[RFC 0/8] ARM64: Uprobe support added

[RFC 0/8] ARM64: Uprobe support added

[Pratyush Anand]

These patches have been prepared on top of ARM64 kprobe v3 patches [1]
under review.

Unit test for following has been done so far and they have been found
working
    1. Normal instruction, which can be probed like sub, ldr, add etc.
    2. Instructions which can be simulated like ret.
    3. uretprobe



[1]https://lkml.org/lkml/2014/11/18/33

Pratyush Anand (8):
  ARM64: Move BRK opcodes defines from kprobes.h to insn.h
  ARM64: Refactor kprobes-arm64
  Kernel/uprobe: Define arch_uprobe_exception_notify as __weak
  ARM64: Add instruction_pointer_set function
  ARM64: Re-factor flush_ptrace_access
  ARM64: Handle TRAP_HWBRKPT for user mode as well
  ARM64: Handle TRAP_BRKPT for user mode as well
  ARM64: Add uprobe support

 arch/arm/kernel/uprobes.c                          |   6 -
 arch/arm64/Kconfig                                 |   3 +
 arch/arm64/include/asm/insn.h                      |   8 +
 arch/arm64/include/asm/probes.h                    |  26 ++-
 arch/arm64/include/asm/ptrace.h                    |   7 +
 arch/arm64/include/asm/thread_info.h               |   5 +-
 arch/arm64/include/asm/uprobes.h                   |  43 ++++
 arch/arm64/kernel/Makefile                         |   5 +-
 arch/arm64/kernel/debug-monitors.c                 |  14 +-
 arch/arm64/kernel/kprobes.c                        |  11 +-
 arch/arm64/kernel/kprobes.h                        |   7 +-
 .../kernel/{kprobes-arm64.c => probes-arm64.c}     |  84 +++----
 .../kernel/{kprobes-arm64.h => probes-arm64.h}     |  17 +-
 arch/arm64/kernel/probes-condn-check.c             |   2 +-
 arch/arm64/kernel/probes-decode.h                  |   4 +-
 arch/arm64/kernel/signal.c                         |   4 +-
 arch/arm64/kernel/uprobes.c                        | 255 +++++++++++++++++++++
 arch/arm64/mm/flush.c                              |  30 ++-
 kernel/events/uprobes.c                            |  18 ++
 19 files changed, 445 insertions(+), 104 deletions(-)
 create mode 100644 arch/arm64/include/asm/uprobes.h
 rename arch/arm64/kernel/{kprobes-arm64.c => probes-arm64.c} (79%)
 rename arch/arm64/kernel/{kprobes-arm64.h => probes-arm64.h} (60%)
 create mode 100644 arch/arm64/kernel/uprobes.c

-- 
2.1.0

[RFC 0/8] ARM64: Uprobe support added

[Pratyush Anand]

+Dave

Sorry, I took all cc list from your kprobe patches and forgot to add you. :(

Please review.

On Wednesday 31 December 2014 08:51 PM, Pratyush Anand wrote:
> These patches have been prepared on top of ARM64 kprobe v3 patches [1]
> under review.
>
> Unit test for following has been done so far and they have been found
> working
>      1. Normal instruction, which can be probed like sub, ldr, add etc.
>      2. Instructions which can be simulated like ret.
>      3. uretprobe
>
>
>
> [1]https://lkml.org/lkml/2014/11/18/33
>
> Pratyush Anand (8):
>    ARM64: Move BRK opcodes defines from kprobes.h to insn.h
>    ARM64: Refactor kprobes-arm64
>    Kernel/uprobe: Define arch_uprobe_exception_notify as __weak
>    ARM64: Add instruction_pointer_set function
>    ARM64: Re-factor flush_ptrace_access
>    ARM64: Handle TRAP_HWBRKPT for user mode as well
>    ARM64: Handle TRAP_BRKPT for user mode as well
>    ARM64: Add uprobe support
>
>   arch/arm/kernel/uprobes.c                          |   6 -
>   arch/arm64/Kconfig                                 |   3 +
>   arch/arm64/include/asm/insn.h                      |   8 +
>   arch/arm64/include/asm/probes.h                    |  26 ++-
>   arch/arm64/include/asm/ptrace.h                    |   7 +
>   arch/arm64/include/asm/thread_info.h               |   5 +-
>   arch/arm64/include/asm/uprobes.h                   |  43 ++++
>   arch/arm64/kernel/Makefile                         |   5 +-
>   arch/arm64/kernel/debug-monitors.c                 |  14 +-
>   arch/arm64/kernel/kprobes.c                        |  11 +-
>   arch/arm64/kernel/kprobes.h                        |   7 +-
>   .../kernel/{kprobes-arm64.c => probes-arm64.c}     |  84 +++----
>   .../kernel/{kprobes-arm64.h => probes-arm64.h}     |  17 +-
>   arch/arm64/kernel/probes-condn-check.c             |   2 +-
>   arch/arm64/kernel/probes-decode.h                  |   4 +-
>   arch/arm64/kernel/signal.c                         |   4 +-
>   arch/arm64/kernel/uprobes.c                        | 255 +++++++++++++++++++++
>   arch/arm64/mm/flush.c                              |  30 ++-
>   kernel/events/uprobes.c                            |  18 ++
>   19 files changed, 445 insertions(+), 104 deletions(-)
>   create mode 100644 arch/arm64/include/asm/uprobes.h
>   rename arch/arm64/kernel/{kprobes-arm64.c => probes-arm64.c} (79%)
>   rename arch/arm64/kernel/{kprobes-arm64.h => probes-arm64.h} (60%)
>   create mode 100644 arch/arm64/kernel/uprobes.c
>

[RFC 8/8] ARM64: Add uprobe support

[Oleg Nesterov]

Hi Pratyush,

I'll try to actually read this patch (and the whole series) later, just
a couple of quick questions for now.

On 12/31, Pratyush Anand wrote:
>
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -205,6 +205,7 @@ static inline int valid_user_regs(struct user_pt_regs *regs)
>
>  #define instruction_pointer(regs)	((regs)->pc)
>  #define stack_pointer(regs)		((regs)->sp)
> +#define procedure_link_pointer(regs)	((regs)->regs[30])

perhaps it makes sense to change (at least) arch_prepare_kretprobe() to use
the new helper? OK, we can do this later.

> +/* Single step context for uprobe */
> +struct uprobe_step_ctx {
> +	struct list_head node;
> +	unsigned long match_addr;
> +};

I don't understand this... please see below.

> +struct arch_uprobe_task {
> +	unsigned long saved_fault_code;
> +	u64 saved_user_pc;
> +	struct uprobe_step_ctx ss_ctx;
> +};

saved_user_pc looks unneeded, you can rely on uprobe_task->vaddr ?

