[PATCH -tip v6 01/27] Documentation/kprobes: Fix to remove remaining jprobe

[PATCH -tip v6 01/27] Documentation/kprobes: Fix to remove remaining jprobe

[Masami Hiramatsu]

Remove jps from the document, since jprobe is removed.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
---
 Documentation/kprobes.txt |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
index 22208bf2386d..5ae80baf3921 100644
--- a/Documentation/kprobes.txt
+++ b/Documentation/kprobes.txt
@@ -474,7 +474,7 @@ error occurs during registration, all probes in the array, up to
 the bad probe, are safely unregistered before the register_*probes
 function returns.
 
-- kps/rps/jps: an array of pointers to ``*probe`` data structures
+- kps/rps: an array of pointers to ``*probe`` data structures
 - num: the number of the array entries.
 
 .. note::

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[PATCH -tip v6 25/27] kprobes/x86: Do not disable preempt on int3 path

[Masami Hiramatsu]

Since int3 and debug exception(for singlestep) are run with
IRQ disabled and while running single stepping we drop IF
from regs->flags, that path must not be preemptible. So we
can remove the preempt disable/enable calls from that path.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Suggested-by: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
---
 Changes in v3:
  - Split user-side changes to another patch
 Changes in v2:
  - Include user-side changes.
---
 Documentation/kprobes.txt      |   11 +++++------
 arch/x86/kernel/kprobes/core.c |   18 ++++--------------
 arch/x86/kernel/kprobes/opt.c  |    1 -
 3 files changed, 9 insertions(+), 21 deletions(-)

diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
index 907a3017c0f2..3e9e99ea751b 100644
--- a/Documentation/kprobes.txt
+++ b/Documentation/kprobes.txt
@@ -566,12 +566,11 @@ the same handler) may run concurrently on different CPUs.
 Kprobes does not use mutexes or allocate memory except during
 registration and unregistration.
 
-Probe handlers are run with preemption disabled.  Depending on the
-architecture and optimization state, handlers may also run with
-interrupts disabled (e.g., kretprobe handlers and optimized kprobe
-handlers run without interrupt disabled on x86/x86-64).  In any case,
-your handler should not yield the CPU (e.g., by attempting to acquire
-a semaphore).
+Probe handlers are run with preemption disabled or interrupt disabled,
+which depends on the architecture and optimization state.  (e.g.,
+kretprobe handlers and optimized kprobe handlers run without interrupt
+disabled on x86/x86-64).  In any case, your handler should not yield
+the CPU (e.g., by attempting to acquire a semaphore, or waiting I/O).
 
 Since a return probe is implemented by replacing the return
 address with the trampoline's address, stack backtraces and calls
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 814e26b7c8a2..f7104b256de7 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -594,7 +594,6 @@ static void setup_singlestep(struct kprobe *p, struct pt_regs *regs,
 		 * stepping.
 		 */
 		regs->ip = (unsigned long)p->ainsn.insn;
-		preempt_enable_no_resched();
 		return;
 	}
 #endif
@@ -667,12 +666,10 @@ int kprobe_int3_handler(struct pt_regs *regs)
 
 	addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t));
 	/*
-	 * We don't want to be preempted for the entire
-	 * duration of kprobe processing. We conditionally
-	 * re-enable preemption at the end of this function,
-	 * and also in reenter_kprobe() and setup_singlestep().
+	 * We don't want to be preempted for the entire duration of kprobe
+	 * processing. Since int3 and debug trap disables irqs and we clear
+	 * IF while singlestepping, it must be no preemptible.
 	 */
-	preempt_disable();
 
 	kcb = get_kprobe_ctlblk();
 	p = get_kprobe(addr);
@@ -694,10 +691,8 @@ int kprobe_int3_handler(struct pt_regs *regs)
 			 */
 			if (!p->pre_handler || !p->pre_handler(p, regs))
 				setup_singlestep(p, regs, kcb, 0);
-			else {
+			else
 				reset_current_kprobe();
-				preempt_enable_no_resched();
-			}
 			return 1;
 		}
 	} else if (*addr != BREAKPOINT_INSTRUCTION) {
@@ -711,11 +706,9 @@ int kprobe_int3_handler(struct pt_regs *regs)
 		 * the original instruction.
 		 */
 		regs->ip = (unsigned long)addr;
-		preempt_enable_no_resched();
 		return 1;
 	} /* else: not a kprobe fault; let the kernel handle it */
 
