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

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Message-Id: <1623685371.y5qy4nxer2.naveen@linux.ibm.com>
Date:   Mon, 14 Jun 2021 21:16:26 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>, ast@...nel.org,
        bpf@...r.kernel.org, Daniel Xu <dxu@...uu.xyz>,
        Josh Poimboeuf <jpoimboe@...hat.com>, kernel-team@...com,
        kuba@...nel.org, linux-ia64@...r.kernel.org,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        Abhishek Sagar <sagar.abhishek@...il.com>, tglx@...utronix.de,
        X86 ML <x86@...nel.org>, yhs@...com
Subject: Re: [PATCH -tip v7 03/13] kprobes: treewide: Remove
 trampoline_address from kretprobe_trampoline_handler()

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@...nel.org>
> Tested-by: Andrii Nakryik <andrii@...nel.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