> +++ b/arch/arm64/kernel/uprobes.c
> @@ -0,0 +1,255 @@
> +/*
> + * Copyright (C) 2014 Pratyush Anand <panand@redhat.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +#include <linux/highmem.h>
> +#include <linux/ptrace.h>
> +#include <linux/uprobes.h>
> +#include <asm/debug-monitors.h>
> +#include <asm/probes.h>
> +
> +#include "probes-arm64.h"
> +
> +#define UPROBE_INV_FAULT_CODE	UINT_MAX
> +
> +static LIST_HEAD(step_ctx);
> +static DEFINE_RWLOCK(step_ctx_lock);
> +
> +static void add_ss_context(struct uprobe_task *utask)
> +{
> +	struct uprobe_step_ctx *ss_ctx = &utask->autask.ss_ctx;
> +
> +	ss_ctx->match_addr = utask->xol_vaddr;
> +	write_lock(&step_ctx_lock);
> +	list_add(&ss_ctx->node, &step_ctx);
> +	write_unlock(&step_ctx_lock);
> +}
> +
> +static struct uprobe_step_ctx *find_ss_context(unsigned long vaddr)
> +{
> +	struct uprobe_step_ctx *ss_ctx;
> +
> +	read_lock(&step_ctx_lock);
> +	list_for_each_entry(ss_ctx, &step_ctx, node)	{
> +		if (ss_ctx->match_addr == vaddr) {
> +			read_unlock(&step_ctx_lock);
> +			return ss_ctx;
> +		}
> +	}
> +	read_unlock(&step_ctx_lock);
> +
> +	return NULL;
> +}

This looks very wrong to me, but perhaps because I do not understand
why do we need these *_ss_context() helpers.

> +static void del_ss_context(struct uprobe_task *utask)
> +{
> +	struct uprobe_step_ctx *ss_ctx = find_ss_context(utask->xol_vaddr);
> +
> +	if (ss_ctx) {
> +		write_lock(&step_ctx_lock);
> +		list_del(&ss_ctx->node);
> +		write_unlock(&step_ctx_lock);
> +	} else {
> +		WARN_ON(1);
> +	}
> +}

Don't we need del_ss_context() in arch_uprobe_abort_xol() ? But this is
minor.

Why we can trust find_ss_context() ? What if another thread also called
add_ss_context() with the same (virtual) ->xol_vaddr ?

But the main question is: why do we need add/find_ss_context ?? Please
explain.

> +int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
> +{
> +	struct uprobe_task *utask = current->utask;
> +
> +	/* saved fault code is restored in post_xol */
> +	utask->autask.saved_fault_code = current->thread.fault_code;
> +
> +	/* An invalid fault code between pre/post xol event */
> +	current->thread.fault_code = UPROBE_INV_FAULT_CODE;
> +
> +	/* Save user pc */
> +	utask->autask.saved_user_pc = task_pt_regs(current)->user_regs.pc;
> +
> +	/* Instruction point to execute ol */
> +	instruction_pointer_set(regs, utask->xol_vaddr);
> +
> +	add_ss_context(utask);
> +
> +	user_enable_single_step(current);
> +
> +	return 0;
> +}
> +
> +int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
> +{
> +	struct uprobe_task *utask = current->utask;
> +
> +	WARN_ON_ONCE(current->thread.fault_code != UPROBE_INV_FAULT_CODE);
> +
> +	/* restore fault code */
> +	current->thread.fault_code = utask->autask.saved_fault_code;
> +
> +	/* restore user pc */
> +	task_pt_regs(current)->user_regs.pc = utask->autask.saved_user_pc;
> +
> +	/* Instruction point to execute next to breakpoint address */
> +	instruction_pointer_set(regs, utask->vaddr + 4);
> +
> +	del_ss_context(utask);
> +
> +	user_disable_single_step(current);
> +
> +	return 0;
> +}

task_pt_regs() above looks strange. We we can't use "struct pt_regs *regs"
passed as an argument?

See also the note about .saved_user_pc above. I think you can use
utask->vaddr instead.

And why do you need to play with ->user_regs.pc?? instruction_pointer_set()
after that modifies the same word?

Or it is possible that regs != task_pt_regs(current) ? (to remind, I do not
know arm ;)

Could you also explain

	instruction_pointer_set(regs, utask->vaddr + 4);

?

I mean, I do not understand why this is always correct. What if the probed
insn is "jmp" (I do not know arm64's name for jump) ?

Probably this is correct because in this case arm_probe_decode_insn() should
return INSN_GOOD_NO_SLOT and this insn will be emulated? If yes, this needs a
comment, imo.

> +static int uprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
> +{
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
> +	uprobe_pre_sstep_notifier(regs);
> +	local_irq_restore(flags);
> +
> +	return 0;
> +}

Again, you do not need to disable irqs around uprobe_pre_sstep_notifier().

And I am not sure I understand the logic... "return 0" actually means
"return DBG_HOOK_HANDLED", right?

I do not understand this register_break_hook() interface and the usage
of .esr_mask/esr_val. But given that this patch adds BRK64_ESR_UPROBES
and uses BRK64_OPCODE_UPROBES, I will assume that uprobe_breakpoint_handler()
will be called if this exception was triggered by UPROBE_SWBP_INSN.

In this case, why the unconditional DBG_HOOK_HANDLED is correct? For example,
what if the application itself or debugger use UPROBE_SWBP_INSN for (self)
debugging and this task has no uprobes? In this case uprobe_pre_sstep_notifier()
will do nothing, it won't set TIF_UPROBES and handle_swbp() won't be called.

IOW, shouldn't it do

	if (user_mode(regs) && uprobe_pre_sstep_notifier(regs))
		return DBG_HOOK_HANDLED;
	return DBG_HOOK_ERROR;

?

> +static int uprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
> +{
> +	unsigned long flags;
> +
> +	if (!find_ss_context(regs->pc - 4))
> +		return DBG_HOOK_ERROR;
> +
> +	local_irq_save(flags);
> +	uprobe_post_sstep_notifier(regs);
> +	local_irq_restore(flags);
> +
> +	return 0;
> +}

The same. No need to clear irqs, and please explain why we can't rely
on user_mode() && uprobe_post_sstep_notifier(), and why do we
need find_ss_context().

> +void flush_uprobe_xol_access(struct page *page, unsigned long uaddr,
> +		void *kaddr, unsigned long len)
> +{
> +	__flush_ptrace_access(page, uaddr, kaddr, len);
> +}

I have some concerns... I'll reply to 5/8 which adds __flush_ptrace_access.

Oleg.

[RFC 3/8] Kernel/uprobe: Define arch_uprobe_exception_notify as __weak

[Oleg Nesterov]

On 12/31, Pratyush Anand wrote:
>
> Both ARM and ARM64 handle uprobe exceptions through their own hooks.So
> nothing to be done in arch_uprobe_exception_notify except to return
> NOTIFY_DONE. Implement this as weak default function and remove
> definition from arm arch code.
>
> Signed-off-by: Pratyush Anand <panand@redhat.com>
> ---
>  arch/arm/kernel/uprobes.c |  6 ------
>  kernel/events/uprobes.c   | 18 ++++++++++++++++++
>  2 files changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm/kernel/uprobes.c b/arch/arm/kernel/uprobes.c
> index 56adf9c1fde0..0f3663ca82fc 100644
> --- a/arch/arm/kernel/uprobes.c
> +++ b/arch/arm/kernel/uprobes.c
> @@ -178,12 +178,6 @@ void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
>  	instruction_pointer_set(regs, utask->vaddr);
>  }
>
> -int arch_uprobe_exception_notify(struct notifier_block *self,
> -				 unsigned long val, void *data)
> -{
> -	return NOTIFY_DONE;
> -}

I agree, this is ugly. But I disagree with this change.

I think we should simply kill uprobe_exception_nb and unexport
arch_uprobe_exception_notify on x86/powerpc, and in fact I was going to do
this a long ago.

I'll send the patch later. Until then please add the dummy arch_uprobe_exception_notify()
like arch/arm does, to make the generic code happy.

Oleg.

[RFC 5/8] ARM64: Re-factor flush_ptrace_access

[Oleg Nesterov]

On 12/31, Pratyush Anand wrote:
>
> Re-factor flush_ptrace_access to reuse vma independent part.

But for what? The changelog should explain this.

