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From: James Morse <james.morse@arm.com>
To: Pratyush Anand <panand@redhat.com>
Cc: "David Long" <dave.long@linaro.org>,
	"Will Deacon" <will.deacon@arm.com>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Sandeepa Prabhu" <sandeepa.s.prabhu@gmail.com>,
	"William Cohen" <wcohen@redhat.com>,
	"Steve Capper" <steve.capper@linaro.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	"Marc Zyngier" <marc.zyngier@arm.com>,
	"Dave P Martin" <Dave.Martin@arm.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Robin Murphy" <Robin.Murphy@arm.com>,
	"Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
	"Jens Wiklander" <jens.wiklander@linaro.org>,
	"Christoffer Dall" <christoffer.dall@linaro.org>,
	"Alex Bennée" <alex.bennee@linaro.org>,
	"Yang Shi" <yang.shi@linaro.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	"Suzuki K. Poulose" <suzuki.poulose@arm.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Zi Shen Lim" <zlim.lnx@gmail.com>,
	"John Blackwood" <john.blackwood@ccur.com>,
	"Feng Kan" <fkan@apm.com>,
	"Balamurugan Shanmugam" <bshanmugam@apm.com>,
	"Vladimir Murzin" <Vladimir.Murzin@arm.com>,
	"Mark Salyzyn" <salyzyn@android.com>,
	"Petr Mladek" <pmladek@suse.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Mark Brown" <broonie@kernel.org>
Subject: Re: [PATCH v11 3/9] arm64: add copy_to/from_user to kprobes blacklist
Date: Fri, 18 Mar 2016 18:12:20 +0000	[thread overview]
Message-ID: <56EC4504.6060702@arm.com> (raw)
In-Reply-To: <20160318144325.GB29225@dhcppc6.redhat.com>

Hi Pratyush,

On 18/03/16 14:43, Pratyush Anand wrote:
> On 18/03/2016:02:02:49 PM, James Morse wrote:
>> In kernel/entry.S when entered from EL0 we test for TIF_SINGLESTEP in the
>> thread_info flags, and use disable_step_tsk/enable_step_tsk to save/restore the
>> single-step state.
>>
>> Could we do this regardless of which EL we came from?
> 
> Thanks for another idea. I think, we can not do this as it is, because
> TIF_SINGLESTEP will not be set for kprobe events.

Hmmm, I see kernel_enable_single_step() doesn't set it, but setup_singlestep()
in patch 5 could...

There is probably a good reason its never set for a kernel thread, I will have a
look at where else it is used.


> But, we can introduce a
> variant disable_step_kernel and enable_step_kernel, which can be called in
> el1_da. 

What about sp/pc misalignment, or undefined instructions?
Or worse... an irq occurs during your el1_da call (el1_da may re-enable irqs).
el1_irq doesn't know you were careful not to unmask debug exceptions, it blindly
turns them back on.

The problem is the 'single step me' bit is still set, save/restoring it will
save us having to consider every interaction, (and then missing some!).

It would also mean you don't have to disable interrupts while single stepping in
patch 5 (comment above kprobes_save_local_irqflag()).


Thanks,

James

WARNING: multiple messages have this Message-ID (diff)
From: james.morse@arm.com (James Morse)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v11 3/9] arm64: add copy_to/from_user to kprobes blacklist
Date: Fri, 18 Mar 2016 18:12:20 +0000	[thread overview]
Message-ID: <56EC4504.6060702@arm.com> (raw)
In-Reply-To: <20160318144325.GB29225@dhcppc6.redhat.com>

Hi Pratyush,

On 18/03/16 14:43, Pratyush Anand wrote:
> On 18/03/2016:02:02:49 PM, James Morse wrote:
>> In kernel/entry.S when entered from EL0 we test for TIF_SINGLESTEP in the
>> thread_info flags, and use disable_step_tsk/enable_step_tsk to save/restore the
>> single-step state.
>>
>> Could we do this regardless of which EL we came from?
> 
> Thanks for another idea. I think, we can not do this as it is, because
> TIF_SINGLESTEP will not be set for kprobe events.

Hmmm, I see kernel_enable_single_step() doesn't set it, but setup_singlestep()
in patch 5 could...

There is probably a good reason its never set for a kernel thread, I will have a
look at where else it is used.


> But, we can introduce a
> variant disable_step_kernel and enable_step_kernel, which can be called in
> el1_da. 

What about sp/pc misalignment, or undefined instructions?
Or worse... an irq occurs during your el1_da call (el1_da may re-enable irqs).
el1_irq doesn't know you were careful not to unmask debug exceptions, it blindly
turns them back on.

The problem is the 'single step me' bit is still set, save/restoring it will
save us having to consider every interaction, (and then missing some!).

