[PATCH 1/8] riscv/kprobe: Prepare the skeleton to implement RISCV OPTPROBES feature
Conor Dooley
conor at kernel.org
Mon Oct 31 12:42:09 PDT 2022
Hey Chen Guokai,
On Sun, Oct 30, 2022 at 05:01:34PM +0800, Chen Guokai wrote:
> From: Liao Chang <liaochang1 at huawei.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 at mails.ucas.ac.cn>
> Signed-off-by: Chen Guokai <chenguokai17 at mails.ucas.ac.cn>
> Signed-off-by: Liao Chang <liaochang1 at huawei.com>
FYI, your signoff should come last since you're sending the patches, so
this would become:
> Signed-off-by: Liao Chang <liaochang1 at huawei.com>
> Co-developed-by: Chen Guokai <chenguokai17 at mails.ucas.ac.cn>
> Signed-off-by: Chen Guokai <chenguokai17 at mails.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 at mails.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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