Re: [RFC PATCH v2 19/20] arm64: Miscellaneous changes required for enabling livepatch

[Miroslav Benes <mbenes@suse.cz>]

Hi,

sorry for the late reply...

On Mon, 23 May 2022, madvenka@linux.microsoft.com wrote:

> From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
> 
> 	- Create arch/arm64/include/asm/livepatch.h and define
> 	  klp_arch_set_pc() and klp_get_ftrace_location() which
> 	  are required for livepatch.
> 
> 	- Define TIF_PATCH_PENDING in arch/arm64/include/asm/thread_info.h
> 	  for livepatch.
> 
> 	- Check TIF_PATCH_PENDING in do_notify_resume() to patch the
> 	  current task for livepatch.
> 
> Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
> Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
> ---
>  arch/arm64/include/asm/livepatch.h   | 42 ++++++++++++++++++++++++++++
>  arch/arm64/include/asm/thread_info.h |  4 ++-
>  arch/arm64/kernel/signal.c           |  4 +++
>  3 files changed, 49 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/include/asm/livepatch.h
> 
> diff --git a/arch/arm64/include/asm/livepatch.h b/arch/arm64/include/asm/livepatch.h
> new file mode 100644
> index 000000000000..72d7cd86f158
> --- /dev/null
> +++ b/arch/arm64/include/asm/livepatch.h
> @@ -0,0 +1,42 @@
> +/* SPDX-License-Identifier: GPL-2.0
> + *
> + * livepatch.h - arm64-specific Kernel Live Patching Core
> + */
> +#ifndef _ASM_ARM64_LIVEPATCH_H
> +#define _ASM_ARM64_LIVEPATCH_H
> +
> +#include <linux/ftrace.h>
> +
> +static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
> +{
> +	struct pt_regs *regs = ftrace_get_regs(fregs);
> +
> +	regs->pc = ip;
> +}

kernel/livepatch/ does not use klp_arch_set_pc() anymore. It was replaced 
by ftrace_instruction_pointer_set() and 
CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS.

> +/*
> + * klp_get_ftrace_location is expected to return the address of the BL to the
> + * relevant ftrace handler in the callsite. The location of this can vary based
> + * on several compilation options.
> + * CONFIG_DYNAMIC_FTRACE_WITH_REGS
> + *	- Inserts 2 nops on function entry the second of which is the BL
> + *	  referenced above. (See ftrace_init_nop() for the callsite sequence)
> + *	  (this is required by livepatch and must be selected)
> + * CONFIG_ARM64_BTI_KERNEL:
> + *	- Inserts a hint #0x22 on function entry if the function is called
> + *	  indirectly (to satisfy BTI requirements), which is inserted before
> + *	  the two nops from above.
> + */
> +#define klp_get_ftrace_location klp_get_ftrace_location
> +static inline unsigned long klp_get_ftrace_location(unsigned long faddr)
> +{
> +	unsigned long addr = faddr + AARCH64_INSN_SIZE;
> +
> +#if IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)
> +	addr = ftrace_location_range(addr, addr + AARCH64_INSN_SIZE);
> +#endif
> +
> +	return addr;
> +}

This is not needed either. peterz improved the ftrace code and livepatch 
now uses ftrace_location() which gives the proper location directly.

> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
> index e1317b7c4525..a1d8999dbdcc 100644
> --- a/arch/arm64/include/asm/thread_info.h
> +++ b/arch/arm64/include/asm/thread_info.h
> @@ -68,6 +68,7 @@ int arch_dup_task_struct(struct task_struct *dst,
>  #define TIF_UPROBE		4	/* uprobe breakpoint or singlestep */
>  #define TIF_MTE_ASYNC_FAULT	5	/* MTE Asynchronous Tag Check Fault */
>  #define TIF_NOTIFY_SIGNAL	6	/* signal notifications exist */
> +#define TIF_PATCH_PENDING	7	/* pending live patching update */
>  #define TIF_SYSCALL_TRACE	8	/* syscall trace active */
>  #define TIF_SYSCALL_AUDIT	9	/* syscall auditing */
>  #define TIF_SYSCALL_TRACEPOINT	10	/* syscall tracepoint for ftrace */
> @@ -98,11 +99,12 @@ int arch_dup_task_struct(struct task_struct *dst,
>  #define _TIF_SVE		(1 << TIF_SVE)
>  #define _TIF_MTE_ASYNC_FAULT	(1 << TIF_MTE_ASYNC_FAULT)
>  #define _TIF_NOTIFY_SIGNAL	(1 << TIF_NOTIFY_SIGNAL)
> +#define _TIF_PATCH_PENDING	(1 << TIF_PATCH_PENDING)
>  
>  #define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
>  				 _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
>  				 _TIF_UPROBE | _TIF_MTE_ASYNC_FAULT | \
> -				 _TIF_NOTIFY_SIGNAL)
> +				 _TIF_NOTIFY_SIGNAL | _TIF_PATCH_PENDING)
>  
>  #define _TIF_SYSCALL_WORK	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
>  				 _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
> index 4a4122ef6f39..cbec9597349f 100644
> --- a/arch/arm64/kernel/signal.c
> +++ b/arch/arm64/kernel/signal.c
> @@ -17,6 +17,7 @@
>  #include <linux/sizes.h>
>  #include <linux/string.h>
>  #include <linux/resume_user_mode.h>
> +#include <linux/livepatch.h>
>  #include <linux/ratelimit.h>
>  #include <linux/syscalls.h>
>  
> @@ -938,6 +939,9 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_flags)
>  					       (void __user *)NULL, current);
>  			}
>  
> +			if (thread_flags & _TIF_PATCH_PENDING)
> +				klp_update_patch_state(current);
> +
>  			if (thread_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
>  				do_signal(regs);

The rest should be fine.

Regards

Miroslav