> Signed-off-by: Pratyush Anand <panand@redhat.com>
> ---
>  arch/arm64/mm/flush.c | 24 +++++++++++++++---------
>  1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> index b6f14e8d2121..9a4dd6f39cfb 100644
> --- a/arch/arm64/mm/flush.c
> +++ b/arch/arm64/mm/flush.c
> @@ -34,19 +34,25 @@ void flush_cache_range(struct vm_area_struct *vma, unsigned long start,
>  		__flush_icache_all();
>  }
>
> +static void __flush_ptrace_access(struct page *page, unsigned long uaddr,
> +		void *kaddr, unsigned long len)
> +{
> +	unsigned long addr = (unsigned long)kaddr;
> +
> +	if (icache_is_aliasing()) {
> +		__flush_dcache_area(kaddr, len);
> +		__flush_icache_all();
> +	} else {
> +		flush_icache_range(addr, addr + len);
> +	}
> +}
> +
>  static void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
>  				unsigned long uaddr, void *kaddr,
>  				unsigned long len)
>  {
> -	if (vma->vm_flags & VM_EXEC) {
> -		unsigned long addr = (unsigned long)kaddr;
> -		if (icache_is_aliasing()) {
> -			__flush_dcache_area(kaddr, len);
> -			__flush_icache_all();
> -		} else {
> -			flush_icache_range(addr, addr + len);
> -		}
> -	}
> +	if (vma->vm_flags & VM_EXEC)
> +		__flush_ptrace_access(page, uaddr, kaddr, len);
>  }

So why uprobes can't use flush_ptrace_access() ? flush_uprobe_xol_access() is
called by arch_uprobe_copy_ixol(), and xol vma has VM_EXEC bit set.

Oleg.

[RFC 6/8] ARM64: Handle TRAP_HWBRKPT for user mode as well

[Oleg Nesterov]

Let me repeat once again that I know absolutely nothing about arm* ;)

On 12/31, Pratyush Anand wrote:
>
> uprobe registers a handler at step_hook. So, single_step_handler now
> checks for user mode as well if there is a valid hook.
>
> Signed-off-by: Pratyush Anand <panand@redhat.com>
> ---
>  arch/arm64/kernel/debug-monitors.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
> index b056369fd47d..2676b8655241 100644
> --- a/arch/arm64/kernel/debug-monitors.c
> +++ b/arch/arm64/kernel/debug-monitors.c
> @@ -236,6 +236,9 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
>  	if (!reinstall_suspended_bps(regs))
>  		return 0;
>
> +	if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
> +		return 0;
> +
>  	if (user_mode(regs)) {
>  		info.si_signo = SIGTRAP;
>  		info.si_errno = 0;
> @@ -251,9 +254,6 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
>  		 */
>  		user_rewind_single_step(current);
>  	} else {
> -		if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
> -			return 0;
> -

Agreed, we need something like this change...

But did you verify that it can't break other users of register_step_hook() ?
The current handlers do not check user_mode() == F, they assume that they
can't be called otherwise.

If this all is correct, please explain why in the changelog.

The same for the next patch.

Oleg.

[RFC 5/8] ARM64: Re-factor flush_ptrace_access

[Oleg Nesterov]

On 01/02, Oleg Nesterov wrote:
>
> On 12/31, Pratyush Anand wrote:
> >
> > Re-factor flush_ptrace_access to reuse vma independent part.
>
> But for what? The changelog should explain this.
>
> > Signed-off-by: Pratyush Anand <panand@redhat.com>
> > ---
> >  arch/arm64/mm/flush.c | 24 +++++++++++++++---------
> >  1 file changed, 15 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> > index b6f14e8d2121..9a4dd6f39cfb 100644
> > --- a/arch/arm64/mm/flush.c
> > +++ b/arch/arm64/mm/flush.c
> > @@ -34,19 +34,25 @@ void flush_cache_range(struct vm_area_struct *vma, unsigned long start,
> >  		__flush_icache_all();
> >  }
> >
> > +static void __flush_ptrace_access(struct page *page, unsigned long uaddr,
> > +		void *kaddr, unsigned long len)
> > +{
> > +	unsigned long addr = (unsigned long)kaddr;
> > +
> > +	if (icache_is_aliasing()) {
> > +		__flush_dcache_area(kaddr, len);
> > +		__flush_icache_all();
> > +	} else {
> > +		flush_icache_range(addr, addr + len);
> > +	}
> > +}
> > +
> >  static void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
> >  				unsigned long uaddr, void *kaddr,
> >  				unsigned long len)
> >  {
> > -	if (vma->vm_flags & VM_EXEC) {
> > -		unsigned long addr = (unsigned long)kaddr;
> > -		if (icache_is_aliasing()) {
> > -			__flush_dcache_area(kaddr, len);
> > -			__flush_icache_all();
> > -		} else {
> > -			flush_icache_range(addr, addr + len);
> > -		}
> > -	}
> > +	if (vma->vm_flags & VM_EXEC)
> > +		__flush_ptrace_access(page, uaddr, kaddr, len);
> >  }
>
> So why uprobes can't use flush_ptrace_access() ? flush_uprobe_xol_access() is
> called by arch_uprobe_copy_ixol(), and xol vma has VM_EXEC bit set.

Ah, sorry, I forgot that arch_uprobe_copy_ixol() doesn't have "vma" so it
can't use flush_ptrace_access()... perhaps you can update the changelog.

Oleg.

[RFC 8/8] ARM64: Add uprobe support

[Pratyush Anand]

On Friday 02 January 2015 10:53 PM, Oleg Nesterov wrote:
> Hi Pratyush,
>
> I'll try to actually read this patch (and the whole series) later, just
> a couple of quick questions for now.
>
> On 12/31, Pratyush Anand wrote:
>>
>> --- a/arch/arm64/include/asm/ptrace.h
>> +++ b/arch/arm64/include/asm/ptrace.h
>> @@ -205,6 +205,7 @@ static inline int valid_user_regs(struct user_pt_regs *regs)
>>
>>   #define instruction_pointer(regs)	((regs)->pc)
>>   #define stack_pointer(regs)		((regs)->sp)
>> +#define procedure_link_pointer(regs)	((regs)->regs[30])
>
> perhaps it makes sense to change (at least) arch_prepare_kretprobe() to use
> the new helper? OK, we can do this later.

Yes.

>
>> +/* Single step context for uprobe */
>> +struct uprobe_step_ctx {
>> +	struct list_head node;
>> +	unsigned long match_addr;
>> +};
>
> I don't understand this... please see below.
>
>> +struct arch_uprobe_task {
>> +	unsigned long saved_fault_code;
>> +	u64 saved_user_pc;
>> +	struct uprobe_step_ctx ss_ctx;
>> +};
>
> saved_user_pc looks unneeded, you can rely on uprobe_task->vaddr ?

Probably yes. Will change.

