linux-kernel - Re: [RFC,PATCH] kprobes - optimized kprobes might crash before setting kernel stack

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Date:	Tue, 15 Feb 2011 13:30:58 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [RFC,PATCH] kprobes - optimized kprobes might crash before
 setting kernel stack

On Tue, Feb 15, 2011 at 06:41:58PM +0900, Masami Hiramatsu wrote:
> (2011/02/15 0:12), Jiri Olsa wrote:
> > hi,
> > 
> > you can crash the kernel using kprobe tracer via:
> > 
> > echo "p system_call_after_swapgs" > ./kprobe_events
> > echo 1 > ./events/kprobes/enable
> 
> Ah, thank you very much!
> 
> > The reason is that at the system_call_after_swapgs label,
> > the kernel stack is not set up. If optimized kprobes are
> > enabled, the user space stack is being used in this case
> > (see optimized kprobe template) and this might result in a crash.
> 
> Verified here, and also it didn't occur when turning optimization
> off by sysctl. So this is a bug of kprobe jump optimization, not
> kprobes itself.
> 
> > Looks like there are several places like this over the entry_$(BIT)
> > code. First I thought it'd be ok to localize those places, but
> > I haven't found any reasonable/maintainable way to disable only those
> > places.
> 
> Hmm, agreed.
> 
> > So I switched off the whole entry code from optimizing, but this
> > also switch many safe places (attached patch - tested on x86_64).
> 
> I'm OK for this solution. I think possible another solution is using
> interrupt stack in optprobe template too. Anyway in short term, this
> solution will be good.

ok, I'll test on 32 bits and resend to Ingo

> 
> > Also not sure this crash falls in to the area of that once such
> > probe is used, user should know consequences..
> 
> User can see that those probe is not optimized via sysfs.

I cannot find this, where can I see this info?

