Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Anshuman Khandual <anshuman.khandual@arm.com>
To:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc:     akpm@linux-foundation.org, linux@roeck-us.net
Subject: [DRAFT] mm/kprobes: Add generic kprobe_fault_handler() fallback definition
Date:   Mon,  1 Jul 2019 15:05:57 +0530
Message-Id: <1561973757-5445-1-git-send-email-anshuman.khandual@arm.com>
In-Reply-To: <78863cd0-8cb5-c4fd-ed06-b1136bdbb6ef@arm.com>
References: <78863cd0-8cb5-c4fd-ed06-b1136bdbb6ef@arm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Architectures like parisc enable CONFIG_KROBES without having a definition
for kprobe_fault_handler() which results in a build failure. Arch needs to
provide kprobe_fault_handler() as it is platform specific and cannot have
a generic working alternative. But in the event when platform lacks such a
definition there needs to be a fallback.

This adds a stub kprobe_fault_handler() definition which not only prevents
a build failure but also makes sure that kprobe_page_fault() if called will
always return negative in absence of a sane platform specific alternative.

While here wrap kprobe_page_fault() in CONFIG_KPROBES. This enables stud
definitions for generic kporbe_fault_handler() and kprobes_built_in() can
just be dropped. Only on x86 it needs to be added back locally as it gets
used in a !CONFIG_KPROBES function do_general_protection().

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
I am planning to go with approach unless we just want to implement a stub
definition for parisc to get around the build problem for now.

Hello Guenter,

Could you please test this in your parisc setup. Thank you.

- Anshuman

 arch/arc/include/asm/kprobes.h     |  1 +
 arch/arm/include/asm/kprobes.h     |  1 +
 arch/arm64/include/asm/kprobes.h   |  1 +
 arch/ia64/include/asm/kprobes.h    |  1 +
 arch/mips/include/asm/kprobes.h    |  1 +
 arch/powerpc/include/asm/kprobes.h |  1 +
 arch/s390/include/asm/kprobes.h    |  1 +
 arch/sh/include/asm/kprobes.h      |  1 +
 arch/sparc/include/asm/kprobes.h   |  1 +
 arch/x86/include/asm/kprobes.h     |  6 ++++++
 include/linux/kprobes.h            | 32 ++++++++++++++++++------------
 11 files changed, 34 insertions(+), 13 deletions(-)

diff --git a/arch/arc/include/asm/kprobes.h b/arch/arc/include/asm/kprobes.h
index 2134721dce44..ee8efe256675 100644
--- a/arch/arc/include/asm/kprobes.h
+++ b/arch/arc/include/asm/kprobes.h
@@ -45,6 +45,7 @@ struct kprobe_ctlblk {
 	struct prev_kprobe prev_kprobe;
 };
 
+#define kprobe_fault_handler kprobe_fault_handler
 int kprobe_fault_handler(struct pt_regs *regs, unsigned long cause);
 void kretprobe_trampoline(void);
 void trap_is_kprobe(unsigned long address, struct pt_regs *regs);
diff --git a/arch/arm/include/asm/kprobes.h b/arch/arm/include/asm/kprobes.h
index 213607a1f45c..660f877b989f 100644
--- a/arch/arm/include/asm/kprobes.h
+++ b/arch/arm/include/asm/kprobes.h
@@ -38,6 +38,7 @@ struct kprobe_ctlblk {
 	struct prev_kprobe prev_kprobe;
 };
 
+#define kprobe_fault_handler kprobe_fault_handler
 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,
diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
index 97e511d645a2..667773f75616 100644
--- a/arch/arm64/include/asm/kprobes.h
+++ b/arch/arm64/include/asm/kprobes.h
@@ -42,6 +42,7 @@ struct kprobe_ctlblk {
 	struct kprobe_step_ctx ss_ctx;
 };
 
+#define kprobe_fault_handler kprobe_fault_handler
 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,
diff --git a/arch/ia64/include/asm/kprobes.h b/arch/ia64/include/asm/kprobes.h
index c5cf5e4fb338..c321e8585089 100644
--- a/arch/ia64/include/asm/kprobes.h
+++ b/arch/ia64/include/asm/kprobes.h
@@ -106,6 +106,7 @@ struct arch_specific_insn {
 	unsigned short slot;
 };
 
+#define kprobe_fault_handler kprobe_fault_handler
 extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
 extern int kprobe_exceptions_notify(struct notifier_block *self,
 				    unsigned long val, void *data);
diff --git a/arch/mips/include/asm/kprobes.h b/arch/mips/include/asm/kprobes.h
index 68b1e5d458cf..d1efe991ea22 100644
--- a/arch/mips/include/asm/kprobes.h
+++ b/arch/mips/include/asm/kprobes.h
@@ -40,6 +40,7 @@ do {									\
 
 #define kretprobe_blacklist_size 0
 
+#define kprobe_fault_handler kprobe_fault_handler
 void arch_remove_kprobe(struct kprobe *p);
 int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
 
diff --git a/arch/powerpc/include/asm/kprobes.h b/arch/powerpc/include/asm/kprobes.h
index 66b3f2983b22..c94f375ec957 100644
--- a/arch/powerpc/include/asm/kprobes.h
+++ b/arch/powerpc/include/asm/kprobes.h
@@ -84,6 +84,7 @@ struct arch_optimized_insn {
 	kprobe_opcode_t *insn;
 };
 
