2 files changed, 35 insertions, 0 deletions

diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
index f3971bbcd1de..cee58624cb30 100644
--- a/arch/x86/include/asm/uprobes.h
+++ b/arch/x86/include/asm/uprobes.h
@@ -46,6 +46,8 @@ struct arch_uprobe_task {
 #ifdef CONFIG_X86_64
         unsigned long                   saved_scratch_register;
 #endif
+#define UPROBE_CLEAR_TF                 (1 << 0)
+        unsigned int                    restore_flags;
 };
 
 extern int  arch_uprobe_analyze_insn(struct arch_uprobe *aup, struct mm_struct *mm, unsigned long addr);
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 36fd42091fa7..309a0e02b124 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -41,6 +41,9 @@
 /* Adjust the return address of a call insn */
 #define UPROBE_FIX_CALL 0x2
 
+/* Instruction will modify TF, don't change it */
+#define UPROBE_FIX_SETF 0x4
+
 #define UPROBE_FIX_RIP_AX       0x8000
 #define UPROBE_FIX_RIP_CX       0x4000
 
@@ -239,6 +242,10 @@ static void prepare_fixups(struct arch_uprobe *auprobe, struct insn *insn)
         insn_get_opcode(insn);  /* should be a nop */
 
         switch (OPCODE1(insn)) {
+        case 0x9d:
+                /* popf */
+                auprobe->fixups |= UPROBE_FIX_SETF;
+                break;
         case 0xc3:              /* ret/lret */
         case 0xcb:
         case 0xc2:
@@ -673,3 +680,29 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
         }
         return false;
 }
+
+void arch_uprobe_enable_step(struct arch_uprobe *auprobe)
+{
+        struct uprobe_task      *utask          = current->utask;
+        struct arch_uprobe_task *autask         = &utask->autask;
+
+        autask->restore_flags = 0;
+        if (!test_tsk_thread_flag(current, TIF_SINGLESTEP) &&
+                        !(auprobe->fixups & UPROBE_FIX_SETF))
+                autask->restore_flags |= UPROBE_CLEAR_TF;
+        /*
+         * The state of TIF_BLOCKSTEP is not saved. With the TF flag set we
+         * would to examine the opcode and the flags to make it right. Without
+         * TF block stepping makes no sense.
+         */
+        user_enable_single_step(current);
+}
+
+void arch_uprobe_disable_step(struct arch_uprobe *auprobe)
+{
+        struct uprobe_task *utask               = current->utask;
+        struct arch_uprobe_task *autask         = &utask->autask;
+
+        if (autask->restore_flags & UPROBE_CLEAR_TF)
+                user_disable_single_step(current);
+}