[PATCH 0/2] uprobes: Change handle_swbp() to expose bp_vaddr to handler_chain()

[PATCH 0/2] uprobes: Change handle_swbp() to expose bp_vaddr to handler_chain()

[Oleg Nesterov]

Hello.

Inspired by the recent uretrpobe RFC's. I think it simply makes no sense
to call handler/skip/arch_uprobe_pre_xol with regs->ip pointing to the
"random" address after the task hits bp.

Ananth, could you please confirm 2/2 can't break powerpc? It "obviously"
shouldn't because uprobe_get_swbp_addr() is a "nop" on ppc, but still
your ack is welcomed.

Oleg.

[PATCH 1/2] uprobes/x86: Change __skip_sstep() to actually skip the whole insn

[Oleg Nesterov]

__skip_sstep() doesn't update regs->ip. Currently this is correct
but only "by accident" and it doesn't skip the whole insn. Change
it to advance ->ip by the length of the detected 0x66*0x90 sequence.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 arch/x86/kernel/uprobes.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index c71025b..4e33a35 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -680,8 +680,11 @@ static bool __skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
 		if (auprobe->insn[i] == 0x66)
 			continue;
 
-		if (auprobe->insn[i] == 0x90)
+		if (auprobe->insn[i] == 0x90) {
+			regs->ip = uprobe_get_swbp_addr(regs);
+			regs->ip += i + 1;
 			return true;
+		}
 
 		break;
 	}
-- 
1.5.5.1

[PATCH 2/2] uprobes: Change handle_swbp() to expose bp_vaddr to handler_chain()

[Oleg Nesterov]

Change handle_swbp() to set regs->ip = bp_vaddr in advance, this is
what consumer->handler() needs but uprobe_get_swbp_addr() is not
exported.

This also simplifies the code and makes it more consistent across
the supported architectures. handle_swbp() becomes the only caller
of uprobe_get_swbp_addr().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 arch/x86/kernel/uprobes.c   |    1 -
 kernel/events/uprobes.c     |   15 +++++++--------
 kernel/trace/trace_uprobe.c |    4 ++--
 3 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 4e33a35..0ba4cfb 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -681,7 +681,6 @@ static bool __skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
 			continue;
 
 		if (auprobe->insn[i] == 0x90) {
-			regs->ip = uprobe_get_swbp_addr(regs);
 			regs->ip += i + 1;
 			return true;
 		}
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 59b6e97..f883813 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1504,6 +1504,10 @@ static void handle_swbp(struct pt_regs *regs)
 		}
 		return;
 	}
+
+	/* change it in advance for ->handler() and restart */
+	instruction_pointer_set(regs, bp_vaddr);
+
 	/*
 	 * TODO: move copy_insn/etc into _register and remove this hack.
 	 * After we hit the bp, _unregister + _register can install the
@@ -1511,14 +1515,14 @@ static void handle_swbp(struct pt_regs *regs)
 	 */
 	smp_rmb(); /* pairs with wmb() in install_breakpoint() */
 	if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags)))
-		goto restart;
+		goto out;
 
 	utask = current->utask;
 	if (!utask) {
 		utask = add_utask();
 		/* Cannot allocate; re-execute the instruction. */
 		if (!utask)
-			goto restart;
+			goto out;
 	}
 
 	handler_chain(uprobe, regs);
@@ -1531,12 +1535,7 @@ static void handle_swbp(struct pt_regs *regs)
 		return;
 	}
 
-restart:
-	/*
-	 * cannot singlestep; cannot skip instruction;
-	 * re-execute the instruction.
-	 */
-	instruction_pointer_set(regs, bp_vaddr);
+	/* can_skip_sstep() succeeded, or restart if can't singlestep */
 out:
 	put_uprobe(uprobe);
 }
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 38eee92..52caead 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -488,7 +488,7 @@ static void uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
 		return;
 
 	entry = ring_buffer_event_data(event);
-	entry->ip = uprobe_get_swbp_addr(task_pt_regs(current));
+	entry->ip = instruction_pointer(task_pt_regs(current));
 	data = (u8 *)&entry[1];
 	for (i = 0; i < tu->nr_args; i++)
 		call_fetch(&tu->args[i].fetch, regs, data + tu->args[i].offset);
@@ -663,7 +663,7 @@ static void uprobe_perf_func(struct trace_uprobe *tu, struct pt_regs *regs)
 	if (!entry)
 		goto out;
 
