x86 ptrace: unify TIF_SINGLESTEP

This unifies the treatment of TIF_SINGLESTEP on i386 and x86_64.
The bit is now excluded from _TIF_WORK_MASK on i386 as it has been
on x86_64.  This means the do_notify_resume() path using it is never
used, so TIF_SINGLESTEP is not cleared on returning to user mode.

Both now leave TIF_SINGLESTEP set when returning to user, so that
it's already set on an int $0x80 system call entry.  This removes
the need for testing TF on the system_call path.  Doing it this way
fixes the regression for PTRACE_SINGLESTEP into a sigreturn syscall,
introduced by commit 1e2e99f0e4aa6363e8515ed17011c210c8f1b52a.

The clear_TF_reenable case that sets TIF_SINGLESTEP can only happen
on a non-exception kernel entry, i.e. sysenter/syscall instruction.
That will always get to the syscall exit tracing path.

Signed-off-by: Roland McGrath <roland@redhat.com>

4 files changed, 2 insertions, 18 deletions

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 6bc07f0f1202..0ad987d02b72 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -383,10 +383,6 @@ syscall_exit:
                                         # setting need_resched or sigpending
                                         # between sampling and the iret
         TRACE_IRQS_OFF
-        testl $X86_EFLAGS_TF,PT_EFLAGS(%esp)    # If tracing set singlestep flag on exit
-        jz no_singlestep
-        orl $_TIF_SINGLESTEP,TI_flags(%ebp)
-no_singlestep:
         movl TI_flags(%ebp), %ecx
         testw $_TIF_ALLWORK_MASK, %cx   # current->work
         jne syscall_exit_work
diff --git a/arch/x86/kernel/signal_32.c b/arch/x86/kernel/signal_32.c
index d92373630963..295b5f5c9389 100644
--- a/arch/x86/kernel/signal_32.c
+++ b/arch/x86/kernel/signal_32.c
@@ -657,12 +657,6 @@ static void do_signal(struct pt_regs *regs)
 void
 do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
 {
-        /* Pending single-step? */
-        if (thread_info_flags & _TIF_SINGLESTEP) {
-                regs->flags |= X86_EFLAGS_TF;
-                clear_thread_flag(TIF_SINGLESTEP);
-        }
-
         /* deal with pending signal delivery */
         if (thread_info_flags & _TIF_SIGPENDING)
                 do_signal(regs);
diff --git a/arch/x86/kernel/signal_64.c b/arch/x86/kernel/signal_64.c
index e53b267662e7..bf87684474f1 100644
--- a/arch/x86/kernel/signal_64.c
+++ b/arch/x86/kernel/signal_64.c
@@ -487,12 +487,6 @@ static void do_signal(struct pt_regs *regs)
 void do_notify_resume(struct pt_regs *regs, void *unused,
                       __u32 thread_info_flags)
 {
-        /* Pending single-step? */
-        if (thread_info_flags & _TIF_SINGLESTEP) {
-                regs->flags |= X86_EFLAGS_TF;
-                clear_thread_flag(TIF_SINGLESTEP);
-        }
-
 #ifdef CONFIG_X86_MCE
         /* notify userspace of pending MCEs */
         if (thread_info_flags & _TIF_MCE_NOTIFY)
diff --git a/include/asm-x86/thread_info.h b/include/asm-x86/thread_info.h
index 895339d2bc0b..fb8d3cdf143e 100644
--- a/include/asm-x86/thread_info.h
+++ b/include/asm-x86/thread_info.h
@@ -124,7 +124,7 @@ struct thread_info {
 /* work to do on interrupt/exception return */
 #define _TIF_WORK_MASK                                                  \
         (0x0000FFFF &                                                   \
-         ~(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP|       \
+         ~(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|                       \
          _TIF_SECCOMP|_TIF_SYSCALL_EMU))
 
 /* work to do on any return to user space */
@@ -132,7 +132,7 @@ struct thread_info {
 
 /* Only used for 64 bit */
 #define _TIF_DO_NOTIFY_MASK                                             \
-        (_TIF_SIGPENDING|_TIF_SINGLESTEP|_TIF_MCE_NOTIFY|_TIF_HRTICK_RESCHED)
+        (_TIF_SIGPENDING|_TIF_MCE_NOTIFY|_TIF_HRTICK_RESCHED)
 
 /* flags to check in __switch_to() */
 #define _TIF_WORK_CTXSW                                                 \