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

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Date:   Mon, 24 Jul 2017 14:28:36 +0000 (UTC)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Francis Deslauriers <francis.deslauriers@...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 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip] [BUGFIX] kprobes/x86: Do not jump-optimize kprobes
 on irq entry code

----- On Jul 24, 2017, at 9:50 AM, 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>
> ---
> arch/x86/entry/entry_64.S      |    2 +-
> arch/x86/include/asm/unwind.h  |    1 +
> arch/x86/kernel/kprobes/opt.c  |    4 ++--
> arch/x86/kernel/unwind_frame.c |    4 ++--
> 4 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index aa58155..9652c34 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -766,7 +766,7 @@ apicinterrupt3 \num trace(\sym) smp_trace(\sym)
> #endif
> 
> /* Make sure APIC interrupt handlers end up in the irqentry section: */
> -#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
> +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) ||
> defined(CONFIG_KPROBES)
> # define PUSH_SECTION_IRQENTRY	.pushsection .irqentry.text, "ax"
> # define POP_SECTION_IRQENTRY	.popsection
> #else
> diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h
> index e667649..a9896fb9 100644
> --- a/arch/x86/include/asm/unwind.h
> +++ b/arch/x86/include/asm/unwind.h
> @@ -28,6 +28,7 @@ void __unwind_start(struct unwind_state *state, struct
> task_struct *task,
> bool unwind_next_frame(struct unwind_state *state);
> 
> unsigned long unwind_get_return_address(struct unwind_state *state);
> +bool in_entry_code(unsigned long ip);
> 
> static inline bool unwind_done(struct unwind_state *state)
> {
> diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
> index 69ea0bc..a51c144 100644
> --- a/arch/x86/kernel/kprobes/opt.c
> +++ b/arch/x86/kernel/kprobes/opt.c
> @@ -39,6 +39,7 @@
> #include <asm/insn.h>
> #include <asm/debugreg.h>
> #include <asm/set_memory.h>
> +#include <asm/unwind.h>
> 
> #include "common.h"
> 
> @@ -253,8 +254,7 @@ static int can_optimize(unsigned long paddr)
> 	 * 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))
> +	if (in_entry_code(paddr))
> 		return 0;
> 
> 	/* Check there is enough space for a relative jump. */
> diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
> index b9389d7..95123ce 100644
> --- a/arch/x86/kernel/unwind_frame.c
> +++ b/arch/x86/kernel/unwind_frame.c
> @@ -84,14 +84,14 @@ static size_t regs_size(struct pt_regs *regs)
> 	return sizeof(*regs);
> }
> 
> -static bool in_entry_code(unsigned long ip)
> +bool in_entry_code(unsigned long ip)
> {
> 	char *addr = (char *)ip;
> 
> 	if (addr >= __entry_text_start && addr < __entry_text_end)
> 		return true;
> 
> -#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
> +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) ||
> defined(CONFIG_KPROBES)

Hi Masami,

With this patch applied on top of v4.12.3, I can generate a configuration
with CONFIG_KPROBES=y and CONFIG_FRAME_POINTER=n, which leads to:

arch/x86/built-in.o: In function `can_optimize':
/home/efficios/git/linux/arch/x86/kernel/kprobes/opt.c:250: undefined reference to `in_entry_code'

(see attached .config)

arch/x86/kernel/unwind_frame.c is only compiled when CONFIG_FRAME_POINTER
is enabled, but CONFIG_KPROBES does not depend on it.

Is unwind_frame.c really where in_entry_code() should be implemented, now
that its symbol becomes exposed to other compile units ?

Thanks,

Mathieu


> 	if (addr >= __irqentry_text_start && addr < __irqentry_text_end)
> 		return true;
>  #endif

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

View attachment "config" of type "text/x-mpsub" (190385 bytes)