Re: [DRAFT] mm/kprobes: Add generic kprobe_fault_handler() fallback definition

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On 7/1/19 2:35 AM, Anshuman Khandual wrote:
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@xxxxxxx>
---
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.


With this patch applied on top of next-20190628, parisc:allmodconfig builds
correctly. I scheduled a full build for tonight for all architectures.

Guenter

- 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 */





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