-	entry->ip = uprobe_get_swbp_addr(task_pt_regs(current));
+	entry->ip = instruction_pointer(task_pt_regs(current));
 	data = (u8 *)&entry[1];
 	for (i = 0; i < tu->nr_args; i++)
 		call_fetch(&tu->args[i].fetch, regs, data + tu->args[i].offset);
-- 
1.5.5.1

Re: [PATCH 2/2] uprobes: Change handle_swbp() to expose bp_vaddr to handler_chain()

[Ananth N Mavinakayanahalli]

On Sun, Dec 30, 2012 at 04:47:22PM +0100, Oleg Nesterov wrote:
> Change handle_swbp() to set regs->ip = bp_vaddr in advance, this is
> what consumer->handler() needs but uprobe_get_swbp_addr() is not
> exported.
> 
> This also simplifies the code and makes it more consistent across
> the supported architectures. handle_swbp() becomes the only caller
> of uprobe_get_swbp_addr().

The arch agnostic bits look fine to me.

> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>

Re: [PATCH 1/2] uprobes/x86: Change __skip_sstep() to actually skip the whole insn

[Anton Arapov]

On Sun, Dec 30, 2012 at 04:47:19PM +0100, Oleg Nesterov wrote:
> __skip_sstep() doesn't update regs->ip. Currently this is correct
> but only "by accident" and it doesn't skip the whole insn. Change
> it to advance ->ip by the length of the detected 0x66*0x90 sequence.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
>  arch/x86/kernel/uprobes.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index c71025b..4e33a35 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -680,8 +680,11 @@ static bool __skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
>  		if (auprobe->insn[i] == 0x66)
>  			continue;
>  
> -		if (auprobe->insn[i] == 0x90)
> +		if (auprobe->insn[i] == 0x90) {
> +			regs->ip = uprobe_get_swbp_addr(regs);
> +			regs->ip += i + 1;
>  			return true;
> +		}

  This change/routine is not obvious without the patch description, I
would appreciate some comment in the code. :) I believe it could help
some random developer in future.
  / I leave it to your judgement though /

Anton.

Re: [PATCH 1/2] uprobes/x86: Change __skip_sstep() to actually skip the whole insn

[Srikar Dronamraju]

* Oleg Nesterov <oleg@redhat.com> [2012-12-30 16:47:19]:

> __skip_sstep() doesn't update regs->ip. Currently this is correct
> but only "by accident" and it doesn't skip the whole insn. Change
> it to advance ->ip by the length of the detected 0x66*0x90 sequence.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> ---
>  arch/x86/kernel/uprobes.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index c71025b..4e33a35 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -680,8 +680,11 @@ static bool __skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
>  		if (auprobe->insn[i] == 0x66)
>  			continue;
> 
> -		if (auprobe->insn[i] == 0x90)
> +		if (auprobe->insn[i] == 0x90) {
> +			regs->ip = uprobe_get_swbp_addr(regs);
> +			regs->ip += i + 1;
>  			return true;
> +		}
> 
>  		break;
>  	}
> -- 
> 1.5.5.1
> 

Re: [PATCH 1/2] uprobes/x86: Change __skip_sstep() to actually skip the whole insn

[Srikar Dronamraju]

* Oleg Nesterov <oleg@redhat.com> [2012-12-30 16:47:19]:

