[PATCH v6 3.2-rc1 27/28] uprobes: x86: introduce xol_was_trapped()

[Srikar Dronamraju]

Postpone the signals until we execute the probed insn. This is
simply wrong if xol insn traps and generates the signal itself. Say,
SIGILL/SIGSEGV/etc.

Adds xol_was_trapped() to detect this case. It assumes that anything
like do_page_fault/do_trap/etc sets thread.trap_no != -1.

We add uprobe_task_arch_info->saved_trap_no and change
pre_xol/post_xol to save/restore thread.trap_no, xol_was_trapped()
simply checks that ->trap_no is not equal to UPROBE_TRAP_NO == -1
set by pre_xol().

Original-patch-from: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/uprobes.h |    6 +++++-
 arch/x86/kernel/uprobes.c      |   21 +++++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
index 99d7d4b..78e0007 100644
--- a/arch/x86/include/asm/uprobes.h
+++ b/arch/x86/include/asm/uprobes.h
@@ -39,16 +39,20 @@ struct uprobe_arch_info {
 
 struct uprobe_task_arch_info {
 	unsigned long saved_scratch_register;
+	unsigned long saved_trap_no;
 };
 #else
 struct uprobe_arch_info {};
-struct uprobe_task_arch_info {};
+struct uprobe_task_arch_info {
+	unsigned long saved_trap_no;
+};
 #endif
 struct uprobe;
 extern int analyze_insn(struct mm_struct *mm, struct uprobe *uprobe);
 extern void set_instruction_pointer(struct pt_regs *regs, unsigned long vaddr);
 extern int pre_xol(struct uprobe *uprobe, struct pt_regs *regs);
 extern int post_xol(struct uprobe *uprobe, struct pt_regs *regs);
+extern bool xol_was_trapped(struct task_struct *tsk);
 extern int uprobe_exception_notify(struct notifier_block *self,
 				       unsigned long val, void *data);
 #endif	/* _ASM_UPROBES_H */
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 0792fc8..f5b0841 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -409,6 +409,8 @@ void set_instruction_pointer(struct pt_regs *regs, unsigned long vaddr)
 	regs->ip = vaddr;
 }
 
+#define	UPROBE_TRAP_NO	-1ul
+
 /*
  * pre_xol - prepare to execute out of line.
  * @uprobe: the probepoint information.
@@ -424,6 +426,9 @@ int pre_xol(struct uprobe *uprobe, struct pt_regs *regs)
 {
 	struct uprobe_task_arch_info *tskinfo = &current->utask->tskinfo;
 
+	tskinfo->saved_trap_no = current->thread.trap_no;
+	current->thread.trap_no = UPROBE_TRAP_NO;
+
 	regs->ip = current->utask->xol_vaddr;
 	if (uprobe->fixups & UPROBES_FIX_RIP_AX) {
 		tskinfo->saved_scratch_register = regs->ax;
@@ -439,6 +444,11 @@ int pre_xol(struct uprobe *uprobe, struct pt_regs *regs)
 #else
 int pre_xol(struct uprobe *uprobe, struct pt_regs *regs)
 {
+	struct uprobe_task_arch_info *tskinfo = &current->utask->tskinfo;
+
+	tskinfo->saved_trap_no = current->thread.trap_no;
+	current->thread.trap_no = UPROBE_TRAP_NO;
+
 	regs->ip = current->utask->xol_vaddr;
 	return 0;
 }
@@ -504,6 +514,14 @@ static void handle_riprel_post_xol(struct uprobe *uprobe,
 }
 #endif
 
+bool xol_was_trapped(struct task_struct *tsk)
+{
+	if (tsk->thread.trap_no != UPROBE_TRAP_NO)
+		return true;
+
+	return false;
+}
+
 /*
  * Called after single-stepping. To avoid the SMP problems that can
  * occur when we temporarily put back the original opcode to
@@ -534,6 +552,9 @@ int post_xol(struct uprobe *uprobe, struct pt_regs *regs)
 	int result = 0;
 	long correction;
 
+	WARN_ON_ONCE(current->thread.trap_no != UPROBE_TRAP_NO);
+
+	current->thread.trap_no = utask->tskinfo.saved_trap_no;
 	correction = (long)(utask->vaddr - utask->xol_vaddr);
 	handle_riprel_post_xol(uprobe, regs, &correction);
 	if (uprobe->fixups & UPROBES_FIX_IP)

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