linux-kernel - Re: [PATCH -tip v4] [BUGFIX] kprobes/x86: Do not jump-optimize kprobes on irq entry code

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Date:   Thu, 27 Jul 2017 10:24:46 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Francis Deslauriers <francis.deslauriers@...icios.com>,
        mathieu.desnoyers@...icios.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Ananth N Mavinakayanahalli <ananth@...ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -tip v4] [BUGFIX] kprobes/x86: Do not jump-optimize
 kprobes on irq entry code


* Masami Hiramatsu <mhiramat@...nel.org> wrote:

> Since the kernel segment registers are not prepared at the
> entry of irq-entry code, if a kprobe on such code is
> jump-optimized, accessing per-cpu variables may cause
> kernel panic.
> However, if the kprobe is not optimized, it kicks int3
> exception and set segment registers correctly.
> 
> This checks probe-address and if it is in irq-entry code,
> it prohibits optimizing such kprobes. This means we can
> continuously probing such interrupt handlers by kprobes
> but it is not optimized anymore.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> Reported-by: Francis Deslauriers <francis.deslauriers@...icios.com>
> Tested-by: Francis Deslauriers <francis.deslauriers@...icios.com>
> ---
>  Changes in v4:
>   - Fix to use CONFIG_OPTPROBES instead of CONFIG_KPROBES.
> ---
>  arch/x86/kernel/kprobes/opt.c     |    9 ++++++---
>  include/asm-generic/vmlinux.lds.h |    6 ++++--
>  include/linux/interrupt.h         |    3 ++-
>  3 files changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
> index 69ea0bc..c26e7f9 100644
> --- a/arch/x86/kernel/kprobes/opt.c
> +++ b/arch/x86/kernel/kprobes/opt.c
> @@ -29,6 +29,7 @@
>  #include <linux/kallsyms.h>
>  #include <linux/ftrace.h>
>  #include <linux/frame.h>
> +#include <linux/interrupt.h>
>  
>  #include <asm/text-patching.h>
>  #include <asm/cacheflush.h>
> @@ -251,10 +252,12 @@ static int can_optimize(unsigned long paddr)
>  
>  	/*
>  	 * Do not optimize in the entry code due to the unstable
> -	 * stack handling.
> +	 * stack handling and registers setup.
>  	 */
> -	if ((paddr >= (unsigned long)__entry_text_start) &&
> -	    (paddr <  (unsigned long)__entry_text_end))
> +	if (((paddr >= (unsigned long)__entry_text_start) &&
> +	     (paddr <  (unsigned long)__entry_text_end)) ||
> +	    ((paddr >= (unsigned long)__irqentry_text_start) &&
> +	     (paddr <  (unsigned long)__irqentry_text_end)))
>  		return 0;
>  
>  	/* Check there is enough space for a relative jump. */
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index da0be9a..3092a1f 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -483,7 +483,8 @@
>  		*(.entry.text)						\
>  		VMLINUX_SYMBOL(__entry_text_end) = .;
>  
> -#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
> +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) ||	\
> +	defined(CONFIG_OPTPROBES)
>  #define IRQENTRY_TEXT							\
>  		ALIGN_FUNCTION();					\
>  		VMLINUX_SYMBOL(__irqentry_text_start) = .;		\
> @@ -493,7 +494,8 @@
>  #define IRQENTRY_TEXT
>  #endif
>  
> -#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
> +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) ||	\
> +	defined(CONFIG_OPTPROBES)
>  #define SOFTIRQENTRY_TEXT						\
>  		ALIGN_FUNCTION();					\
>  		VMLINUX_SYMBOL(__softirqentry_text_start) = .;		\
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index a2fdddd..f95b046 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -726,7 +726,8 @@ extern int early_irq_init(void);
>  extern int arch_probe_nr_irqs(void);
>  extern int arch_early_irq_init(void);
>  
> -#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
> +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) || \
> +	defined(CONFIG_OPTPROBES)

Please split the generic changes to asm-generic/vmlinux.lds.h and interrupt.h into 
a separate patch, with its own changelog, because this is not a kprobes/x86 only 
patch anymore.

Thanks,

	Ingo