linux-kernel - Re: [PATCH v2 2/2] arm64: implement live patching

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Date:	Mon, 11 Jul 2016 16:03:08 +0200 (CEST)
From:	Miroslav Benes <mbenes@...e.cz>
To:	Torsten Duwe <duwe@....de>
cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>, takahiro.akashi@...aro.org,
	Jungseok Lee <jungseoklee85@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Li Bin <huawei.libin@...wei.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Christopher Li <sparse@...isli.org>,
	Jiri Kosina <jikos@...nel.org>, andrew.wafaa@....com,
	linux-arm-kernel@...ts.infradead.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	live-patching@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-sparse@...r.kernel.org, jeyu@...hat.com
Subject: Re: [PATCH v2 2/2] arm64: implement live patching

On Mon, 27 Jun 2016, Torsten Duwe wrote:

> diff --git a/arch/arm64/include/asm/livepatch.h b/arch/arm64/include/asm/livepatch.h
> new file mode 100644
> index 0000000..6b9a3d1
> --- /dev/null
> +++ b/arch/arm64/include/asm/livepatch.h
> @@ -0,0 +1,37 @@
> +/*
> + * livepatch.h - arm64-specific Kernel Live Patching Core
> + *
> + * Copyright (C) 2016 SUSE
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +#ifndef _ASM_ARM64_LIVEPATCH_H
> +#define _ASM_ARM64_LIVEPATCH_H
> +
> +#include <linux/module.h>
> +#include <linux/ftrace.h>
> +
> +#ifdef CONFIG_LIVEPATCH

A nit but we removed such guards in the other header files.

> +static inline int klp_check_compiler_support(void)
> +{
> +	return 0;
> +}
> +
> +static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
> +{
> +	regs->pc = ip;
> +}
> +#endif /* CONFIG_LIVEPATCH */

I also checked mod_arch_specific structure because of the way we deal 
with relocations. It is defined only if CONFIG_ARM64_MODULE_PLTS is 
enabled and there is a pointer to 'struct elf64_shdr' called plt. It is 
used indirectly in apply_relocate_add() so we need it to stay. However it 
points to an existing Elf section and SHF_ALLOC is added to its sh_flags 
in module_frob_arch_sections() (arch/arm64/kernel/module-plts.c). 
Therefore we should be ok.

Jessica, could you check it as well, please?

Thanks,
Miroslav