It would also mean you don't have to disable interrupts while single stepping in
patch 5 (comment above kprobes_save_local_irqflag()).


Thanks,

James

  reply	other threads:[~2016-03-18 18:13 UTC|newest]

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-09  5:32 [PATCH v11 0/9] arm64: Add kernel probes (kprobes) support David Long
2016-03-09  5:32 ` David Long
2016-03-09  5:32 ` [PATCH v11 1/9] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature David Long
2016-03-09  5:32   ` David Long
2016-03-11 18:07   ` James Morse
2016-03-11 18:07     ` James Morse
2016-03-18 13:06     ` David Long
2016-03-18 13:06       ` David Long
2016-03-15 11:04   ` Marc Zyngier
2016-03-15 11:04     ` Marc Zyngier
2016-03-21  7:08     ` David Long
2016-03-21  7:08       ` David Long
2016-03-09  5:32 ` [PATCH v11 2/9] arm64: Add more test functions to insn.c David Long
2016-03-09  5:32   ` David Long
2016-03-09  5:32 ` [PATCH v11 3/9] arm64: add copy_to/from_user to kprobes blacklist David Long
2016-03-09  5:32   ` David Long
2016-03-15 18:47   ` James Morse
2016-03-15 18:47     ` James Morse
2016-03-16  5:43     ` Pratyush Anand
2016-03-16  5:43       ` Pratyush Anand
2016-03-16 10:27       ` James Morse
2016-03-16 10:27         ` James Morse
2016-03-17  7:57         ` Pratyush Anand
2016-03-17  7:57           ` Pratyush Anand
2016-03-18 13:29           ` Pratyush Anand
2016-03-18 13:29             ` Pratyush Anand
2016-03-18 14:02             ` James Morse
2016-03-18 14:02               ` James Morse
2016-03-18 14:43               ` Pratyush Anand
2016-03-18 14:43                 ` Pratyush Anand
2016-03-18 18:12                 ` James Morse [this message]
2016-03-18 18:12                   ` James Morse
2016-03-21  5:17                   ` Pratyush Anand
2016-03-21  5:17                     ` Pratyush Anand
2016-03-21 14:52             ` Will Deacon
2016-03-21 14:52               ` Will Deacon
2016-03-22 16:51               ` Pratyush Anand
2016-03-22 16:51                 ` Pratyush Anand
2016-03-17 12:04   ` 平松雅巳 / HIRAMATU，MASAMI
2016-03-17 12:04     ` 平松雅巳 / HIRAMATU，MASAMI
2016-03-09  5:32 ` [PATCH v11 4/9] arm64: add conditional instruction simulation support David Long
2016-03-09  5:32   ` David Long
2016-03-13 12:09   ` Marc Zyngier
2016-03-13 12:09     ` Marc Zyngier
2016-03-14  4:04     ` Pratyush Anand
2016-03-14  4:04       ` Pratyush Anand
2016-03-14  7:38       ` Marc Zyngier
2016-03-14  7:38         ` Marc Zyngier
2016-03-21  8:35         ` David Long
2016-03-21  8:35           ` David Long
2016-03-09  5:32 ` [PATCH v11 5/9] arm64: Kprobes with single stepping support David Long
2016-03-09  5:32   ` David Long
2016-04-20  1:29   ` Li Bin
2016-04-20  1:29     ` Li Bin
2016-03-09  5:32 ` [PATCH v11 6/9] arm64: kprobes instruction simulation support David Long
2016-03-09  5:32   ` David Long
2016-03-12  3:56   ` Marc Zyngier
2016-03-12  3:56     ` Marc Zyngier
2016-03-21  9:39     ` David Long
2016-03-21  9:39       ` David Long
2016-03-09  5:32 ` [PATCH v11 7/9] arm64: Add trampoline code for kretprobes David Long
2016-03-09  5:32   ` David Long
2016-03-13 13:52   ` Marc Zyngier
2016-03-13 13:52     ` Marc Zyngier
2016-03-21 13:30     ` David Long
2016-03-21 13:30       ` David Long
2016-03-09  5:32 ` [PATCH v11 8/9] arm64: Add kernel return probes support (kretprobes) David Long
2016-03-09  5:32   ` David Long
2016-03-17 12:22   ` 平松雅巳 / HIRAMATU，MASAMI
2016-03-17 12:22     ` 平松雅巳 / HIRAMATU，MASAMI
2016-03-17 12:58     ` 平松雅巳 / HIRAMATU，MASAMI
2016-03-17 12:58       ` 平松雅巳 / HIRAMATU，MASAMI
2016-03-21 13:33       ` David Long
2016-03-21 13:33         ` David Long
2016-03-09  5:32 ` [PATCH v11 9/9] kprobes: Add arm64 case in kprobe example module David Long
2016-03-09  5:32   ` David Long

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