+#define kprobe_fault_handler kprobe_fault_handler
 extern int kprobe_exceptions_notify(struct notifier_block *self,
 					unsigned long val, void *data);
 extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
diff --git a/arch/s390/include/asm/kprobes.h b/arch/s390/include/asm/kprobes.h
index b106aa29bf55..0ecaebb78092 100644
--- a/arch/s390/include/asm/kprobes.h
+++ b/arch/s390/include/asm/kprobes.h
@@ -73,6 +73,7 @@ struct kprobe_ctlblk {
 void arch_remove_kprobe(struct kprobe *p);
 void kretprobe_trampoline(void);
 
+#define kprobe_fault_handler kprobe_fault_handler
 int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
 int kprobe_exceptions_notify(struct notifier_block *self,
 	unsigned long val, void *data);
diff --git a/arch/sh/include/asm/kprobes.h b/arch/sh/include/asm/kprobes.h
index 6171682f7798..637a698393c0 100644
--- a/arch/sh/include/asm/kprobes.h
+++ b/arch/sh/include/asm/kprobes.h
@@ -45,6 +45,7 @@ struct kprobe_ctlblk {
 	struct prev_kprobe prev_kprobe;
 };
 
+#define kprobe_fault_handler kprobe_fault_handler
 extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
 extern int kprobe_exceptions_notify(struct notifier_block *self,
 				    unsigned long val, void *data);
diff --git a/arch/sparc/include/asm/kprobes.h b/arch/sparc/include/asm/kprobes.h
index bfcaa6326c20..9aa4d25a45a8 100644
--- a/arch/sparc/include/asm/kprobes.h
+++ b/arch/sparc/include/asm/kprobes.h
@@ -47,6 +47,7 @@ struct kprobe_ctlblk {
 	struct prev_kprobe prev_kprobe;
 };
 
+#define kprobe_fault_handler kprobe_fault_handler
 int kprobe_exceptions_notify(struct notifier_block *self,
 			     unsigned long val, void *data);
 int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
diff --git a/arch/x86/include/asm/kprobes.h b/arch/x86/include/asm/kprobes.h
index 5dc909d9ad81..1af2b6db13bd 100644
--- a/arch/x86/include/asm/kprobes.h
+++ b/arch/x86/include/asm/kprobes.h
@@ -101,11 +101,17 @@ struct kprobe_ctlblk {
 	struct prev_kprobe prev_kprobe;
 };
 
+#define kprobe_fault_handler kprobe_fault_handler
 extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
 extern int kprobe_exceptions_notify(struct notifier_block *self,
 				    unsigned long val, void *data);
 extern int kprobe_int3_handler(struct pt_regs *regs);
 extern int kprobe_debug_handler(struct pt_regs *regs);
+#else
+static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
+{
+	return 0;
+}
 
 #endif /* CONFIG_KPROBES */
 #endif /* _ASM_X86_KPROBES_H */
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 04bdaf01112c..e106f3018804 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -182,11 +182,19 @@ DECLARE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 /*
  * For #ifdef avoidance:
  */
-static inline int kprobes_built_in(void)
+
+/*
+ * Architectures need to override this with their own implementation
+ * if they care to call kprobe_page_fault(). This will just ensure
+ * that kprobe_page_fault() returns false when called without having
+ * a proper platform specific definition for kprobe_fault_handler().
+ */
+#ifndef kprobe_fault_handler
+static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 {
-	return 1;
+	return 0;
 }
-
+#endif
 #ifdef CONFIG_KRETPROBES
 extern void arch_prepare_kretprobe(struct kretprobe_instance *ri,
 				   struct pt_regs *regs);
@@ -375,14 +383,6 @@ void free_insn_page(void *page);
 
 #else /* !CONFIG_KPROBES: */
 
-static inline int kprobes_built_in(void)
-{
-	return 0;
-}
-static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
-{
-	return 0;
-}
 static inline struct kprobe *get_kprobe(void *addr)
 {
 	return NULL;
@@ -458,12 +458,11 @@ static inline bool is_kprobe_optinsn_slot(unsigned long addr)
 }
 #endif
 
+#ifdef CONFIG_KPROBES
 /* Returns true if kprobes handled the fault */
 static nokprobe_inline bool kprobe_page_fault(struct pt_regs *regs,
 					      unsigned int trap)
 {
-	if (!kprobes_built_in())
-		return false;
 	if (user_mode(regs))
 		return false;
 	/*
@@ -476,5 +475,12 @@ static nokprobe_inline bool kprobe_page_fault(struct pt_regs *regs,
 		return false;
 	return kprobe_fault_handler(regs, trap);
 }
+#else
+static nokprobe_inline bool kprobe_page_fault(struct pt_regs *regs,
+					      unsigned int trap)
+{
+	return false;
+}
+#endif
 
 #endif /* _LINUX_KPROBES_H */
-- 
2.20.1