>
>> +++ b/arch/arm64/kernel/uprobes.c
>> @@ -0,0 +1,255 @@
>> +/*
>> + * Copyright (C) 2014 Pratyush Anand <panand@redhat.com>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + */
>> +#include <linux/highmem.h>
>> +#include <linux/ptrace.h>
>> +#include <linux/uprobes.h>
>> +#include <asm/debug-monitors.h>
>> +#include <asm/probes.h>
>> +
>> +#include "probes-arm64.h"
>> +
>> +#define UPROBE_INV_FAULT_CODE	UINT_MAX
>> +
>> +static LIST_HEAD(step_ctx);
>> +static DEFINE_RWLOCK(step_ctx_lock);
>> +
>> +static void add_ss_context(struct uprobe_task *utask)
>> +{
>> +	struct uprobe_step_ctx *ss_ctx = &utask->autask.ss_ctx;
>> +
>> +	ss_ctx->match_addr = utask->xol_vaddr;
>> +	write_lock(&step_ctx_lock);
>> +	list_add(&ss_ctx->node, &step_ctx);
>> +	write_unlock(&step_ctx_lock);
>> +}
>> +
>> +static struct uprobe_step_ctx *find_ss_context(unsigned long vaddr)
>> +{
>> +	struct uprobe_step_ctx *ss_ctx;
>> +
>> +	read_lock(&step_ctx_lock);
>> +	list_for_each_entry(ss_ctx, &step_ctx, node)	{
>> +		if (ss_ctx->match_addr == vaddr) {
>> +			read_unlock(&step_ctx_lock);
>> +			return ss_ctx;
>> +		}
>> +	}
>> +	read_unlock(&step_ctx_lock);
>> +
>> +	return NULL;
>> +}
>
> This looks very wrong to me, but perhaps because I do not understand
> why do we need these *_ss_context() helpers.
>
>> +static void del_ss_context(struct uprobe_task *utask)
>> +{
>> +	struct uprobe_step_ctx *ss_ctx = find_ss_context(utask->xol_vaddr);
>> +
>> +	if (ss_ctx) {
>> +		write_lock(&step_ctx_lock);
>> +		list_del(&ss_ctx->node);
>> +		write_unlock(&step_ctx_lock);
>> +	} else {
>> +		WARN_ON(1);
>> +	}
>> +}
>
> Don't we need del_ss_context() in arch_uprobe_abort_xol() ? But this is
> minor.

Thanks. Yes, we need del_ss_context() in arch_uprobe_abort_xol().

>
> Why we can trust find_ss_context() ? What if another thread also called
> add_ss_context() with the same (virtual) ->xol_vaddr ?

OK..So xol_vaddr is not unique, then need to look for something else 
which could be unique for each probe.

>
> But the main question is: why do we need add/find_ss_context ?? Please
> explain.
>

See arch/arm64/kernel/debug-monitors.c: call_step_hook

Unlike breakpoint exception, there is no ESR info check for step 
exception. So, it is the responsibility of step handler 
(uprobe_single_step_handler) to make sure that exception was generated 
for it.

>> +int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
>> +{
>> +	struct uprobe_task *utask = current->utask;
>> +
>> +	/* saved fault code is restored in post_xol */
>> +	utask->autask.saved_fault_code = current->thread.fault_code;
>> +
>> +	/* An invalid fault code between pre/post xol event */
>> +	current->thread.fault_code = UPROBE_INV_FAULT_CODE;
>> +
>> +	/* Save user pc */
>> +	utask->autask.saved_user_pc = task_pt_regs(current)->user_regs.pc;
>> +
>> +	/* Instruction point to execute ol */
>> +	instruction_pointer_set(regs, utask->xol_vaddr);
>> +
>> +	add_ss_context(utask);
>> +
>> +	user_enable_single_step(current);
>> +
>> +	return 0;
>> +}
>> +
>> +int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
>> +{
>> +	struct uprobe_task *utask = current->utask;
>> +
>> +	WARN_ON_ONCE(current->thread.fault_code != UPROBE_INV_FAULT_CODE);
>> +
>> +	/* restore fault code */
>> +	current->thread.fault_code = utask->autask.saved_fault_code;
>> +
>> +	/* restore user pc */
>> +	task_pt_regs(current)->user_regs.pc = utask->autask.saved_user_pc;
>> +
>> +	/* Instruction point to execute next to breakpoint address */
>> +	instruction_pointer_set(regs, utask->vaddr + 4);
>> +
>> +	del_ss_context(utask);
>> +
>> +	user_disable_single_step(current);
>> +
>> +	return 0;
>> +}
>
> task_pt_regs() above looks strange. We we can't use "struct pt_regs *regs"
> passed as an argument?
>
> See also the note about .saved_user_pc above. I think you can use
> utask->vaddr instead.
>
> And why do you need to play with ->user_regs.pc?? instruction_pointer_set()
> after that modifies the same word?
>
> Or it is possible that regs != task_pt_regs(current) ? (to remind, I do not
> know arm ;)
>
> Could you also explain
>
> 	instruction_pointer_set(regs, utask->vaddr + 4);
>
> ?
>

Correct, saved_user_pc is not needed and also no need to play with 
->user_regs.pc. instruction_pointer_set should be sufficient.


> I mean, I do not understand why this is always correct. What if the probed
> insn is "jmp" (I do not know arm64's name for jump) ?
>
> Probably this is correct because in this case arm_probe_decode_insn() should
> return INSN_GOOD_NO_SLOT and this insn will be emulated? If yes, this needs a
> comment, imo.
>

Yes, a branch instruction like b or bl or ret will be simulated.

>> +static int uprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
>> +{
>> +	unsigned long flags;
>> +
>> +	local_irq_save(flags);
>> +	uprobe_pre_sstep_notifier(regs);
>> +	local_irq_restore(flags);
>> +
>> +	return 0;
>> +}
>
> Again, you do not need to disable irqs around uprobe_pre_sstep_notifier().

OK. (Actually took it from arch/arm/kernel/uprobe.c)

>
> And I am not sure I understand the logic... "return 0" actually means
> "return DBG_HOOK_HANDLED", right?

Yes. So better I will put return DBG_HOOK_HANDLED;

>
> I do not understand this register_break_hook() interface and the usage
> of .esr_mask/esr_val. But given that this patch adds BRK64_ESR_UPROBES
> and uses BRK64_OPCODE_UPROBES, I will assume that uprobe_breakpoint_handler()
> will be called if this exception was triggered by UPROBE_SWBP_INSN.

Correct.

>
> In this case, why the unconditional DBG_HOOK_HANDLED is correct? For example,
> what if the application itself or debugger use UPROBE_SWBP_INSN for (self)
> debugging and this task has no uprobes? In this case uprobe_pre_sstep_notifier()
> will do nothing, it won't set TIF_UPROBES and handle_swbp() won't be called.
>
> IOW, shouldn't it do
>
> 	if (user_mode(regs) && uprobe_pre_sstep_notifier(regs))
> 		return DBG_HOOK_HANDLED;
> 	return DBG_HOOK_ERROR;
>
> ?

Thanks for pointing out this bug with the code.
Your point seems pretty valid.

>
>> +static int uprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
>> +{
>> +	unsigned long flags;
>> +
>> +	if (!find_ss_context(regs->pc - 4))
>> +		return DBG_HOOK_ERROR;
>> +
>> +	local_irq_save(flags);
>> +	uprobe_post_sstep_notifier(regs);
>> +	local_irq_restore(flags);
>> +
>> +	return 0;
>> +}
>
> The same. No need to clear irqs, and please explain why we can't rely
> on user_mode() && uprobe_post_sstep_notifier(), and why do we
> need find_ss_context().
>

I had not looked into uprobe_post_sstep_notifier implementtaion.I think, 
you are right.


Thanks for all these valuable comments.