thanks,
jirka

> 
> Thanks again,
> 
> > 
> > any ideas?
> > 
> > wbr,
> > jirka
> > 
> > 
> > Signed-off-by: Jiri Olsa <jolsa@...hat.com>
> > ---
> >  arch/x86/ia32/ia32entry.S         |    2 ++
> >  arch/x86/kernel/entry_32.S        |    6 ++++--
> >  arch/x86/kernel/entry_64.S        |    6 ++++--
> >  arch/x86/kernel/kprobes.c         |    8 ++++++++
> >  arch/x86/kernel/vmlinux.lds.S     |    1 +
> >  include/asm-generic/sections.h    |    1 +
> >  include/asm-generic/vmlinux.lds.h |    6 ++++++
> >  7 files changed, 26 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
> > index 0ed7896..50f1630 100644
> > --- a/arch/x86/ia32/ia32entry.S
> > +++ b/arch/x86/ia32/ia32entry.S
> > @@ -25,6 +25,8 @@
> >  #define sysretl_audit ia32_ret_from_sys_call
> >  #endif
> >  
> > +	.section .entry.text, "ax"
> > +
> >  #define IA32_NR_syscalls ((ia32_syscall_end - ia32_sys_call_table)/8)
> >  
> >  	.macro IA32_ARG_FIXUP noebp=0
> > diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
> > index c8b4efa..051b4e2 100644
> > --- a/arch/x86/kernel/entry_32.S
> > +++ b/arch/x86/kernel/entry_32.S
> > @@ -65,6 +65,8 @@
> >  #define sysexit_audit	syscall_exit_work
> >  #endif
> >  
> > +	.section .entry.text, "ax"
> > +
> >  /*
> >   * We use macros for low-level operations which need to be overridden
> >   * for paravirtualization.  The following will never clobber any registers:
> > @@ -788,7 +790,7 @@ ENDPROC(ptregs_clone)
> >   */
> >  .section .init.rodata,"a"
> >  ENTRY(interrupt)
> > -.text
> > +.entry.text
> >  	.p2align 5
> >  	.p2align CONFIG_X86_L1_CACHE_SHIFT
> >  ENTRY(irq_entries_start)
> > @@ -807,7 +809,7 @@ vector=FIRST_EXTERNAL_VECTOR
> >        .endif
> >        .previous
> >  	.long 1b
> > -      .text
> > +      .entry.text
> >  vector=vector+1
> >      .endif
> >    .endr
> > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> > index aed1ffb..0a0ed79 100644
> > --- a/arch/x86/kernel/entry_64.S
> > +++ b/arch/x86/kernel/entry_64.S
> > @@ -61,6 +61,8 @@
> >  #define __AUDIT_ARCH_LE	   0x40000000
> >  
> >  	.code64
> > +	.section .entry.text, "ax"
> > +
> >  #ifdef CONFIG_FUNCTION_TRACER
> >  #ifdef CONFIG_DYNAMIC_FTRACE
> >  ENTRY(mcount)
> > @@ -744,7 +746,7 @@ END(stub_rt_sigreturn)
> >   */
> >  	.section .init.rodata,"a"
> >  ENTRY(interrupt)
> > -	.text
> > +	.section .entry.text
> >  	.p2align 5
> >  	.p2align CONFIG_X86_L1_CACHE_SHIFT
> >  ENTRY(irq_entries_start)
> > @@ -763,7 +765,7 @@ vector=FIRST_EXTERNAL_VECTOR
> >        .endif
> >        .previous
> >  	.quad 1b
> > -      .text
> > +      .section .entry.text
> >  vector=vector+1
> >      .endif
> >    .endr
> > diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
> > index d91c477..d03bc1e 100644
> > --- a/arch/x86/kernel/kprobes.c
> > +++ b/arch/x86/kernel/kprobes.c
> > @@ -1276,6 +1276,14 @@ static int __kprobes can_optimize(unsigned long paddr)
> >  	if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
> >  		return 0;
> >  
> > +	/*
> > +	 * Do not optimize in the entry code due to the unstable
> > +	 * stack handling.
> > +	 */
> > +	if ((paddr >= (unsigned long ) __entry_text_start) &&
> > +	    (paddr <  (unsigned long ) __entry_text_end))
> > +		return 0;
> > +
> >  	/* Check there is enough space for a relative jump. */
> >  	if (size - offset < RELATIVEJUMP_SIZE)
> >  		return 0;
> > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> > index e9f7a3c..0381e1f 100644
> > --- a/arch/x86/kernel/vmlinux.lds.S
> > +++ b/arch/x86/kernel/vmlinux.lds.S
> > @@ -105,6 +105,7 @@ SECTIONS
> >  		SCHED_TEXT
> >  		LOCK_TEXT
> >  		KPROBES_TEXT
> > +		ENTRY_TEXT
> >  		IRQENTRY_TEXT
> >  		*(.fixup)
> >  		*(.gnu.warning)
> > diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
> > index b3bfabc..c1a1216 100644
> > --- a/include/asm-generic/sections.h
> > +++ b/include/asm-generic/sections.h
> > @@ -11,6 +11,7 @@ extern char _sinittext[], _einittext[];
> >  extern char _end[];
> >  extern char __per_cpu_load[], __per_cpu_start[], __per_cpu_end[];
> >  extern char __kprobes_text_start[], __kprobes_text_end[];
> > +extern char __entry_text_start[], __entry_text_end[];
> >  extern char __initdata_begin[], __initdata_end[];
> >  extern char __start_rodata[], __end_rodata[];
> >  
> > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> > index fe77e33..906c3ce 100644
> > --- a/include/asm-generic/vmlinux.lds.h
> > +++ b/include/asm-generic/vmlinux.lds.h
> > @@ -424,6 +424,12 @@
> >  		*(.kprobes.text)					\
> >  		VMLINUX_SYMBOL(__kprobes_text_end) = .;
> >  
> > +#define ENTRY_TEXT							\
> > +		ALIGN_FUNCTION();					\
> > +		VMLINUX_SYMBOL(__entry_text_start) = .;			\
> > +		*(.entry.text)						\
> > +		VMLINUX_SYMBOL(__entry_text_end) = .;
> > +
> >  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> >  #define IRQENTRY_TEXT							\
> >  		ALIGN_FUNCTION();					\
> 
> 
> -- 
> Masami HIRAMATSU
> 2nd Dept. Linux Technology Center
> Hitachi, Ltd., Systems Development Laboratory
> E-mail: masami.hiramatsu.pt@...achi.com
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