Re: [RFC PATCH 1/1] arm64: implement live patching

From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
To: "nobuta.keiya@fujitsu.com" <nobuta.keiya@fujitsu.com>,
	Suraj Jitindar Singh <surajjs@amazon.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"live-patching@vger.kernel.org" <live-patching@vger.kernel.org>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"will@kernel.org" <will@kernel.org>,
	"mark.rutland@arm.com" <mark.rutland@arm.com>,
	"broonie@kernel.org" <broonie@kernel.org>,
	"duwe@lst.de" <duwe@lst.de>,
	"sjitindarsingh@gmail.com" <sjitindarsingh@gmail.com>,
	"benh@kernel.crashing.org" <benh@kernel.crashing.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC PATCH 1/1] arm64: implement live patching
Date: Thu, 17 Jun 2021 13:32:08 -0500	[thread overview]
Message-ID: <7080d2a9-6ec2-94e9-3577-e5f7233ad3ab@linux.microsoft.com> (raw)
In-Reply-To: <TYAPR01MB526348C06BB8E410DF8CE3D3850E9@TYAPR01MB5263.jpnprd01.prod.outlook.com>

On 6/17/21 4:29 AM, nobuta.keiya@fujitsu.com wrote:
> 
>> It's my understanding that the two pieces of work required to enable live
>> patching on arm are in flight upstream;
>> - Reliable stack traces as implemented by Madhavan T. Venkataraman [1]
>> - Objtool as implemented by Julien Thierry [2]
>>
>> This is the remaining part required to enable live patching on arm.
>> Based on work by Torsten Duwe [3]
>>
>> Allocate a task flag used to represent the patch pending state for the
>> task. Also implement generic functions klp_arch_set_pc() &
>> klp_get_ftrace_location().
>>
>> In klp_arch_set_pc() it is sufficient to set regs->pc as in
>> ftrace_common_return() the return address is loaded from the stack.
>>
>> ldr     x9, [sp, #S_PC]
>> <snip>
>> ret     x9
>>
>> In klp_get_ftrace_location() it is necessary to advance the address by
>> AARCH64_INSN_SIZE (4) to point to the BL in the callsite as 2 nops were
>> placed at the start of the function, one to be patched to save the LR and
>> another to be patched to branch to the ftrace call, and
>> klp_get_ftrace_location() is expected to return the address of the BL. It
>> may also be necessary to advance the address by another AARCH64_INSN_SIZE
>> if CONFIG_ARM64_BTI_KERNEL is enabled due to the instruction placed at the
>> branch target to satisfy BTI,
>>
>> Signed-off-by: Suraj Jitindar Singh <surajjs@amazon.com>
>>
>> [1] https://lkml.org/lkml/2021/5/26/1212
>> [2] https://lkml.org/lkml/2021/3/3/1135
>> [3] https://lkml.org/lkml/2018/10/26/536
>> ---
> 
> AFAIU Madhavan's patch series linked in the above [1] is currently awaiting
> review by Mark Rutland. It seems that not only this patch series but also the
> implementation of arch_stack_walk_reliable() at the below link is required
> to enable livepatch.
> 

Yes. I have a patch ready for that. But I can submit that only after the previous
series has been accepted.

Thanks

Madhavan

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