[PATCH v2 5/8] arm64: kprobes: Avoid calling kprobes debug handlers explicitly

From: Will Deacon <will.deacon@arm•com>
To: linux-arm-kernel@lists•infradead.org
Cc: mark.rutland@arm•com, Will Deacon <will.deacon@arm•com>
Subject: [PATCH v2 5/8] arm64: kprobes: Avoid calling kprobes debug handlers explicitly
Date: Fri,  5 Apr 2019 13:40:45 +0100	[thread overview]
Message-ID: <20190405124048.3287-6-will.deacon@arm.com> (raw)
In-Reply-To: <20190405124048.3287-1-will.deacon@arm.com>

Kprobes bypasses our debug hook registration code so that it doesn't
get tangled up with recursive debug exceptions from things like lockdep:

  http://lists.infradead.org/pipermail/linux-arm-kernel/2015-February/324385.html

However, since then, (a) the hook list has become RCU protected and (b)
the kprobes hooks were found not to filter out exceptions from userspace
correctly. On top of that, the step handler is invoked directly from
single_step_handler(), which *does* use the debug hook list, so it's
clearly not the end of the world.

For now, have kprobes use the debug hook registration API like everybody
else. We can revisit this in the future if this is found to limit
coverage significantly.

Reviewed-by: Mark Rutland <mark.rutland@arm•com>
Signed-off-by: Will Deacon <will.deacon@arm•com>
---
 arch/arm64/include/asm/kprobes.h   |  2 --
 arch/arm64/kernel/debug-monitors.c | 10 ----------
 arch/arm64/kernel/probes/kprobes.c | 16 ++++++++++++++--
 3 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
index d5a44cf859e9..21721fbf44e7 100644
--- a/arch/arm64/include/asm/kprobes.h
+++ b/arch/arm64/include/asm/kprobes.h
@@ -54,8 +54,6 @@ void arch_remove_kprobe(struct kprobe *);
 int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
 int kprobe_exceptions_notify(struct notifier_block *self,
 			     unsigned long val, void *data);
-int kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr);
-int kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr);
 void kretprobe_trampoline(void);
 void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
 
diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
index 9b3fd7fa5b43..f4d8cda8830d 100644
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -258,10 +258,6 @@ static int single_step_handler(unsigned long unused, unsigned int esr,
 	if (!reinstall_suspended_bps(regs))
 		return 0;
 
-#ifdef	CONFIG_KPROBES
-	if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
-		handler_found = true;
-#endif
 	if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 		handler_found = true;
 
@@ -337,12 +333,6 @@ static int brk_handler(unsigned long unused, unsigned int esr,
 {
 	bool handler_found = false;
 
-#ifdef	CONFIG_KPROBES
-	if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
-		if (kprobe_breakpoint_handler(regs, esr) == DBG_HOOK_HANDLED)
-			handler_found = true;
-	}
-#endif
 	if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
 		handler_found = true;
 
diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index 7a679caf4585..baf97f47aec0 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -439,7 +439,7 @@ kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
 	return DBG_HOOK_ERROR;
 }
 
-int __kprobes
+static int __kprobes
 kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
 {
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
@@ -461,7 +461,11 @@ kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
 	return retval;
 }
 
-int __kprobes
+static struct step_hook kprobes_step_hook = {
+	.fn = kprobe_single_step_handler,
+};
+
+static int __kprobes
 kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
 {
 	if (user_mode(regs))
@@ -471,6 +475,11 @@ kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
 	return DBG_HOOK_HANDLED;
 }
 
+static struct break_hook kprobes_break_hook = {
+	.imm = BRK64_ESR_KPROBES,
+	.fn = kprobe_breakpoint_handler,
+};
+
 /*
  * Provide a blacklist of symbols identifying ranges which cannot be kprobed.
  * This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
@@ -599,5 +608,8 @@ int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 
 int __init arch_init_kprobes(void)
 {
+	register_kernel_break_hook(&kprobes_break_hook);
+	register_kernel_step_hook(&kprobes_step_hook);
+
 	return 0;
 }
-- 
2.11.0


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists•infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
