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authorRoland McGrath <roland@redhat.com>2008-07-09 11:39:29 +0200
committerRoland McGrath <roland@redhat.com>2008-07-16 21:15:17 +0200
commit380fdd7585a4c2f41b48925eba85c0654b7b858b (patch)
tree3e405cd6cb0be449671ef28c6275fd7ad6b99295
parentx86 ptrace: unify syscall tracing (diff)
downloadlinux-380fdd7585a4c2f41b48925eba85c0654b7b858b.tar.xz
linux-380fdd7585a4c2f41b48925eba85c0654b7b858b.zip
x86 ptrace: user-sets-TF nits
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>
-rw-r--r--arch/x86/kernel/ptrace.c10
-rw-r--r--arch/x86/kernel/step.c13
-rw-r--r--include/asm-x86/thread_info.h2
3 files changed, 24 insertions, 1 deletions
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 34e77b16a42a..e37dccce85db 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 0d2cb363ea75..e8b9863ef8c4 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 b2702a1eeac1..0a8f27d31d0d 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 \