> __skip_sstep() doesn't update regs->ip. Currently this is correct
> but only "by accident" and it doesn't skip the whole insn. Change
> it to advance ->ip by the length of the detected 0x66*0x90 sequence.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> ---
>  arch/x86/kernel/uprobes.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index c71025b..4e33a35 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -680,8 +680,11 @@ static bool __skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
>  		if (auprobe->insn[i] == 0x66)
>  			continue;
> 
> -		if (auprobe->insn[i] == 0x90)
> +		if (auprobe->insn[i] == 0x90) {
> +			regs->ip = uprobe_get_swbp_addr(regs);
> +			regs->ip += i + 1;
>  			return true;
> +		}
> 
>  		break;
>  	}
> -- 
> 1.5.5.1
> 

Re: [PATCH 2/2] uprobes: Change handle_swbp() to expose bp_vaddr to handler_chain()

[Srikar Dronamraju]

* Oleg Nesterov <oleg@redhat.com> [2012-12-30 16:47:22]:

> Change handle_swbp() to set regs->ip = bp_vaddr in advance, this is
> what consumer->handler() needs but uprobe_get_swbp_addr() is not
> exported.
> 
> This also simplifies the code and makes it more consistent across
> the supported architectures. handle_swbp() becomes the only caller
> of uprobe_get_swbp_addr().
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> ---
>  arch/x86/kernel/uprobes.c   |    1 -
>  kernel/events/uprobes.c     |   15 +++++++--------
>  kernel/trace/trace_uprobe.c |    4 ++--
>  3 files changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index 4e33a35..0ba4cfb 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -681,7 +681,6 @@ static bool __skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
>  			continue;
> 
>  		if (auprobe->insn[i] == 0x90) {
> -			regs->ip = uprobe_get_swbp_addr(regs);
>  			regs->ip += i + 1;
>  			return true;
>  		}
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 59b6e97..f883813 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1504,6 +1504,10 @@ static void handle_swbp(struct pt_regs *regs)
>  		}
>  		return;
>  	}
> +
> +	/* change it in advance for ->handler() and restart */
> +	instruction_pointer_set(regs, bp_vaddr);
> +
>  	/*
>  	 * TODO: move copy_insn/etc into _register and remove this hack.
>  	 * After we hit the bp, _unregister + _register can install the
> @@ -1511,14 +1515,14 @@ static void handle_swbp(struct pt_regs *regs)
>  	 */
>  	smp_rmb(); /* pairs with wmb() in install_breakpoint() */
>  	if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags)))
> -		goto restart;
> +		goto out;
> 
>  	utask = current->utask;
>  	if (!utask) {
>  		utask = add_utask();
>  		/* Cannot allocate; re-execute the instruction. */
>  		if (!utask)
> -			goto restart;
> +			goto out;
>  	}
> 
>  	handler_chain(uprobe, regs);
> @@ -1531,12 +1535,7 @@ static void handle_swbp(struct pt_regs *regs)
>  		return;
>  	}
> 
> -restart:
> -	/*
> -	 * cannot singlestep; cannot skip instruction;
> -	 * re-execute the instruction.
> -	 */
> -	instruction_pointer_set(regs, bp_vaddr);
> +	/* can_skip_sstep() succeeded, or restart if can't singlestep */
>  out:
>  	put_uprobe(uprobe);
>  }
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 38eee92..52caead 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -488,7 +488,7 @@ static void uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
>  		return;
> 
>  	entry = ring_buffer_event_data(event);
> -	entry->ip = uprobe_get_swbp_addr(task_pt_regs(current));
> +	entry->ip = instruction_pointer(task_pt_regs(current));
>  	data = (u8 *)&entry[1];
>  	for (i = 0; i < tu->nr_args; i++)
>  		call_fetch(&tu->args[i].fetch, regs, data + tu->args[i].offset);
> @@ -663,7 +663,7 @@ static void uprobe_perf_func(struct trace_uprobe *tu, struct pt_regs *regs)
>  	if (!entry)
>  		goto out;
> 
> -	entry->ip = uprobe_get_swbp_addr(task_pt_regs(current));
> +	entry->ip = instruction_pointer(task_pt_regs(current));
>  	data = (u8 *)&entry[1];
>  	for (i = 0; i < tu->nr_args; i++)
>  		call_fetch(&tu->args[i].fetch, regs, data + tu->args[i].offset);
> -- 
> 1.5.5.1
>