~Pratyush


>> +void flush_uprobe_xol_access(struct page *page, unsigned long uaddr,
>> +		void *kaddr, unsigned long len)
>> +{
>> +	__flush_ptrace_access(page, uaddr, kaddr, len);
>> +}
>
> I have some concerns... I'll reply to 5/8 which adds __flush_ptrace_access.
>
> Oleg.
>

[RFC 3/8] Kernel/uprobe: Define arch_uprobe_exception_notify as __weak

[Pratyush Anand]

On Friday 02 January 2015 11:13 PM, Oleg Nesterov wrote:
> On 12/31, Pratyush Anand wrote:
>>
>> Both ARM and ARM64 handle uprobe exceptions through their own hooks.So
>> nothing to be done in arch_uprobe_exception_notify except to return
>> NOTIFY_DONE. Implement this as weak default function and remove
>> definition from arm arch code.
>>
>> Signed-off-by: Pratyush Anand <panand@redhat.com>
>> ---
>>   arch/arm/kernel/uprobes.c |  6 ------
>>   kernel/events/uprobes.c   | 18 ++++++++++++++++++
>>   2 files changed, 18 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm/kernel/uprobes.c b/arch/arm/kernel/uprobes.c
>> index 56adf9c1fde0..0f3663ca82fc 100644
>> --- a/arch/arm/kernel/uprobes.c
>> +++ b/arch/arm/kernel/uprobes.c
>> @@ -178,12 +178,6 @@ void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
>>   	instruction_pointer_set(regs, utask->vaddr);
>>   }
>>
>> -int arch_uprobe_exception_notify(struct notifier_block *self,
>> -				 unsigned long val, void *data)
>> -{
>> -	return NOTIFY_DONE;
>> -}
>
> I agree, this is ugly. But I disagree with this change.
>
> I think we should simply kill uprobe_exception_nb and unexport
> arch_uprobe_exception_notify on x86/powerpc, and in fact I was going to do
> this a long ago.
>
> I'll send the patch later. Until then please add the dummy arch_uprobe_exception_notify()
> like arch/arm does, to make the generic code happy.

OK.

~Pratyush
>
> Oleg.
>

[RFC 5/8] ARM64: Re-factor flush_ptrace_access

[Pratyush Anand]

On Friday 02 January 2015 11:49 PM, Oleg Nesterov wrote:
> On 01/02, Oleg Nesterov wrote:
>>
>> On 12/31, Pratyush Anand wrote:
>>>
>>> Re-factor flush_ptrace_access to reuse vma independent part.
>>
>> But for what? The changelog should explain this.
>>
>>> Signed-off-by: Pratyush Anand <panand@redhat.com>
>>> ---
>>>   arch/arm64/mm/flush.c | 24 +++++++++++++++---------
>>>   1 file changed, 15 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
>>> index b6f14e8d2121..9a4dd6f39cfb 100644
>>> --- a/arch/arm64/mm/flush.c
>>> +++ b/arch/arm64/mm/flush.c
>>> @@ -34,19 +34,25 @@ void flush_cache_range(struct vm_area_struct *vma, unsigned long start,
>>>   		__flush_icache_all();
>>>   }
>>>
>>> +static void __flush_ptrace_access(struct page *page, unsigned long uaddr,
>>> +		void *kaddr, unsigned long len)
>>> +{
>>> +	unsigned long addr = (unsigned long)kaddr;
>>> +
>>> +	if (icache_is_aliasing()) {
>>> +		__flush_dcache_area(kaddr, len);
>>> +		__flush_icache_all();
>>> +	} else {
>>> +		flush_icache_range(addr, addr + len);
>>> +	}
>>> +}
>>> +
>>>   static void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
>>>   				unsigned long uaddr, void *kaddr,
>>>   				unsigned long len)
>>>   {
>>> -	if (vma->vm_flags & VM_EXEC) {
>>> -		unsigned long addr = (unsigned long)kaddr;
>>> -		if (icache_is_aliasing()) {
>>> -			__flush_dcache_area(kaddr, len);
>>> -			__flush_icache_all();
>>> -		} else {
>>> -			flush_icache_range(addr, addr + len);
>>> -		}
>>> -	}
>>> +	if (vma->vm_flags & VM_EXEC)
>>> +		__flush_ptrace_access(page, uaddr, kaddr, len);
>>>   }
>>
>> So why uprobes can't use flush_ptrace_access() ? flush_uprobe_xol_access() is
>> called by arch_uprobe_copy_ixol(), and xol vma has VM_EXEC bit set.
>
> Ah, sorry, I forgot that arch_uprobe_copy_ixol() doesn't have "vma" so it
> can't use flush_ptrace_access()... perhaps you can update the changelog.
>

OK.. Will improve commit log.

~Pratyush
> Oleg.
>

[RFC 8/8] ARM64: Add uprobe support

[Oleg Nesterov]

On 01/04, Pratyush Anand wrote:
>
> On Friday 02 January 2015 10:53 PM, Oleg Nesterov wrote:
>> But the main question is: why do we need add/find_ss_context ?? Please
>> explain.
>>
>
> See arch/arm64/kernel/debug-monitors.c: call_step_hook
>
> Unlike breakpoint exception, there is no ESR info check for step
> exception. So, it is the responsibility of step handler
> (uprobe_single_step_handler) to make sure that exception was generated
> for it.

Yes, yes, this is clear. My point was, we can (I think) rely on
uprobe_post_sstep_notifier() which checks ->active_uprobe != NULL.

And I guess you understood what I meant, but since I wasn't clear let
me repeat to ensure we really understand each other.

Can't

	uprobe_single_step_handler(regs, esr)
	{
		if (user_mode(regs) && uprobe_post_sstep_notifier(regs))
			return HANDLED;
		return ERROR;
	}

work without this step_ctx logic?

If everything is correct, the probed task can execute a single (xol) insn
in user-mode before the trap. If ->active_uprobe is set we know that we
expect the ss trap in user-mode, and nothing else except this xol insn can
generate it?

Perhaps arm64 needs additional checks, I dunno... If you think that the
->active_uprobe check is not enough you can probably also verify that
"utask->state = UTASK_SSTEP" and/or "regs->pc - 4 == utask->xol_vaddr",
but so far it seems to me that these additional checks can only make sense
under WARN_ON().

Oleg.

[RFC 8/8] ARM64: Add uprobe support

[Pratyush Anand]

On Monday 05 January 2015 12:10 AM, Oleg Nesterov wrote:
> On 01/04, Pratyush Anand wrote:
>>
>> On Friday 02 January 2015 10:53 PM, Oleg Nesterov wrote:
>>> But the main question is: why do we need add/find_ss_context ?? Please
>>> explain.
>>>
>>
>> See arch/arm64/kernel/debug-monitors.c: call_step_hook
>>
>> Unlike breakpoint exception, there is no ESR info check for step
>> exception. So, it is the responsibility of step handler
>> (uprobe_single_step_handler) to make sure that exception was generated
>> for it.
>
> Yes, yes, this is clear. My point was, we can (I think) rely on
> uprobe_post_sstep_notifier() which checks ->active_uprobe != NULL.
>
> And I guess you understood what I meant, but since I wasn't clear let
> me repeat to ensure we really understand each other.
>
> Can't
>
> 	uprobe_single_step_handler(regs, esr)
> 	{
> 		if (user_mode(regs) && uprobe_post_sstep_notifier(regs))
> 			return HANDLED;
> 		return ERROR;
> 	}
>
> work without this step_ctx logic?
>

Yes,yes, no need of step_ctx logic.

> If everything is correct, the probed task can execute a single (xol) insn
> in user-mode before the trap. If ->active_uprobe is set we know that we
> expect the ss trap in user-mode, and nothing else except this xol insn can
> generate it?

Yes, I do see any value addition in saving xol_vaddr in ss_ctx->match_addr.

>
> Perhaps arm64 needs additional checks, I dunno... If you think that the
> ->active_uprobe check is not enough you can probably also verify that
> "utask->state = UTASK_SSTEP" and/or "regs->pc - 4 == utask->xol_vaddr",
> but so far it seems to me that these additional checks can only make sense
> under WARN_ON().