-	preempt_enable_no_resched();
 	return 0;
 }
 NOKPROBE_SYMBOL(kprobe_int3_handler);
@@ -966,8 +959,6 @@ int kprobe_debug_handler(struct pt_regs *regs)
 	}
 	reset_current_kprobe();
 out:
-	preempt_enable_no_resched();
-
 	/*
 	 * if somebody else is singlestepping across a probe point, flags
 	 * will have TF set, in which case, continue the remaining processing
@@ -1014,7 +1005,6 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 			restore_previous_kprobe(kcb);
 		else
 			reset_current_kprobe();
-		preempt_enable_no_resched();
 	} else if (kcb->kprobe_status == KPROBE_HIT_ACTIVE ||
 		   kcb->kprobe_status == KPROBE_HIT_SSDONE) {
 		/*
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 203d398802a3..eaf02f2e7300 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -491,7 +491,6 @@ int setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter)
 		regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX;
 		if (!reenter)
 			reset_current_kprobe();
-		preempt_enable_no_resched();
 		return 1;
 	}
 	return 0;

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[PATCH -tip v6 26/27] Documentation: kprobes: Add how to change the execution path

[Masami Hiramatsu]

Add a section that explaining how to change the execution
path with kprobes and warnings for some arch.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
---
 Documentation/kprobes.txt |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
index 3e9e99ea751b..8a98eed1521b 100644
--- a/Documentation/kprobes.txt
+++ b/Documentation/kprobes.txt
@@ -80,6 +80,26 @@ After the instruction is single-stepped, Kprobes executes the
 "post_handler," if any, that is associated with the kprobe.
 Execution then continues with the instruction following the probepoint.
 
+Changing Execution Path
+-----------------------
+
+Since the kprobes can probe into a running kernel code, it can change
+the register set, including instruction pointer. This operation
+requires maximum attention, such as keeping the stack frame, recovering
+execution path etc. Since it is operated on running kernel and need deep
+knowladge of the archtecture and concurrent computing, you can easily
+shot your foot.
+
+If you change the instruction pointer (and set up other related
+registers) in pre_handler, you must return !0 so that the kprobes
+stops single stepping and just returns to given address.
+This also means post_handler should not be called anymore.
+
+Note that this operation may be harder on some architectures which
+use TOC (Table of Contents) for function call, since you have to
+setup new TOC for your function in your module, and recover old
+one after back from it.
+
 Return Probes
 -------------
 

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Re: [PATCH -tip v6 26/27] Documentation: kprobes: Add how to change the execution path

[Randy Dunlap]

On 06/19/2018 09:16 AM, Masami Hiramatsu wrote:
> Add a section that explaining how to change the execution
> path with kprobes and warnings for some arch.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: linux-doc@vger.kernel.org
> ---
>  Documentation/kprobes.txt |   20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
> index 3e9e99ea751b..8a98eed1521b 100644
> --- a/Documentation/kprobes.txt
> +++ b/Documentation/kprobes.txt
> @@ -80,6 +80,26 @@ After the instruction is single-stepped, Kprobes executes the
>  "post_handler," if any, that is associated with the kprobe.
>  Execution then continues with the instruction following the probepoint.
>  

Hi,
I have a few small suggestions...


> +Changing Execution Path
> +-----------------------
> +
> +Since the kprobes can probe into a running kernel code, it can change

   Since kprobes can probe into running kernel code, it can change

> +the register set, including instruction pointer. This operation
> +requires maximum attention, such as keeping the stack frame, recovering
> +execution path etc. Since it is operated on running kernel and need deep

                       Since it operates on a running kernel and needs deep

> +knowladge of the archtecture and concurrent computing, you can easily

   knowledge of the architecture

> +shot your foot.

   shoot

> +
> +If you change the instruction pointer (and set up other related
> +registers) in pre_handler, you must return !0 so that the kprobes

                                                 so that kprobes

> +stops single stepping and just returns to given address.

