Re: [PATCH -tip V3] [BUGFIX] kprobes/x86: Do not jump-optimize kprobes on irq entry code

[Masami Hiramatsu <mhiramat@kernel.org>]

On Tue, 25 Jul 2017 23:54:49 +0900
Masami Hiramatsu <mhiramat@kernel.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@kernel.org>
> Reported-by: Francis Deslauriers <francis.deslauriers@efficios.com>
> Tested-by: Francis Deslauriers <francis.deslauriers@efficios.com>
> ---
>  Changes in V3:
>   - Define __irqentry_text_start/end symbols when CONFIG_OPTPROBES=y.
> ---
>  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..a1b78f4 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_KPROBES)

Oops, this should be CONFIG_OPTPROBES...

>  /*
>   * We want to know which function is an entrypoint of a hardirq or a softirq.
>   */
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>