This closes some arcane holes in single-step handling that can arise
only when user programs set TF directly (via popf or sigreturn) and
then use vDSO (syscall/sysenter) system call entry. In those entry
paths, the clear_TF_reenable case hits and we must check TIF_SINGLESTEP
to be sure our bookkeeping stays correct wrt the user's view of TF.
Signed-off-by: Roland McGrath <roland@redhat.com>
---
arch/x86/kernel/ptrace.c | 10 ++++++++++
arch/x86/kernel/step.c | 13 +++++++++++++
include/asm-x86/thread_info.h | 2 +-
3 files changed, 24 insertions(+), 1 deletions(-)
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 34e77b1..e37dccc 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -1416,6 +1416,16 @@ asmregparm long syscall_trace_enter(struct pt_regs *regs)
{
long ret = 0;
+ /*
+ * If we stepped into a sysenter/syscall insn, it trapped in
+ * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
+ * If user-mode had set TF itself, then it's still clear from
+ * do_debug() and we need to set it again to restore the user
+ * state. If we entered on the slow path, TF was already set.
+ */
+ if (test_thread_flag(TIF_SINGLESTEP))
+ regs->flags |= X86_EFLAGS_TF;
+
/* do the secure computing check first */
secure_computing(regs->orig_ax);
diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index 0d2cb36..e8b9863 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -108,6 +108,19 @@ static int enable_single_step(struct task_struct *child)
unsigned long oflags;
/*
+ * If we stepped into a sysenter/syscall insn, it trapped in
+ * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
+ * If user-mode had set TF itself, then it's still clear from
+ * do_debug() and we need to set it again to restore the user
+ * state so we don't wrongly set TIF_FORCED_TF below.
+ * If enable_single_step() was used last and that is what
+ * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are
+ * already set and our bookkeeping is fine.
+ */
+ if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP)))
+ regs->flags |= X86_EFLAGS_TF;
+
+ /*
* Always set TIF_SINGLESTEP - this guarantees that
* we single-step system calls etc.. This will also
* cause us to set TF when returning to user mode.
diff --git a/include/asm-x86/thread_info.h b/include/asm-x86/thread_info.h
index b2702a1..0a8f27d 100644
--- a/include/asm-x86/thread_info.h
+++ b/include/asm-x86/thread_info.h
@@ -118,7 +118,7 @@ struct thread_info {
/* work to do in syscall_trace_enter() */
#define _TIF_WORK_SYSCALL_ENTRY \
(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU | \
- _TIF_SYSCALL_AUDIT | _TIF_SECCOMP)
+ _TIF_SYSCALL_AUDIT | _TIF_SECCOMP | _TIF_SINGLESTEP)
/* work to do in syscall_trace_leave() */
#define _TIF_WORK_SYSCALL_EXIT \
--
