Re: [PATCH -tip v7 03/13] kprobes: treewide: Remove trampoline_address from kretprobe_trampoline_han

Naveen N. Rao
2021-06-14T15:58:26Z

Hi Masami,

Masami Hiramatsu wrote:
> Remove trampoline_address from kretprobe_trampoline_handler().
> Instead of passing the address, kretprobe_trampoline_handler()
> can use new kretprobe_trampoline_addr().
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> Tested-by: Andrii Nakryik <andrii@kernel.org>
> ---
> Changes in v3:
> - Remove wrong kretprobe_trampoline declaration from
> arch/x86/include/asm/kprobes.h.
> Changes in v2:
> - Remove arch_deref_entry_point() from comment.
> ---
> arch/arc/kernel/kprobes.c | 2 +-
> arch/arm/probes/kprobes/core.c | 3 +--
> arch/arm64/kernel/probes/kprobes.c | 3 +--
> arch/csky/kernel/probes/kprobes.c | 2 +-
> arch/ia64/kernel/kprobes.c | 5 ++---
> arch/mips/kernel/kprobes.c | 3 +--
> arch/parisc/kernel/kprobes.c | 4 ++--
> arch/powerpc/kernel/kprobes.c | 2 +-
> arch/riscv/kernel/probes/kprobes.c | 2 +-
> arch/s390/kernel/kprobes.c | 2 +-
> arch/sh/kernel/kprobes.c | 2 +-
> arch/sparc/kernel/kprobes.c | 2 +-
> arch/x86/include/asm/kprobes.h | 1 -
> arch/x86/kernel/kprobes/core.c | 2 +-
> include/linux/kprobes.h | 18 +++++++++++++-----
> kernel/kprobes.c | 3 +--
> 16 files changed, 29 insertions(+), 27 deletions(-)
>

<snip>

> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index d65c041b5c22..65dadd4238a2 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -205,15 +205,23 @@ extern void arch_prepare_kretprobe(struct kretprobe_instance *ri,
> struct pt_regs *regs);
> extern int arch_trampoline_kprobe(struct kprobe *p);
>
> +void kretprobe_trampoline(void);
> +/*
> + * Since some architecture uses structured function pointer,
> + * use dereference_function_descriptor() to get real function address.
> + */
> +static nokprobe_inline void *kretprobe_trampoline_addr(void)
> +{
> + return dereference_function_descriptor(kretprobe_trampoline);

I'm afraid this won't work correctly. For kernel functions, please use
dereference_kernel_function_descriptor() which checks if the function
has a descriptor before dereferencing it.

Thanks,
Naveen