Re: [PATCH v2 1/2] kprobes: introduce ARCH_HANDLES_KPROBES_ON_FTRACE

Masami Hiramatsu
2014-10-21T03:49:34Z

(2014/10/20 19:59), Heiko Carstens wrote:
> Allow architectures to implement handling of kprobes on function
> tracer call sites on their own, without depending on common code.
>
> This patch removes the kprobes check if a kprobe is being placed
> on a function tracer call site and therefore gives full responsibility
> of handling this correctly to the architecture.
>
> This patch also introduces a user space visible change: if a kprobe
> is placed into the middle of an ftrace instruction the return value
> is changed from -EINVAL to -EILSEQ also for architectures which do
> not support KPROBES_ON_FTRACE.
> However in reality this change shouldn't matter at all.

Could you try to remove new kconfig by using a weak function?
This could be done with below functions:

In kernel/kprobes.c:

int __weak arch_check_ftrace_location(struct kprobe *p)
{
unsigned long ftrace_addr = ftrace_location((unsigned long)p->addr);
if (ftrace_addr) {
...
}

And in arch/s390/kernel/kprobes.c:
int arch_check_ftrace_location(struct kprobe *p)
{
return 0;
}

And in include/linux/kprobes.h
int arch_check_ftrace_location(struct kprobe *p);

Then, we don't need to add any macros or kconfigs.

Thank you,

>
> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
> ---
> arch/Kconfig | 8 ++++++++
> kernel/kprobes.c | 36 +++++++++++++++++++++---------------
> 2 files changed, 29 insertions(+), 15 deletions(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 05d7a8a458d5..e1a8e0edf03f 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -85,6 +85,14 @@ config KPROBES_ON_FTRACE
> passing of pt_regs to function tracing, then kprobes can
> optimize on top of function tracing.
>
> +config ARCH_HANDLES_KPROBES_ON_FTRACE
> + def_bool n
> + help
> + If an architecture can handle kprobes on function tracer call
> + sites on own, then this option should be selected. This option
> + removes the check which otherwise prevents to set kprobes on
> + function tracer call sites.
> +
> config UPROBES
> def_bool n
> select PERCPU_RWSEM
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 3995f546d0f3..4b57fe9fbeb7 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1410,28 +1410,34 @@ static inline int check_kprobe_rereg(struct kprobe *p)
> return ret;
> }
>
> -static int check_kprobe_address_safe(struct kprobe *p,
> - struct module **probed_mod)
> +static int check_ftrace_location(struct kprobe *p)
> {
> - int ret = 0;
> unsigned long ftrace_addr;
>
> - /*
> - * If the address is located on a ftrace nop, set the
> - * breakpoint to the following instruction.
> - */
> ftrace_addr = ftrace_location((unsigned long)p->addr);
> - if (ftrace_addr) {
> -#ifdef CONFIG_KPROBES_ON_FTRACE
> - /* Given address is not on the instruction boundary */
> - if ((unsigned long)p->addr != ftrace_addr)
> - return -EILSEQ;
> + if (!ftrace_addr)
> + return 0;
> + /* Given address is not on the instruction boundary */
> + if ((unsigned long)p->addr != ftrace_addr)
> + return -EILSEQ;
> + /* If an architecture handles kprobes on ftrace, we're done */
> + if (IS_ENABLED(CONFIG_ARCH_HANDLES_KPROBES_ON_FTRACE))
> + return 0;
> + if (IS_ENABLED(CONFIG_KPROBES_ON_FTRACE)) {
> p->flags |= KPROBE_FLAG_FTRACE;
> -#else /* !CONFIG_KPROBES_ON_FTRACE */
> - return -EINVAL;
> -#endif
> + return 0;
> }
> + return -EINVAL;
> +}
> +
> +static int check_kprobe_address_safe(struct kprobe *p,
> + struct module **probed_mod)
> +{
> + int ret;
>
> + ret = check_ftrace_location(p);
> + if (ret)
> + return ret;
> jump_label_lock();
> preempt_disable();
>
>

--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com