linux-kernel - [PATCH] riscv: kprobes: Remove redundant kprobe_step

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Message-ID: <20210419002919.1a0a539d@xhacker>
Date:   Mon, 19 Apr 2021 00:29:19 +0800
From:   Jisheng Zhang <jszhang3@...l.ustc.edu.cn>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] riscv: kprobes: Remove redundant kprobe_step_ctx

From: Jisheng Zhang <jszhang@...nel.org>

Inspired by commit ba090f9cafd5 ("arm64: kprobes: Remove redundant
kprobe_step_ctx"), the ss_pending and match_addr of kprobe_step_ctx
are redundant because those can be replaced by KPROBE_HIT_SS and
&cur_kprobe->ainsn.api.insn[0] + GET_INSN_LENGTH(cur->opcode)
respectively.

Remove the kprobe_step_ctx to simplify the code.

Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
---
 arch/riscv/include/asm/kprobes.h   |  7 ------
 arch/riscv/kernel/probes/kprobes.c | 40 +++++++-----------------------
 2 files changed, 9 insertions(+), 38 deletions(-)

diff --git a/arch/riscv/include/asm/kprobes.h b/arch/riscv/include/asm/kprobes.h
index 4647d38018f6..9ea9b5ec3113 100644
--- a/arch/riscv/include/asm/kprobes.h
+++ b/arch/riscv/include/asm/kprobes.h
@@ -29,18 +29,11 @@ struct prev_kprobe {
 	unsigned int status;
 };
 
-/* Single step context for kprobe */
-struct kprobe_step_ctx {
-	unsigned long ss_pending;
-	unsigned long match_addr;
-};
-
 /* per-cpu kprobe control block */
 struct kprobe_ctlblk {
 	unsigned int kprobe_status;
 	unsigned long saved_status;
 	struct prev_kprobe prev_kprobe;
-	struct kprobe_step_ctx ss_ctx;
 };
 
 void arch_remove_kprobe(struct kprobe *p);
diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
index 8c1f7a30aeed..4c1ad5536748 100644
--- a/arch/riscv/kernel/probes/kprobes.c
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -17,7 +17,7 @@ DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 
 static void __kprobes
-post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
+post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
 
 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 {
@@ -43,7 +43,7 @@ static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
 		p->ainsn.api.handler((u32)p->opcode,
 					(unsigned long)p->addr, regs);
 
-	post_kprobe_handler(kcb, regs);
+	post_kprobe_handler(p, kcb, regs);
 }
 
 int __kprobes arch_prepare_kprobe(struct kprobe *p)
@@ -149,21 +149,6 @@ static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
 	regs->status = kcb->saved_status;
 }
 
-static void __kprobes
-set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr, struct kprobe *p)
-{
-	unsigned long offset = GET_INSN_LENGTH(p->opcode);
-
-	kcb->ss_ctx.ss_pending = true;
-	kcb->ss_ctx.match_addr = addr + offset;
-}
-
-static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
-{
-	kcb->ss_ctx.ss_pending = false;
-	kcb->ss_ctx.match_addr = 0;
-}
-
 static void __kprobes setup_singlestep(struct kprobe *p,
 				       struct pt_regs *regs,
 				       struct kprobe_ctlblk *kcb, int reenter)
@@ -182,8 +167,6 @@ static void __kprobes setup_singlestep(struct kprobe *p,
 		/* prepare for single stepping */
 		slot = (unsigned long)p->ainsn.api.insn;
 
-		set_ss_context(kcb, slot, p);	/* mark pending ss */
-
 		/* IRQs and single stepping do not mix well. */
 		kprobes_save_local_irqflag(kcb, regs);
 
@@ -219,13 +202,8 @@ static int __kprobes reenter_kprobe(struct kprobe *p,
 }
 
 static void __kprobes
-post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
+post_kprobe_handler(struct kprobe *cur, struct kprobe_ctlblk *kcb, struct pt_regs *regs)
 {
-	struct kprobe *cur = kprobe_running();
-
-	if (!cur)
-		return;
-
 	/* return addr restore if non-branching insn */
 	if (cur->ainsn.api.restore != 0)
 		regs->epc = cur->ainsn.api.restore;
@@ -355,16 +333,16 @@ bool __kprobes
 kprobe_single_step_handler(struct pt_regs *regs)
 {
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	unsigned long addr = instruction_pointer(regs);
+	struct kprobe *cur = kprobe_running();
 
-	if ((kcb->ss_ctx.ss_pending)
-	    && (kcb->ss_ctx.match_addr == instruction_pointer(regs))) {
-		clear_ss_context(kcb);	/* clear pending ss */
-
+	if (cur && (kcb->kprobe_status & (KPROBE_HIT_SS | KPROBE_REENTER)) &&
+	    ((unsigned long)&cur->ainsn.api.insn[0] + GET_INSN_LENGTH(cur->opcode) == addr)) {
 		kprobes_restore_local_irqflag(kcb, regs);
-
-		post_kprobe_handler(kcb, regs);
+		post_kprobe_handler(cur, kcb, regs);
 		return true;
 	}
+	/* not ours, kprobes should ignore it */
 	return false;
 }
 
-- 
2.31.0