Date:   Mon, 31 Oct 2022 19:42:09 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Chen Guokai <chenguokai17@...ls.ucas.ac.cn>
Cc:     paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, rostedt@...dmis.org, mingo@...hat.com,
        sfr@...b.auug.org.au, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, liaochang1@...wei.com
Subject: Re: [PATCH 1/8] riscv/kprobe: Prepare the skeleton to implement
 RISCV OPTPROBES feature

Hey Chen Guokai,

On Sun, Oct 30, 2022 at 05:01:34PM +0800, Chen Guokai wrote:
> From: Liao Chang <liaochang1@...wei.com>
> 
> Prepare skeleton to implement optimized kprobe on RISCV, it consists
> of Makfile, Kconfig and some architecture specific files: kprobe.h and
> opt.c opt.c includes some macro, type definition and functions required
> by kprobe framework, opt_trampoline.S provides a piece of assembly code
> template used to construct the detour buffer as the target of long jump
> instruction(s) for each optimzed kprobe.
> 
> Since the jump range of PC-relative instruction JAL is +/-1M, that is
> too small to reach the detour buffer, hence the foudamental idea to
> address OPTPROBES on RISCV is to replace 'EBREAK' with 'AUIPC+JALR'. which
> means it needs to clobber one more instruction beside the kprobe
> instruction, furthermore, RISCV supports hybird RVI and RVC in single
> kernel binary, so in theory a pair of 'AUIPC/JALR' is about to clobber
> 10 bytes(3 RVC and 1 RVI, 2 bytes is padding for alignment) at worst
> case. The second hardsome problem is looking for one integer register as
> the destination of 'AUIPC/JALR' without any side-effect.
> 
> More solution details will be introduced in the coming commits.

nit: you can drop this reference to future commits.

> 
> Co-developed-by: Chen Guokai <chenguokai17@...ls.ucas.ac.cn>
> Signed-off-by: Chen Guokai <chenguokai17@...ls.ucas.ac.cn>
> Signed-off-by: Liao Chang <liaochang1@...wei.com>

FYI, your signoff should come last since you're sending the patches, so
this would become:

> Signed-off-by: Liao Chang <liaochang1@...wei.com>
> Co-developed-by: Chen Guokai <chenguokai17@...ls.ucas.ac.cn>
> Signed-off-by: Chen Guokai <chenguokai17@...ls.ucas.ac.cn>

I noticed on some of the other patches that your SoB is missing there,
for example patch 2.

Thanks,
Conor.