                                          to the given address.

> +This also means post_handler should not be called anymore.
> +
> +Note that this operation may be harder on some architectures which
> +use TOC (Table of Contents) for function call, since you have to
> +setup new TOC for your function in your module, and recover old

   setup a new TOC for your function in your module, and recover the old

> +one after back from it.

   one after returning from it.

> +
>  Return Probes
>  -------------


-- 
~Randy
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Re: [PATCH -tip v6 26/27] Documentation: kprobes: Add how to change the execution path

[Masami Hiramatsu]

On Tue, 19 Jun 2018 09:31:49 -0700
Randy Dunlap <rdunlap@infradead.org> wrote:

> On 06/19/2018 09:16 AM, Masami Hiramatsu wrote:
> > Add a section that explaining how to change the execution
> > path with kprobes and warnings for some arch.
> > 
> > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> > Cc: Jonathan Corbet <corbet@lwn.net>
> > Cc: linux-doc@vger.kernel.org
> > ---
> >  Documentation/kprobes.txt |   20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> > 
> > diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
> > index 3e9e99ea751b..8a98eed1521b 100644
> > --- a/Documentation/kprobes.txt
> > +++ b/Documentation/kprobes.txt
> > @@ -80,6 +80,26 @@ After the instruction is single-stepped, Kprobes executes the
> >  "post_handler," if any, that is associated with the kprobe.
> >  Execution then continues with the instruction following the probepoint.
> >  
> 
> Hi,
> I have a few small suggestions...

Hi Randy,

Thank you for your suggestions!
All of those are good to me. I'll fix it:)

Thank you!

> 
> 
> > +Changing Execution Path
> > +-----------------------
> > +
> > +Since the kprobes can probe into a running kernel code, it can change
> 
>    Since kprobes can probe into running kernel code, it can change
> 
> > +the register set, including instruction pointer. This operation
> > +requires maximum attention, such as keeping the stack frame, recovering
> > +execution path etc. Since it is operated on running kernel and need deep
> 
>                        Since it operates on a running kernel and needs deep
> 
> > +knowladge of the archtecture and concurrent computing, you can easily
> 
>    knowledge of the architecture
> 
> > +shot your foot.
> 
>    shoot
> 
> > +
> > +If you change the instruction pointer (and set up other related
> > +registers) in pre_handler, you must return !0 so that the kprobes
> 
>                                                  so that kprobes
> 
> > +stops single stepping and just returns to given address.
> 
>                                           to the given address.
> 
> > +This also means post_handler should not be called anymore.
> > +
> > +Note that this operation may be harder on some architectures which
> > +use TOC (Table of Contents) for function call, since you have to
> > +setup new TOC for your function in your module, and recover old
> 
>    setup a new TOC for your function in your module, and recover the old
> 
> > +one after back from it.
> 
>    one after returning from it.
> 
> > +
> >  Return Probes
> >  -------------
> 
> 
> -- 
> ~Randy


-- 
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Re: [PATCH -tip v6 26/27] Documentation: kprobes: Add how to change the execution path

[Ingo Molnar]

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

> On Tue, 19 Jun 2018 09:31:49 -0700
> Randy Dunlap <rdunlap@infradead.org> wrote:
> 
> > On 06/19/2018 09:16 AM, Masami Hiramatsu wrote:
> > > Add a section that explaining how to change the execution
> > > path with kprobes and warnings for some arch.
> > > 
> > > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> > > Cc: Jonathan Corbet <corbet@lwn.net>
> > > Cc: linux-doc@vger.kernel.org
> > > ---
> > >  Documentation/kprobes.txt |   20 ++++++++++++++++++++
> > >  1 file changed, 20 insertions(+)
> > > 
> > > diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
> > > index 3e9e99ea751b..8a98eed1521b 100644
> > > --- a/Documentation/kprobes.txt
> > > +++ b/Documentation/kprobes.txt
> > > @@ -80,6 +80,26 @@ After the instruction is single-stepped, Kprobes executes the
> > >  "post_handler," if any, that is associated with the kprobe.
> > >  Execution then continues with the instruction following the probepoint.
> > >  
> > 
> > Hi,
> > I have a few small suggestions...
> 
> Hi Randy,
> 
> Thank you for your suggestions!
> All of those are good to me. I'll fix it:)

Could you please send a delta patch on top of your v6 series, with Randy credited, 
etc?

