uprobes/core: Handle breakpoint and singlestep exceptions

Uprobes uses exception notifiers to get to know if a thread hit
a breakpoint or a singlestep exception.

When a thread hits a uprobe or is singlestepping post a uprobe
hit, the uprobe exception notifier sets its TIF_UPROBE bit,
which will then be checked on its return to userspace path
(do_notify_resume() ->uprobe_notify_resume()), where the
consumers handlers are run (in task context) based on the
defined filters.

Uprobe hits are thread specific and hence we need to maintain
information about if a task hit a uprobe, what uprobe was hit,
the slot where the original instruction was copied for xol so
that it can be singlestepped with appropriate fixups.

In some cases, special care is needed for instructions that are
executed out of line (xol). These are architecture specific
artefacts, such as handling RIP relative instructions on x86_64.

Since the instruction at which the uprobe was inserted is
executed out of line, architecture specific fixups are added so
that the thread continues normal execution in the presence of a
uprobe.

Postpone the signals until we execute the probed insn.
post_xol() path does a recalc_sigpending() before return to
user-mode, this ensures the signal can't be lost.

Uprobes relies on DIE_DEBUG notification to notify if a
singlestep is complete.

Adds x86 specific uprobe exception notifiers and appropriate
hooks needed to determine a uprobe hit and subsequent post
processing.

Add requisite x86 fixups for xol for uprobes. Specific cases
needing fixups include relative jumps (x86_64), calls, etc.

Where possible, we check and skip singlestepping the
breakpointed instructions. For now we skip single byte as well
as few multibyte nop instructions. However this can be extended
to other instructions too.

Credits to Oleg Nesterov for suggestions/patches related to
signal, breakpoint, singlestep handling code.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@linux.vnet.ibm.com>
Cc: Linux-mm <linux-mm@kvack.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120313180011.29771.89027.sendpatchset@srdronam.in.ibm.com
[ Performed various cleanliness edits ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 56 insertions, 3 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7d379a6bfd88..8379e3771690 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1590,6 +1590,10 @@ struct task_struct {
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
 	atomic_t ptrace_bp_refcnt;
 #endif
+#ifdef CONFIG_UPROBES
+	struct uprobe_task *utask;
+	int uprobe_srcu_id;
+#endif
 };
 
 /* Future-safe accessor for struct task_struct's cpus_allowed. */
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index eac525f41b94..5ec778fdce6f 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -28,8 +28,9 @@
 #include <linux/rbtree.h>
 
 struct vm_area_struct;
+
 #ifdef CONFIG_ARCH_SUPPORTS_UPROBES
-#include <asm/uprobes.h>
+# include <asm/uprobes.h>
 #endif
 
 /* flags that denote/change uprobes behaviour */
@@ -39,6 +40,8 @@ struct vm_area_struct;
 
 /* Dont run handlers when first register/ last unregister in progress*/
 #define UPROBE_RUN_HANDLER	0x2
+/* Can skip singlestep */
+#define UPROBE_SKIP_SSTEP	0x4
 
 struct uprobe_consumer {
 	int (*handler)(struct uprobe_consumer *self, struct pt_regs *regs);
@@ -52,13 +55,42 @@ struct uprobe_consumer {
 };
 
 #ifdef CONFIG_UPROBES
+enum uprobe_task_state {
+	UTASK_RUNNING,
+	UTASK_BP_HIT,
+	UTASK_SSTEP,
+	UTASK_SSTEP_ACK,
+	UTASK_SSTEP_TRAPPED,
+};
+
+/*
+ * uprobe_task: Metadata of a task while it singlesteps.
+ */
+struct uprobe_task {
+	enum uprobe_task_state		state;
+	struct arch_uprobe_task		autask;
+
+	struct uprobe			*active_uprobe;
+
+	unsigned long			xol_vaddr;
+	unsigned long			vaddr;
+};
+
 extern int __weak set_swbp(struct arch_uprobe *aup, struct mm_struct *mm, unsigned long vaddr);
 extern int __weak set_orig_insn(struct arch_uprobe *aup, struct mm_struct *mm,  unsigned long vaddr, bool verify);
 extern bool __weak is_swbp_insn(uprobe_opcode_t *insn);
 extern int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *uc);
 extern void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc);
 extern int uprobe_mmap(struct vm_area_struct *vma);
-#else /* CONFIG_UPROBES is not defined */
+extern void uprobe_free_utask(struct task_struct *t);
+extern void uprobe_copy_process(struct task_struct *t);
+extern unsigned long __weak uprobe_get_swbp_addr(struct pt_regs *regs);
+extern int uprobe_post_sstep_notifier(struct pt_regs *regs);
+extern int uprobe_pre_sstep_notifier(struct pt_regs *regs);
+extern void uprobe_notify_resume(struct pt_regs *regs);
+extern bool uprobe_deny_signal(void);
+extern bool __weak arch_uprobe_skip_sstep(struct arch_uprobe *aup, struct pt_regs *regs);
+#else /* !CONFIG_UPROBES */
 static inline int
 uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *uc)
 {
@@ -72,5 +104,22 @@ static inline int uprobe_mmap(struct vm_area_struct *vma)
 {
 	return 0;
 }
-#endif /* CONFIG_UPROBES */
+static inline void uprobe_notify_resume(struct pt_regs *regs)
+{
+}
+static inline bool uprobe_deny_signal(void)
+{
+	return false;
+}
+static inline unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
+{
+	return 0;
+}
+static inline void uprobe_free_utask(struct task_struct *t)
+{
+}
+static inline void uprobe_copy_process(struct task_struct *t)
+{
+}
+#endif /* !CONFIG_UPROBES */
 #endif	/* _LINUX_UPROBES_H */