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SubjectRe: [PATCH v2 2/3] kprobes: adjust kprobe addr for KPROBES_ON_FTRACE
Hi Jisheng,

On Tue, 20 Aug 2019 03:53:31 +0000
Jisheng Zhang <Jisheng.Zhang@synaptics.com> wrote:

> For KPROBES_ON_FTRACE case, we need to adjust the kprobe's addr
> correspondingly.

Either KPROBES_ON_FTRACE=y or not, ftrace_location() check must be
done correctly. If it failed, kprobes can modify the instruction
which can be modified by ftrace.

>
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
> ---
> kernel/kprobes.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 9873fc627d61..3fd2f68644da 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1484,15 +1484,19 @@ static inline int check_kprobe_rereg(struct kprobe *p)
>
> int __weak arch_check_ftrace_location(struct kprobe *p)
> {
> - unsigned long ftrace_addr;
> + unsigned long ftrace_addr, addr = (unsigned long)p->addr;
>
> - ftrace_addr = ftrace_location((unsigned long)p->addr);
> +#ifdef CONFIG_KPROBES_ON_FTRACE
> + addr = ftrace_call_adjust(addr);
> +#endif
> + ftrace_addr = ftrace_location(addr);

No, this is not right way to do. If we always need to adjust address
before calling ftrace_location(), something wrong with ftrace_location()
interface.
ftrace_location(addr) must check the address is within the range which
can be changed by ftrace. (dyn->ip <= addr <= dyn->ip+MCOUNT_INSN_SIZE)


> if (ftrace_addr) {
> #ifdef CONFIG_KPROBES_ON_FTRACE
> /* Given address is not on the instruction boundary */
> - if ((unsigned long)p->addr != ftrace_addr)
> + if (addr != ftrace_addr)
> return -EILSEQ;
> p->flags |= KPROBE_FLAG_FTRACE;
> + p->addr = (kprobe_opcode_t *)addr;

And again, please don't change the p->addr silently.

Thank you,

> #else /* !CONFIG_KPROBES_ON_FTRACE */
> return -EINVAL;
> #endif
> --
> 2.23.0.rc1
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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