I've applied your series and will push it out once it passes all testing.

Thanks,

	Ingo
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Re: [PATCH -tip v6 26/27] Documentation: kprobes: Add how to change the execution path

[Masami Hiramatsu]

On Thu, 21 Jun 2018 12:35:46 +0200
Ingo Molnar <mingo@kernel.org> wrote:

> 
> * Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
> > On Tue, 19 Jun 2018 09:31:49 -0700
> > Randy Dunlap <rdunlap@infradead.org> wrote:
> > 
> > > On 06/19/2018 09:16 AM, Masami Hiramatsu wrote:
> > > > Add a section that explaining how to change the execution
> > > > path with kprobes and warnings for some arch.
> > > > 
> > > > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> > > > Cc: Jonathan Corbet <corbet@lwn.net>
> > > > Cc: linux-doc@vger.kernel.org
> > > > ---
> > > >  Documentation/kprobes.txt |   20 ++++++++++++++++++++
> > > >  1 file changed, 20 insertions(+)
> > > > 
> > > > diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
> > > > index 3e9e99ea751b..8a98eed1521b 100644
> > > > --- a/Documentation/kprobes.txt
> > > > +++ b/Documentation/kprobes.txt
> > > > @@ -80,6 +80,26 @@ After the instruction is single-stepped, Kprobes executes the
> > > >  "post_handler," if any, that is associated with the kprobe.
> > > >  Execution then continues with the instruction following the probepoint.
> > > >  
> > > 
> > > Hi,
> > > I have a few small suggestions...
> > 
> > Hi Randy,
> > 
> > Thank you for your suggestions!
> > All of those are good to me. I'll fix it:)
> 
> Could you please send a delta patch on top of your v6 series, with Randy credited, 
> etc?

Ok, Here's the delta patch.


> 
> I've applied your series and will push it out once it passes all testing.

Thanks!


From 103fc58ece99475b855e065bd48d780697b93bbc Mon Sep 17 00:00:00 2001
From: Masami Hiramatsu <mhiramat@kernel.org>
Date: Fri, 22 Jun 2018 15:05:49 +0900
Subject: [PATCH] Documentation/kprobes: Fix typo in Changing Execution Path
 section

Fix typo and clean it up according to the
comment from Randy.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Suggested-by: Randy Dunlap <rdunlap@infradead.org>
---
 Documentation/kprobes.txt | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
index 13d8efd..10f4499 100644
--- a/Documentation/kprobes.txt
+++ b/Documentation/kprobes.txt
@@ -83,22 +83,22 @@ Execution then continues with the instruction following the probepoint.
 Changing Execution Path
 -----------------------
 
-Since the kprobes can probe into a running kernel code, it can change
-the register set, including instruction pointer. This operation
-requires maximum attention, such as keeping the stack frame, recovering
-execution path etc. Since it is operated on running kernel and need deep
-knowladge of the archtecture and concurrent computing, you can easily
-shot your foot.
+Since kprobes can probe into a running kernel code, it can change the
+register set, including instruction pointer. This operation requires
+maximum care, such as keeping the stack frame, recovering the execution
+path etc. Since it operates on a running kernel and needs deep knowledge
+of computer architecture and concurrent computing, you can easily shoot
+your foot.
 
 If you change the instruction pointer (and set up other related
-registers) in pre_handler, you must return !0 so that the kprobes
-stops single stepping and just returns to given address.
+registers) in pre_handler, you must return !0 so that kprobes stops
+single stepping and just returns to the given address.
 This also means post_handler should not be called anymore.
 
-Note that this operation may be harder on some architectures which
-use TOC (Table of Contents) for function call, since you have to
-setup new TOC for your function in your module, and recover old
-one after back from it.
+Note that this operation may be harder on some architectures which use
+TOC (Table of Contents) for function call, since you have to setup a new
+TOC for your function in your module, and recover the old one after
+returning from it.
 
 Return Probes
 -------------
-- 
2.7.4
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