Yes.

~Pratyush

[RFC 1/8] ARM64: Move BRK opcodes defines from kprobes.h to insn.h

[Will Deacon]

On Wed, Dec 31, 2014 at 03:21:17PM +0000, Pratyush Anand wrote:
> Its better to keep all BRK opcodes used by kprobes and uprobes at one
> place. Therefore move these defines to asm/insn.h.
> 
> Signed-off-by: Pratyush Anand <panand@redhat.com>
> ---
>  arch/arm64/include/asm/insn.h | 6 ++++++
>  arch/arm64/kernel/kprobes.h   | 7 +------
>  2 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
> index e2ff32a93b5c..87fa48746806 100644
> --- a/arch/arm64/include/asm/insn.h
> +++ b/arch/arm64/include/asm/insn.h
> @@ -23,6 +23,12 @@
>  /* A64 instructions are always 32 bits. */
>  #define	AARCH64_INSN_SIZE		4
>  
> +/* BRK opcodes with ESR encoding  */
> +#define BRK64_ESR_MASK		0xFFFF
> +#define BRK64_ESR_KPROBES	0x0004
> +#define BRK64_OPCODE_KPROBES	0xD4200080	/* "brk 0x4" */

These might be better off in debug-monitors.h, but I guess that's for the
kprobes series to sort out.

> +#define ARCH64_NOP_OPCODE	0xD503201F

We have aarch64_insn_gen_nop for this.

Will

[RFC 2/8] ARM64: Refactor kprobes-arm64

[Will Deacon]

On Wed, Dec 31, 2014 at 03:21:18PM +0000, Pratyush Anand wrote:
> Most of the stuff of kprobes-arm64.c can also be used by uprobes.c. So
> move all those part to common code area. In the process rename kprobe to
> probe whereever possible.
> 
> No functional change.

In which case, can you merge this into the kprobes series (which we haven't
merged yet)?

Will

[RFC 4/8] ARM64: Add instruction_pointer_set function

[Will Deacon]

On Wed, Dec 31, 2014 at 03:21:20PM +0000, Pratyush Anand wrote:
> instruction_pointer_set is needed for uprobe implementation. Hence
> define it for ARM64.
> 
> Signed-off-by: Pratyush Anand <panand@redhat.com>
> ---
>  arch/arm64/include/asm/ptrace.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
> index 24cc048ac3e7..29d9bf5e3635 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -206,6 +206,12 @@ static inline int valid_user_regs(struct user_pt_regs *regs)
>  #define instruction_pointer(regs)	((regs)->pc)
>  #define stack_pointer(regs)		((regs)->sp)
>  
> +static inline void instruction_pointer_set(struct pt_regs *regs,
> +					   unsigned long val)
> +{
> +	instruction_pointer(regs) = val;
> +}

Do you think we could make use of the asm-generic ptrace header to get
this for free? afaict, we just need to implement GET_USP and possibly
GET_FP for the compat case (although it may well be that we still handle
the compat case entirely separately).

Will

[RFC 6/8] ARM64: Handle TRAP_HWBRKPT for user mode as well

[Will Deacon]

On Fri, Jan 02, 2015 at 06:05:23PM +0000, Oleg Nesterov wrote:
> Let me repeat once again that I know absolutely nothing about arm* ;)
> 
> On 12/31, Pratyush Anand wrote:
> >
> > uprobe registers a handler at step_hook. So, single_step_handler now
> > checks for user mode as well if there is a valid hook.
> >
> > Signed-off-by: Pratyush Anand <panand@redhat.com>
> > ---
> >  arch/arm64/kernel/debug-monitors.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
> > index b056369fd47d..2676b8655241 100644
> > --- a/arch/arm64/kernel/debug-monitors.c
> > +++ b/arch/arm64/kernel/debug-monitors.c
> > @@ -236,6 +236,9 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
> >  	if (!reinstall_suspended_bps(regs))
> >  		return 0;
> >
> > +	if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
> > +		return 0;
> > +
> >  	if (user_mode(regs)) {
> >  		info.si_signo = SIGTRAP;
> >  		info.si_errno = 0;
> > @@ -251,9 +254,6 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
> >  		 */
> >  		user_rewind_single_step(current);
> >  	} else {
> > -		if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
> > -			return 0;
> > -
> 
> Agreed, we need something like this change...
> 
> But did you verify that it can't break other users of register_step_hook() ?
> The current handlers do not check user_mode() == F, they assume that they
> can't be called otherwise.
> 
> If this all is correct, please explain why in the changelog.

I think you're right, and kgdb will need fixing with this change.

Will

[RFC 8/8] ARM64: Add uprobe support

[Will Deacon]

On Wed, Dec 31, 2014 at 03:21:24PM +0000, Pratyush Anand wrote:
> This patch adds support for uprobe on ARM64 architecture.
> 
> Unit test for following has been done so far and they have been found
> working
> 1. Normal instruction, which can be probed like sub, ldr, add etc.
> 2. Instructions which can be simulated like ret.
> 3. uretprobe

I'm assuming that means you don't support compat (AArch32) tasks with this?
How do you enforce that?

Will

[RFC 1/8] ARM64: Move BRK opcodes defines from kprobes.h to insn.h

[Pratyush Anand]

On Thursday 08 January 2015 10:25 PM, Will Deacon wrote:
> On Wed, Dec 31, 2014 at 03:21:17PM +0000, Pratyush Anand wrote:
>> Its better to keep all BRK opcodes used by kprobes and uprobes at one
>> place. Therefore move these defines to asm/insn.h.
>>
>> Signed-off-by: Pratyush Anand <panand@redhat.com>
>> ---
>>   arch/arm64/include/asm/insn.h | 6 ++++++
>>   arch/arm64/kernel/kprobes.h   | 7 +------
>>   2 files changed, 7 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
>> index e2ff32a93b5c..87fa48746806 100644
>> --- a/arch/arm64/include/asm/insn.h
>> +++ b/arch/arm64/include/asm/insn.h
>> @@ -23,6 +23,12 @@
>>   /* A64 instructions are always 32 bits. */
>>   #define	AARCH64_INSN_SIZE		4
>>
>> +/* BRK opcodes with ESR encoding  */
>> +#define BRK64_ESR_MASK		0xFFFF
>> +#define BRK64_ESR_KPROBES	0x0004
>> +#define BRK64_OPCODE_KPROBES	0xD4200080	/* "brk 0x4" */
>
> These might be better off in debug-monitors.h, but I guess that's for the
> kprobes series to sort out.
>

Agreed.

~Pratyush
>> +#define ARCH64_NOP_OPCODE	0xD503201F
>
> We have aarch64_insn_gen_nop for this.
>
> Will
>

[RFC 2/8] ARM64: Refactor kprobes-arm64

[Pratyush Anand]

On Thursday 08 January 2015 10:25 PM, Will Deacon wrote:
> On Wed, Dec 31, 2014 at 03:21:18PM +0000, Pratyush Anand wrote:
>> Most of the stuff of kprobes-arm64.c can also be used by uprobes.c. So
>> move all those part to common code area. In the process rename kprobe to
>> probe whereever possible.
>>
>> No functional change.
>
> In which case, can you merge this into the kprobes series (which we haven't
> merged yet)?
>

Yes, thats why these are just RFCs. I will send next version of uprobe 
only after kprobe patches are accepted into maintainer's tree.

