKPROBE_SYMBOL(function_no_repeats_trace_call);
>
> static void
> function_stack_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
> @@ -363,6 +367,7 @@ function_stack_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
> atomic_dec(&data->disabled);
> local_irq_restore(flags);
> }
> +NOKPROBE_SYMBOL(function_stack_no_repeats_trace_call);
>
> static struct tracer_opt func_opts[] = {
> #ifdef CONFIG_STACKTRACE

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