[v2,2/2] arm64: kprobes: Remove redundant kprobe_step_ctx

Commit Message

Jean-Philippe Brucker Nov. 3, 2020, 1:49 p.m. UTC

From: Masami Hiramatsu <[e-mail]>

The kprobe_step_ctx (kcb->ss_ctx) has ss_pending and match_addr, but
those are redundant because those can be replaced by KPROBE_HIT_SS and
&cur_kprobe->ainsn.api.insn[1] respectively.
To simplify the code, remove the kprobe_step_ctx.

Reviewed-by: Jean-Philippe Brucker <[e-mail]>
Signed-off-by: Masami Hiramatsu <[e-mail]>
---
 arch/arm64/include/asm/kprobes.h   |  7 ----
 arch/arm64/kernel/probes/kprobes.c | 53 +++++++-----------------------
 2 files changed, 12 insertions(+), 48 deletions(-)

Comments

Will Deacon Nov. 3, 2020, 3:01 p.m. UTC | #1

On Tue, Nov 03, 2020 at 02:49:04PM +0100, Jean-Philippe Brucker wrote:
> From: Masami Hiramatsu <[e-mail]>
> 
> The kprobe_step_ctx (kcb->ss_ctx) has ss_pending and match_addr, but
> those are redundant because those can be replaced by KPROBE_HIT_SS and
> &cur_kprobe->ainsn.api.insn[1] respectively.
> To simplify the code, remove the kprobe_step_ctx.
> 
> Reviewed-by: Jean-Philippe Brucker <[e-mail]>
> Signed-off-by: Masami Hiramatsu <[e-mail]>
> ---
>  arch/arm64/include/asm/kprobes.h   |  7 ----
>  arch/arm64/kernel/probes/kprobes.c | 53 +++++++-----------------------
>  2 files changed, 12 insertions(+), 48 deletions(-)

Acked-by: Will Deacon <[e-mail]>

Catalin should be able to queue this at -rc3, once the first patch has
landed in mainline.

Cheers,

Will

Catalin Marinas Nov. 10, 2020, 7:24 p.m. UTC | #2

On Tue, Nov 03, 2020 at 03:01:52PM +0000, Will Deacon wrote:
> On Tue, Nov 03, 2020 at 02:49:04PM +0100, Jean-Philippe Brucker wrote:
> > From: Masami Hiramatsu <[e-mail]>
> > 
> > The kprobe_step_ctx (kcb->ss_ctx) has ss_pending and match_addr, but
> > those are redundant because those can be replaced by KPROBE_HIT_SS and
> > &cur_kprobe->ainsn.api.insn[1] respectively.
> > To simplify the code, remove the kprobe_step_ctx.
> > 
> > Reviewed-by: Jean-Philippe Brucker <[e-mail]>
> > Signed-off-by: Masami Hiramatsu <[e-mail]>
> > ---
> >  arch/arm64/include/asm/kprobes.h   |  7 ----
> >  arch/arm64/kernel/probes/kprobes.c | 53 +++++++-----------------------
> >  2 files changed, 12 insertions(+), 48 deletions(-)
> 
> Acked-by: Will Deacon <[e-mail]>
> 
> Catalin should be able to queue this at -rc3, once the first patch has
> landed in mainline.

I queued it but couldn't convince "b4 ty" to reply to patch 2:

https://git.kernel.org/arm64/c/ba090f9cafd53dbabe0f0a8c4ccae44203d3731b

Patch

diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
index 8699ce30f587..5d38ff4a4806 100644
--- a/arch/arm64/include/asm/kprobes.h
+++ b/arch/arm64/include/asm/kprobes.h
@@ -28,18 +28,11 @@  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_irqflag;
 	struct prev_kprobe prev_kprobe;
-	struct kprobe_step_ctx ss_ctx;
 };
 
 void arch_remove_kprobe(struct kprobe *);
diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index f11a1a1f7026..89c64ada8732 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -34,7 +34,7 @@  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)
 {
@@ -68,7 +68,7 @@  static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
 		p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);
 
 	/* single step simulated, now go for post processing */
-	post_kprobe_handler(kcb, regs);
+	post_kprobe_handler(p, kcb, regs);
 }
 
 int __kprobes arch_prepare_kprobe(struct kprobe *p)
@@ -177,19 +177,6 @@  static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
 	regs->pstate |= kcb->saved_irqflag;
 }
 
-static void __kprobes
-set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
-{
-	kcb->ss_ctx.ss_pending = true;
-	kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
-}
-
-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)
@@ -209,7 +196,6 @@  static void __kprobes setup_singlestep(struct kprobe *p,
 		/* prepare for single stepping */
 		slot = (unsigned long)p->ainsn.api.insn;
 
-		set_ss_context(kcb, slot);	/* mark pending ss */
 		kprobes_save_local_irqflag(kcb, regs);
 		instruction_pointer_set(regs, slot);
 	} else {
@@ -243,13 +229,8 @@  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)
 		instruction_pointer_set(regs, cur->ainsn.api.restore);
@@ -364,33 +345,23 @@  static void __kprobes kprobe_handler(struct pt_regs *regs)
 	 */
 }
 
-static int __kprobes
-kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
-{
-	if ((kcb->ss_ctx.ss_pending)
-	    && (kcb->ss_ctx.match_addr == addr)) {
-		clear_ss_context(kcb);	/* clear pending ss */
-		return DBG_HOOK_HANDLED;
-	}
-	/* not ours, kprobes should ignore it */
-	return DBG_HOOK_ERROR;
-}
-
 static int __kprobes
 kprobe_breakpoint_ss_handler(struct pt_regs *regs, unsigned int esr)
 {
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
-	int retval;
-
-	/* return error if this is not our step */
-	retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
+	unsigned long addr = instruction_pointer(regs);
+	struct kprobe *cur = kprobe_running();
 
-	if (retval == DBG_HOOK_HANDLED) {
+	if (cur && (kcb->kprobe_status == KPROBE_HIT_SS)
+	    && ((unsigned long)&cur->ainsn.api.insn[1] == addr)) {
 		kprobes_restore_local_irqflag(kcb, regs);
-		post_kprobe_handler(kcb, regs);
+		post_kprobe_handler(cur, kcb, regs);
+
+		return DBG_HOOK_HANDLED;
 	}
 
-	return retval;
+	/* not ours, kprobes should ignore it */
+	return DBG_HOOK_ERROR;
 }
 
 static struct break_hook kprobes_break_ss_hook = {