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From:   "nobuta.keiya@fujitsu.com" <nobuta.keiya@fujitsu.com>
To:     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>,
        "madvenka@linux.microsoft.com" <madvenka@linux.microsoft.com>,
        "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
Thread-Topic: [RFC PATCH 1/1] arm64: implement live patching
Thread-Index: AQHXWZ3CD4noxF06h0yjyXLanHsV4asX+OWg
Date:   Thu, 17 Jun 2021 09:29:22 +0000
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References: <20210604235930.603-1-surajjs@amazon.com>
In-Reply-To: <20210604235930.603-1-surajjs@amazon.com>
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=0A=
> It's my understanding that the two pieces of work required to enable live=
=0A=
> patching on arm are in flight upstream;=0A=
> - Reliable stack traces as implemented by Madhavan T. Venkataraman [1]=0A=
> - Objtool as implemented by Julien Thierry [2]=0A=
> =0A=
> This is the remaining part required to enable live patching on arm.=0A=
> Based on work by Torsten Duwe [3]=0A=
> =0A=
> Allocate a task flag used to represent the patch pending state for the=0A=
> task. Also implement generic functions klp_arch_set_pc() &=0A=
> klp_get_ftrace_location().=0A=
> =0A=
> In klp_arch_set_pc() it is sufficient to set regs->pc as in=0A=
> ftrace_common_return() the return address is loaded from the stack.=0A=
> =0A=
> ldr     x9, [sp, #S_PC]=0A=
> <snip>=0A=
> ret     x9=0A=
> =0A=
> In klp_get_ftrace_location() it is necessary to advance the address by=0A=
> AARCH64_INSN_SIZE (4) to point to the BL in the callsite as 2 nops were=
=0A=
> placed at the start of the function, one to be patched to save the LR and=
=0A=
> another to be patched to branch to the ftrace call, and=0A=
> klp_get_ftrace_location() is expected to return the address of the BL. It=
=0A=
> may also be necessary to advance the address by another AARCH64_INSN_SIZE=
=0A=
> if CONFIG_ARM64_BTI_KERNEL is enabled due to the instruction placed at th=
e=0A=
> branch target to satisfy BTI,=0A=
> =0A=
> Signed-off-by: Suraj Jitindar Singh <surajjs@amazon.com>=0A=
> =0A=
> [1] https://lkml.org/lkml/2021/5/26/1212=0A=
> [2] https://lkml.org/lkml/2021/3/3/1135=0A=
> [3] https://lkml.org/lkml/2018/10/26/536=0A=
> ---=0A=
=0A=
AFAIU Madhavan's patch series linked in the above [1] is currently awaiting=
=0A=
review by Mark Rutland. It seems that not only this patch series but also t=
he=0A=
implementation of arch_stack_walk_reliable() at the below link is required=
=0A=
to enable livepatch.=0A=
=0A=
https://lore.kernel.org/linux-arm-kernel/bf3a5289-8199-b665-0327-ed8240dd78=
27@linux.microsoft.com/=0A=
=0A=
=0A=
>  arch/arm64/Kconfig                   |  3 ++=0A=
>  arch/arm64/include/asm/livepatch.h   | 42 ++++++++++++++++++++++++++++=
=0A=
>  arch/arm64/include/asm/thread_info.h |  4 ++-=0A=
>  arch/arm64/kernel/signal.c           |  4 +++=0A=
>  4 files changed, 52 insertions(+), 1 deletion(-)=0A=
>  create mode 100644 arch/arm64/include/asm/livepatch.h=0A=
> =0A=
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig=0A=
> index b098dabed8c2..c4636990c01d 100644=0A=
> --- a/arch/arm64/Kconfig=0A=
> +++ b/arch/arm64/Kconfig=0A=
> @@ -187,6 +187,7 @@ config ARM64=0A=
>  	select HAVE_GCC_PLUGINS=0A=
>  	select HAVE_HW_BREAKPOINT if PERF_EVENTS=0A=
>  	select HAVE_IRQ_TIME_ACCOUNTING=0A=
> +	select HAVE_LIVEPATCH=0A=
>  	select HAVE_NMI=0A=
>  	select HAVE_PATA_PLATFORM=0A=
>  	select HAVE_PERF_EVENTS=0A=
> @@ -1946,3 +1947,5 @@ source "arch/arm64/kvm/Kconfig"=0A=
>  if CRYPTO=0A=
>  source "arch/arm64/crypto/Kconfig"=0A=
>  endif=0A=
> +=0A=
> +source "kernel/livepatch/Kconfig"=0A=
=0A=
I think ` source "kernel/livepatch/Kconfig"` should be placed between=0A=
`menu "Kernel Features"` and `endmenu`.=0A=
=0A=
=0A=
Thanks=0A=
Keiya=0A=
=0A=
=0A=
> diff --git a/arch/arm64/include/asm/livepatch.h b/arch/arm64/include/asm/=
livepatch.h=0A=
> new file mode 100644=0A=
> index 000000000000..72d7cd86f158=0A=
> --- /dev/null=0A=
> +++ b/arch/arm64/include/asm/livepatch.h=0A=
