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

[Masami Hiramatsu <mhiramat@kernel.org>]

On Thu, 27 Jul 2017 10:24:46 +0200
Ingo Molnar <mingo@kernel.org> wrote:

> 
> * 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 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.

OK. BTW, I think it is a good time to make a new (hidden) Kconfig entry for
irqentry, like CONFIG_IRQENTRY and above 3 configs select it. What would
you think?

Thank you,

> 
> Thanks,
> 
> 	Ingo


-- 
Masami Hiramatsu <mhiramat@kernel.org>