ARM kprobes: special hook for the kprobes breakpoint handler

Nicolas Pitre · Russell King · commit 796969104cab · 2008-01-26T15:25:17.000Z
The kprobes code is already able to cope with reentrant probes, so its
handler must be called outside of the region protected by undef_lock.

If ever this lock is released when handlers are called then this commit
could be reverted.

Signed-off-by: Nicolas Pitre &lt;nico@marvell.com&gt;
diff --git a/arch/arm/kernel/kprobes.c b/arch/arm/kernel/kprobes.c
@@ -26,12 +26,6 @@
 #include <asm/traps.h>
 #include <asm/cacheflush.h>
 
-/*
- * This undefined instruction must be unique and
- * reserved solely for kprobes' use.
- */
-#define KPROBE_BREAKPOINT_INSTRUCTION	0xe7f001f8
-
 #define MIN_STACK_SIZE(addr) 				\
 	min((unsigned long)MAX_STACK_SIZE,		\
 	    (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
@@ -206,7 +200,7 @@ void __kprobes kprobe_handler(struct pt_regs *regs)
 	}
 }
 
-static int kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
+int kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
 {
 	kprobe_handler(regs);
 	return 0;
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
@@ -19,6 +19,7 @@
 #include <linux/kallsyms.h>
 #include <linux/delay.h>
 #include <linux/init.h>
+#include <linux/kprobes.h>
 
 #include <asm/atomic.h>
 #include <asm/cacheflush.h>
@@ -313,6 +314,17 @@ asmlinkage void __exception do_undefinstr(struct pt_regs *regs)
 		get_user(instr, (u32 __user *)pc);
 	}
 
+#ifdef CONFIG_KPROBES
+	/*
+	 * It is possible to have recursive kprobes, so we can't call
+	 * the kprobe trap handler with the undef_lock held.
+	 */
+	if (instr == KPROBE_BREAKPOINT_INSTRUCTION && !user_mode(regs)) {
+		kprobe_trap_handler(regs, instr);
+		return;
+	}
+#endif
+
 	spin_lock_irqsave(&undef_lock, flags);
 	list_for_each_entry(hook, &undef_hook, node) {
 		if ((instr & hook->instr_mask) == hook->instr_val &&
diff --git a/include/asm-arm/kprobes.h b/include/asm-arm/kprobes.h
@@ -25,6 +25,12 @@
 #define MAX_INSN_SIZE			2
 #define MAX_STACK_SIZE			64	/* 32 would probably be OK */
 
+/*
+ * This undefined instruction must be unique and
+ * reserved solely for kprobes' use.
+ */
+#define KPROBE_BREAKPOINT_INSTRUCTION	0xe7f001f8
+
 #define regs_return_value(regs)		((regs)->ARM_r0)
 #define flush_insn_slot(p)		do { } while (0)
 #define kretprobe_blacklist_size	0
@@ -55,6 +61,7 @@ struct kprobe_ctlblk {
 
 void arch_remove_kprobe(struct kprobe *);
 
+int kprobe_trap_handler(struct pt_regs *regs, unsigned int instr);
 int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
 int kprobe_exceptions_notify(struct notifier_block *self,
 			     unsigned long val, void *data);

Original file line number	Diff line number	Diff line change
`@@ -26,12 +26,6 @@`
`26`	`26`	`#include <asm/traps.h>`
`27`	`27`	`#include <asm/cacheflush.h>`
`28`	`28`
`29`		`-/*`
`30`		`- * This undefined instruction must be unique and`
`31`		`- * reserved solely for kprobes' use.`
`32`		`- */`
`33`		`-#define KPROBE_BREAKPOINT_INSTRUCTION 0xe7f001f8`
`34`		`-`
`35`	`29`	`#define MIN_STACK_SIZE(addr) \`
`36`	`30`	`min((unsigned long)MAX_STACK_SIZE, \`
`37`	`31`	`(unsigned long)current_thread_info() + THREAD_START_SP - (addr))`
`@@ -206,7 +200,7 @@ void __kprobes kprobe_handler(struct pt_regs *regs)`
`206`	`200`	`}`
`207`	`201`	`}`
`208`	`202`
`209`		`-static int kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)`
	`203`	`+int kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)`
`210`	`204`	`{`
`211`	`205`	`kprobe_handler(regs);`
`212`	`206`	`return 0;`