> @@ -0,0 +1,42 @@=0A=
> +/* SPDX-License-Identifier: GPL-2.0=0A=
> + *=0A=
> + * livepatch.h - arm64-specific Kernel Live Patching Core=0A=
> + */=0A=
> +#ifndef _ASM_ARM64_LIVEPATCH_H=0A=
> +#define _ASM_ARM64_LIVEPATCH_H=0A=
> +=0A=
> +#include <linux/ftrace.h>=0A=
> +=0A=
> +static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned l=
ong ip)=0A=
> +{=0A=
> +	struct pt_regs *regs =3D ftrace_get_regs(fregs);=0A=
> +=0A=
> +	regs->pc =3D ip;=0A=
> +}=0A=
> +=0A=
> +/*=0A=
> + * klp_get_ftrace_location is expected to return the address of the BL t=
o the=0A=
> + * relevant ftrace handler in the callsite. The location of this can var=
y based=0A=
> + * on several compilation options.=0A=
> + * CONFIG_DYNAMIC_FTRACE_WITH_REGS=0A=
> + *	- Inserts 2 nops on function entry the second of which is the BL=0A=
> + *	  referenced above. (See ftrace_init_nop() for the callsite sequence)=
=0A=
> + *	  (this is required by livepatch and must be selected)=0A=
> + * CONFIG_ARM64_BTI_KERNEL:=0A=
> + *	- Inserts a hint #0x22 on function entry if the function is called=0A=
> + *	  indirectly (to satisfy BTI requirements), which is inserted before=
=0A=
> + *	  the two nops from above.=0A=
> + */=0A=
> +#define klp_get_ftrace_location klp_get_ftrace_location=0A=
> +static inline unsigned long klp_get_ftrace_location(unsigned long faddr)=
=0A=
> +{=0A=
> +	unsigned long addr =3D faddr + AARCH64_INSN_SIZE;=0A=
> +=0A=
> +#if IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)=0A=
> +	addr =3D ftrace_location_range(addr, addr + AARCH64_INSN_SIZE);=0A=
> +#endif=0A=
> +=0A=
> +	return addr;=0A=
> +}=0A=
> +=0A=
> +#endif /* _ASM_ARM64_LIVEPATCH_H */=0A=
> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/as=
m/thread_info.h=0A=
> index 6623c99f0984..cca936d53a40 100644=0A=
> --- a/arch/arm64/include/asm/thread_info.h=0A=
> +++ b/arch/arm64/include/asm/thread_info.h=0A=
> @@ -67,6 +67,7 @@ int arch_dup_task_struct(struct task_struct *dst,=0A=
>  #define TIF_UPROBE		4	/* uprobe breakpoint or singlestep */=0A=
>  #define TIF_MTE_ASYNC_FAULT	5	/* MTE Asynchronous Tag Check Fault */=0A=
>  #define TIF_NOTIFY_SIGNAL	6	/* signal notifications exist */=0A=
> +#define TIF_PATCH_PENDING	7	/* pending live patching update */=0A=
>  #define TIF_SYSCALL_TRACE	8	/* syscall trace active */=0A=
>  #define TIF_SYSCALL_AUDIT	9	/* syscall auditing */=0A=
>  #define TIF_SYSCALL_TRACEPOINT	10	/* syscall tracepoint for ftrace */=0A=
> @@ -97,11 +98,12 @@ int arch_dup_task_struct(struct task_struct *dst,=0A=
>  #define _TIF_SVE		(1 << TIF_SVE)=0A=
>  #define _TIF_MTE_ASYNC_FAULT	(1 << TIF_MTE_ASYNC_FAULT)=0A=
>  #define _TIF_NOTIFY_SIGNAL	(1 << TIF_NOTIFY_SIGNAL)=0A=
> +#define _TIF_PATCH_PENDING	(1 << TIF_PATCH_PENDING)=0A=
> =0A=
>  #define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_SIGPENDING | \=0A=
>  				 _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \=0A=
>  				 _TIF_UPROBE | _TIF_MTE_ASYNC_FAULT | \=0A=
> -				 _TIF_NOTIFY_SIGNAL)=0A=
> +				 _TIF_NOTIFY_SIGNAL | _TIF_PATCH_PENDING)=0A=
> =0A=
>  #define _TIF_SYSCALL_WORK	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \=
=0A=
>  				 _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \=0A=
> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c=0A=
> index 6237486ff6bb..d1eedb0589a7 100644=0A=
> --- a/arch/arm64/kernel/signal.c=0A=
> +++ b/arch/arm64/kernel/signal.c=0A=
> @@ -18,6 +18,7 @@=0A=
>  #include <linux/sizes.h>=0A=
>  #include <linux/string.h>=0A=
>  #include <linux/tracehook.h>=0A=
> +#include <linux/livepatch.h>=0A=
>  #include <linux/ratelimit.h>=0A=
>  #include <linux/syscalls.h>=0A=
> =0A=
> @@ -932,6 +933,9 @@ asmlinkage void do_notify_resume(struct pt_regs *regs=
,=0A=
>  					       (void __user *)NULL, current);=0A=
>  			}=0A=
> =0A=
> +			if (thread_flags & _TIF_PATCH_PENDING)=0A=
> +				klp_update_patch_state(current);=0A=
> +=0A=
>  			if (thread_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))=0A=
>  				do_signal(regs);=0A=
> =0A=
> --=0A=
> 2.17.1=0A=
=0A=