> ---
>  arch/riscv/Kconfig                        |  1 +
>  arch/riscv/include/asm/kprobes.h          | 32 ++++++++++++++
>  arch/riscv/kernel/probes/Makefile         |  1 +
>  arch/riscv/kernel/probes/opt.c            | 51 +++++++++++++++++++++++
>  arch/riscv/kernel/probes/opt_trampoline.S | 12 ++++++
>  5 files changed, 97 insertions(+)
>  create mode 100644 arch/riscv/kernel/probes/opt.c
>  create mode 100644 arch/riscv/kernel/probes/opt_trampoline.S
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 6b48a3ae9843..ca29306c93e2 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -99,6 +99,7 @@ config RISCV
>  	select HAVE_KPROBES if !XIP_KERNEL
>  	select HAVE_KPROBES_ON_FTRACE if !XIP_KERNEL
>  	select HAVE_KRETPROBES if !XIP_KERNEL
> +	select HAVE_OPTPROBES if !XIP_KERNEL
>  	select HAVE_MOVE_PMD
>  	select HAVE_MOVE_PUD
>  	select HAVE_PCI
> diff --git a/arch/riscv/include/asm/kprobes.h b/arch/riscv/include/asm/kprobes.h
> index 217ef89f22b9..22b73a2fd1fd 100644
> --- a/arch/riscv/include/asm/kprobes.h
> +++ b/arch/riscv/include/asm/kprobes.h
> @@ -43,5 +43,37 @@ bool kprobe_single_step_handler(struct pt_regs *regs);
>  void __kretprobe_trampoline(void);
>  void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
>  
> +#ifdef CONFIG_OPTPROBES
> +
> +/* optinsn template addresses */
> +extern __visible kprobe_opcode_t optprobe_template_entry[];
> +extern __visible kprobe_opcode_t optprobe_template_end[];
> +
> +#define MAX_OPTINSN_SIZE				\
> +	((unsigned long)optprobe_template_end -		\
> +	 (unsigned long)optprobe_template_entry)
> +
> +/*
> + * For RVI and RVC hybird encoding kernel, althought long jump just needs
> + * 2 RVI instructions(AUIPC+JALR), optimized instructions is 10 bytes long
> + * at most to ensure no RVI would be truncated actually, so it means four
> + * combinations:
> + * - 2 RVI
> + * - 4 RVC
> + * - 2 RVC + 1 RVI
> + * - 3 RVC + 1 RVI (truncated, need padding)
> + */
> +#define MAX_COPIED_INSN		4
> +#define MAX_OPTIMIZED_LENGTH	10
> +
> +struct arch_optimized_insn {
> +	kprobe_opcode_t copied_insn[MAX_COPIED_INSN];
> +	/* detour code buffer */
> +	kprobe_opcode_t *insn;
> +	unsigned long length;
> +	int rd;
> +};
> +
> +#endif /* CONFIG_OPTPROBES */
>  #endif /* CONFIG_KPROBES */
>  #endif /* _ASM_RISCV_KPROBES_H */
> diff --git a/arch/riscv/kernel/probes/Makefile b/arch/riscv/kernel/probes/Makefile
> index 7f0840dcc31b..6255b4600875 100644
> --- a/arch/riscv/kernel/probes/Makefile
> +++ b/arch/riscv/kernel/probes/Makefile
> @@ -3,4 +3,5 @@ obj-$(CONFIG_KPROBES)		+= kprobes.o decode-insn.o simulate-insn.o
>  obj-$(CONFIG_KPROBES)		+= kprobes_trampoline.o
>  obj-$(CONFIG_KPROBES_ON_FTRACE)	+= ftrace.o
>  obj-$(CONFIG_UPROBES)		+= uprobes.o decode-insn.o simulate-insn.o
> +obj-$(CONFIG_OPTPROBES)		+= opt.o opt_trampoline.o
>  CFLAGS_REMOVE_simulate-insn.o = $(CC_FLAGS_FTRACE)
> diff --git a/arch/riscv/kernel/probes/opt.c b/arch/riscv/kernel/probes/opt.c
> new file mode 100644
> index 000000000000..56c8a227c857
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/opt.c
> @@ -0,0 +1,51 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + *  Kernel Probes Jump Optimization (Optprobes)
> + *
> + * Copyright (C) Guokai Chen, 2022
> + * Author: Guokai Chen chenguokai17@...ls.ucas.ac.cn
> + */
> +
> +#define pr_fmt(fmt)	"optprobe: " fmt
> +
> +#include <linux/kprobes.h>
> +#include <asm/kprobes.h>
> +
> +int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
> +{
> +	return 0;
> +}
> +
> +int arch_check_optimized_kprobe(struct optimized_kprobe *op)
> +{
> +	return 0;
> +}
> +
> +int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
> +				  struct kprobe *orig)
> +{
> +	return 0;
> +}
> +
> +void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
> +{
> +}
> +
> +void arch_optimize_kprobes(struct list_head *oplist)
> +{
> +}
> +
> +void arch_unoptimize_kprobes(struct list_head *oplist,
> +			     struct list_head *done_list)
> +{
> +}
> +
> +void arch_unoptimize_kprobe(struct optimized_kprobe *op)
> +{
> +}
> +
> +int arch_within_optimized_kprobe(struct optimized_kprobe *op,
> +				 kprobe_opcode_t *addr)
> +{
> +	return 0;
> +}
> diff --git a/arch/riscv/kernel/probes/opt_trampoline.S b/arch/riscv/kernel/probes/opt_trampoline.S
> new file mode 100644
> index 000000000000..16160c4367ff
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/opt_trampoline.S
> @@ -0,0 +1,12 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2022 Guokai Chen
> + */
> +
> +#include <linux/linkage.h>
> +
> +#incldue <asm/csr.h>
> +#include <asm/asm-offsets.h>
> +
> +SYM_ENTRY(optprobe_template_entry, SYM_L_GLOBAL, SYM_A_NONE)
> +SYM_ENTRY(optprobe_template_end, SYM_L_GLOBAL, SYM_A_NONE)
> -- 
> 2.25.1
> 
> 
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