~Pratyush

> Will
> --
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>

[RFC 2/8] ARM64: Refactor kprobes-arm64

[Will Deacon]

On Thu, Jan 08, 2015 at 05:33:08PM +0000, Pratyush Anand wrote:
> On Thursday 08 January 2015 10:25 PM, Will Deacon wrote:
> > On Wed, Dec 31, 2014 at 03:21:18PM +0000, Pratyush Anand wrote:
> >> Most of the stuff of kprobes-arm64.c can also be used by uprobes.c. So
> >> move all those part to common code area. In the process rename kprobe to
> >> probe whereever possible.
> >>
> >> No functional change.
> >
> > In which case, can you merge this into the kprobes series (which we haven't
> > merged yet)?
> >
> 
> Yes, thats why these are just RFCs. I will send next version of uprobe 
> only after kprobe patches are accepted into maintainer's tree.

Ok, but it also makes sense to make kprobes refactoring changes *before* the
patches are merged, as that reduces churn in mainline whilst you don't have
any other dependencies.

Will

[RFC 2/8] ARM64: Refactor kprobes-arm64

[Pratyush Anand]

On Thursday 08 January 2015 11:06 PM, Will Deacon wrote:
> On Thu, Jan 08, 2015 at 05:33:08PM +0000, Pratyush Anand wrote:
>> On Thursday 08 January 2015 10:25 PM, Will Deacon wrote:
>>> On Wed, Dec 31, 2014 at 03:21:18PM +0000, Pratyush Anand wrote:
>>>> Most of the stuff of kprobes-arm64.c can also be used by uprobes.c. So
>>>> move all those part to common code area. In the process rename kprobe to
>>>> probe whereever possible.
>>>>
>>>> No functional change.
>>>
>>> In which case, can you merge this into the kprobes series (which we haven't
>>> merged yet)?
>>>
>>
>> Yes, thats why these are just RFCs. I will send next version of uprobe
>> only after kprobe patches are accepted into maintainer's tree.
>
> Ok, but it also makes sense to make kprobes refactoring changes *before* the
> patches are merged, as that reduces churn in mainline whilst you don't have
> any other dependencies.
>

Sure, Sure.. I too expect first two patches to be merged with kprobe 
series. I just did that to develop my uprobe code.

~Pratyush

> Will
>

[RFC 6/8] ARM64: Handle TRAP_HWBRKPT for user mode as well

[Pratyush Anand]

On Thursday 08 January 2015 10:31 PM, Will Deacon wrote:
> On Fri, Jan 02, 2015 at 06:05:23PM +0000, Oleg Nesterov wrote:
>> Let me repeat once again that I know absolutely nothing about arm* ;)
>>
>> On 12/31, Pratyush Anand wrote:
>>>
>>> uprobe registers a handler at step_hook. So, single_step_handler now
>>> checks for user mode as well if there is a valid hook.
>>>
>>> Signed-off-by: Pratyush Anand <panand@redhat.com>
>>> ---
>>>   arch/arm64/kernel/debug-monitors.c | 6 +++---
>>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
>>> index b056369fd47d..2676b8655241 100644
>>> --- a/arch/arm64/kernel/debug-monitors.c
>>> +++ b/arch/arm64/kernel/debug-monitors.c
>>> @@ -236,6 +236,9 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
>>>   	if (!reinstall_suspended_bps(regs))
>>>   		return 0;
>>>
>>> +	if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
>>> +		return 0;
>>> +
>>>   	if (user_mode(regs)) {
>>>   		info.si_signo = SIGTRAP;
>>>   		info.si_errno = 0;
>>> @@ -251,9 +254,6 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
>>>   		 */
>>>   		user_rewind_single_step(current);
>>>   	} else {
>>> -		if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
>>> -			return 0;
>>> -
>>
>> Agreed, we need something like this change...
>>
>> But did you verify that it can't break other users of register_step_hook() ?
>> The current handlers do not check user_mode() == F, they assume that they
>> can't be called otherwise.
>>
>> If this all is correct, please explain why in the changelog.
>
> I think you're right, and kgdb will need fixing with this change.

OK, I will fix kgdb  too when I will send next revision.

~Pratyush

>
> Will
> --
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> Please read the FAQ at  http://www.tux.org/lkml/
>

[RFC 8/8] ARM64: Add uprobe support

[Pratyush Anand]

On Thursday 08 January 2015 10:33 PM, Will Deacon wrote:
> On Wed, Dec 31, 2014 at 03:21:24PM +0000, Pratyush Anand wrote:
>> This patch adds support for uprobe on ARM64 architecture.
>>
>> Unit test for following has been done so far and they have been found
>> working
>> 1. Normal instruction, which can be probed like sub, ldr, add etc.
>> 2. Instructions which can be simulated like ret.
>> 3. uretprobe
>
> I'm assuming that means you don't support compat (AArch32) tasks with this?

Hummm.. Yes, compat not yet supported.

I will come back on this.

~Pratyush

> How do you enforce that?
>
> Will
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>

[RFC 4/8] ARM64: Add instruction_pointer_set function

[Pratyush Anand]

On Thursday 08 January 2015 10:29 PM, Will Deacon wrote:
> On Wed, Dec 31, 2014 at 03:21:20PM +0000, Pratyush Anand wrote:
>> instruction_pointer_set is needed for uprobe implementation. Hence
>> define it for ARM64.
>>
>> Signed-off-by: Pratyush Anand <panand@redhat.com>
>> ---
>>   arch/arm64/include/asm/ptrace.h | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
>> index 24cc048ac3e7..29d9bf5e3635 100644
>> --- a/arch/arm64/include/asm/ptrace.h
>> +++ b/arch/arm64/include/asm/ptrace.h
>> @@ -206,6 +206,12 @@ static inline int valid_user_regs(struct user_pt_regs *regs)
>>   #define instruction_pointer(regs)	((regs)->pc)
>>   #define stack_pointer(regs)		((regs)->sp)
>>
>> +static inline void instruction_pointer_set(struct pt_regs *regs,
>> +					   unsigned long val)
>> +{
>> +	instruction_pointer(regs) = val;
>> +}
>
> Do you think we could make use of the asm-generic ptrace header to get
> this for free? afaict, we just need to implement GET_USP and possibly
> GET_FP for the compat case (although it may well be that we still handle
> the compat case entirely separately).
>

Yes, We can use asm-generic for it.

I think , we can also add link_pointer and link_pointer_set in 
asm-generic/ptrace.h to help with all retprobes.

~Pratyush
> Will
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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> Please read the FAQ at  http://www.tux.org/lkml/
>

[RFC 8/8] ARM64: Add uprobe support

[Oleg Nesterov]

On 01/08, Pratyush Anand wrote:
>
> On Thursday 08 January 2015 10:33 PM, Will Deacon wrote:
>>
>> I'm assuming that means you don't support compat (AArch32) tasks with this?
>
> Hummm.. Yes, compat not yet supported.
>
> I will come back on this.

I obviously do not know how difficult is to support the compat tasks, and
in any case I leave this to you and Will.

But if this is not simple, perhaps the initial implementation could simply
nack the probe in arch_uprobe_analyze_insn() if this mm is not 64-bit.
Although I do not see something like is_64bit_mm() in arch/arm64... So may be
the first version can even ignore this problem and just document the fact
that AArch32 tasks are not supported.

Oleg.

