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Message-Id: <20221030090141.2550837-2-chenguokai17@mails.ucas.ac.cn>
Date: Sun, 30 Oct 2022 17:01:34 +0800
From: Chen Guokai <chenguokai17@...ls.ucas.ac.cn>
To: paul.walmsley@...ive.com, palmer@...belt.com,
aou@...s.berkeley.edu, rostedt@...dmis.org, mingo@...hat.com,
sfr@...b.auug.org.au
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
liaochang1@...wei.com, Chen Guokai <chenguokai17@...ls.ucas.ac.cn>
Subject: [PATCH 1/8] riscv/kprobe: Prepare the skeleton to implement RISCV OPTPROBES feature
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.
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>
---
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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