[RFC 8/8] ARM64: Add uprobe support

[Oleg Nesterov]

On 12/31, Pratyush Anand wrote:
>
> +int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
> +		unsigned long addr)
> +{
> +	probe_opcode_t insn;
> +
> +	insn = *(probe_opcode_t *)(&auprobe->insn[0]);
> +
> +	switch (arm_probe_decode_insn(insn, &auprobe->ainsn)) {
> +	case INSN_REJECTED:
> +		return -EINVAL;
> +
> +	case INSN_GOOD_NO_SLOT:
> +		auprobe->simulate = true;
> +		if (auprobe->ainsn.prepare)
> +			auprobe->ainsn.prepare(insn, &auprobe->ainsn);
> +		break;
> +
> +	case INSN_GOOD:
> +	default:
> +		break;
> +	}
> +
> +	return 0;
> +}

forgot to mention... shouldn't it also check IS_ALIGNED(addr, AARCH64_INSN_SIZE) ?

I do not know if unaligned insn address is valid on arm64 or not, but please
note that at least it should not cross the page boundary, set_swbp() needs to
write AARCH64_INSN_SIZE == UPROBE_SWBP_INSN bytes and it assumes that this
should fit the single page.

Oleg.

[RFC 8/8] ARM64: Add uprobe support

[Pratyush Anand]

On Friday 09 January 2015 11:15 PM, Oleg Nesterov wrote:
> On 01/08, Pratyush Anand wrote:
>>
>> On Thursday 08 January 2015 10:33 PM, Will Deacon wrote:
>>>
>>> I'm assuming that means you don't support compat (AArch32) tasks with this?
>>
>> Hummm.. Yes, compat not yet supported.
>>
>> I will come back on this.
>
> I obviously do not know how difficult is to support the compat tasks, and
> in any case I leave this to you and Will.
>

I think most of the stuff can be picked from arch/arm. But I do not have 
a platform to test this feature.So, I will not be taking up as of now.

~Pratyush

[RFC 8/8] ARM64: Add uprobe support

[Pratyush Anand]

On Friday 09 January 2015 11:29 PM, Oleg Nesterov wrote:
> On 12/31, Pratyush Anand wrote:
>>
>> +int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
>> +		unsigned long addr)
>> +{
>> +	probe_opcode_t insn;
>> +
>> +	insn = *(probe_opcode_t *)(&auprobe->insn[0]);
>> +
>> +	switch (arm_probe_decode_insn(insn, &auprobe->ainsn)) {
>> +	case INSN_REJECTED:
>> +		return -EINVAL;
>> +
>> +	case INSN_GOOD_NO_SLOT:
>> +		auprobe->simulate = true;
>> +		if (auprobe->ainsn.prepare)
>> +			auprobe->ainsn.prepare(insn, &auprobe->ainsn);
>> +		break;
>> +
>> +	case INSN_GOOD:
>> +	default:
>> +		break;
>> +	}
>> +
>> +	return 0;
>> +}
>
> forgot to mention... shouldn't it also check IS_ALIGNED(addr, AARCH64_INSN_SIZE) ?
>
> I do not know if unaligned insn address is valid on arm64 or not, but please

AARCH64 instructions are always of fixed lenght ie 4 bytes. I do not see 
possibility of addr being unaligned. Please let me know, if I am missing 
something.

> note that at least it should not cross the page boundary, set_swbp() needs to
> write AARCH64_INSN_SIZE == UPROBE_SWBP_INSN bytes and it assumes that this
> should fit the single page.

So, again I do not see the possibility of crossing of page boundary for 
any instruction address.

~Pratyush

[RFC 8/8] ARM64: Add uprobe support

[Pratyush Anand]

Hi Oleg,

How can I generate a scenario to test:

a) arch_uprobe_xol_was_trapped
b) arch_uprobe_abort_xol

~Pratyush

On Monday 12 January 2015 10:34 AM, Pratyush Anand wrote:
>
>
> On Friday 09 January 2015 11:29 PM, Oleg Nesterov wrote:
>> On 12/31, Pratyush Anand wrote:
>>>
>>> +int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct
>>> mm_struct *mm,
>>> +        unsigned long addr)
>>> +{
>>> +    probe_opcode_t insn;
>>> +
>>> +    insn = *(probe_opcode_t *)(&auprobe->insn[0]);
>>> +
>>> +    switch (arm_probe_decode_insn(insn, &auprobe->ainsn)) {
>>> +    case INSN_REJECTED:
>>> +        return -EINVAL;
>>> +
>>> +    case INSN_GOOD_NO_SLOT:
>>> +        auprobe->simulate = true;
>>> +        if (auprobe->ainsn.prepare)
>>> +            auprobe->ainsn.prepare(insn, &auprobe->ainsn);
>>> +        break;
>>> +
>>> +    case INSN_GOOD:
>>> +    default:
>>> +        break;
>>> +    }
>>> +
>>> +    return 0;
>>> +}
>>
>> forgot to mention... shouldn't it also check IS_ALIGNED(addr,
>> AARCH64_INSN_SIZE) ?
>>
>> I do not know if unaligned insn address is valid on arm64 or not, but
>> please
>
> AARCH64 instructions are always of fixed lenght ie 4 bytes. I do not see
> possibility of addr being unaligned. Please let me know, if I am missing
> something.
>
>> note that at least it should not cross the page boundary, set_swbp()
>> needs to
>> write AARCH64_INSN_SIZE == UPROBE_SWBP_INSN bytes and it assumes that
>> this
>> should fit the single page.
>
> So, again I do not see the possibility of crossing of page boundary for
> any instruction address.
>
> ~Pratyush

[RFC 8/8] ARM64: Add uprobe support

[Oleg Nesterov]

On 01/12, Pratyush Anand wrote:
>
>
> On Friday 09 January 2015 11:29 PM, Oleg Nesterov wrote:
>> On 12/31, Pratyush Anand wrote:
>>>
>>> +int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
>>> +		unsigned long addr)
>>> +{
>>> +	probe_opcode_t insn;
>>> +
>>> +	insn = *(probe_opcode_t *)(&auprobe->insn[0]);
>>> +
>>> +	switch (arm_probe_decode_insn(insn, &auprobe->ainsn)) {
>>> +	case INSN_REJECTED:
>>> +		return -EINVAL;
>>> +
>>> +	case INSN_GOOD_NO_SLOT:
>>> +		auprobe->simulate = true;
>>> +		if (auprobe->ainsn.prepare)
>>> +			auprobe->ainsn.prepare(insn, &auprobe->ainsn);
>>> +		break;
>>> +
>>> +	case INSN_GOOD:
>>> +	default:
>>> +		break;
>>> +	}
>>> +
>>> +	return 0;
>>> +}
>>
>> forgot to mention... shouldn't it also check IS_ALIGNED(addr, AARCH64_INSN_SIZE) ?
>>
>> I do not know if unaligned insn address is valid on arm64 or not, but please
>
> AARCH64 instructions are always of fixed lenght ie 4 bytes. I do not see
> possibility of addr being unaligned. Please let me know, if I am missing
> something.

A user can write any offset into uprobe_events, and the generic code doesn't
check it is aligned.

>> note that at least it should not cross the page boundary, set_swbp() needs to
>> write AARCH64_INSN_SIZE == UPROBE_SWBP_INSN bytes and it assumes that this
>> should fit the single page.
>
> So, again I do not see the possibility of crossing of page boundary for
> any instruction address.

See above. So yes, it should really check IS_ALIGNED(AARCH64_INSN_SIZE).

Oleg.

[RFC 8/8] ARM64: Add uprobe support

[Oleg Nesterov]

On 01/12, Pratyush Anand wrote:
>
> Hi Oleg,
>
> How can I generate a scenario to test:
>
> a) arch_uprobe_xol_was_trapped
> b) arch_uprobe_abort_xol

For example, you can probe something like

	*(int *)NULL = 0;

See also the x86 test-case in https://lkml.org/lkml/2011/10/21/148
and the whole thread.

Oleg.