x86 single_step: TIF_FORCED_TF
This changes the single-step support to use a new thread_info flag
TIF_FORCED_TF instead of the PT_DTRACE flag in task_struct.ptrace.
This keeps arch implementation uses out of this non-arch field.
This changes the ptrace access to eflags to mask TF and maintain
the TIF_FORCED_TF flag directly if userland sets TF, instead of
relying on ptrace_signal_deliver. The 64-bit and 32-bit kernels
are harmonized on this same behavior. The ptrace_signal_deliver
approach works now, but this change makes the low-level register
access code reliable when called from different contexts than a
ptrace stop, which will be possible in the future.
The 64-bit do_debug exception handler is also changed not to clear TF
from user-mode registers. This matches the 32-bit kernel's behavior.
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/x86/ia32/ptrace32.c b/arch/x86/ia32/ptrace32.c
index 9d754b6..5dee334 100644
--- a/arch/x86/ia32/ptrace32.c
+++ b/arch/x86/ia32/ptrace32.c
@@ -89,6 +89,15 @@
__u64 *flags = &stack[offsetof(struct pt_regs, eflags)/8];
val &= FLAG_MASK;
+ /*
+ * If the user value contains TF, mark that
+ * it was not "us" (the debugger) that set it.
+ * If not, make sure it stays set if we had.
+ */
+ if (val & X86_EFLAGS_TF)
+ clear_tsk_thread_flag(child, TIF_FORCED_TF);
+ else if (test_tsk_thread_flag(child, TIF_FORCED_TF))
+ val |= X86_EFLAGS_TF;
*flags = val | (*flags & ~FLAG_MASK);
break;
}
@@ -179,9 +188,17 @@
R32(eax, rax);
R32(orig_eax, orig_rax);
R32(eip, rip);
- R32(eflags, eflags);
R32(esp, rsp);
+ case offsetof(struct user32, regs.eflags):
+ /*
+ * If the debugger set TF, hide it from the readout.
+ */
+ *val = stack[offsetof(struct pt_regs, eflags)/8];
+ if (test_tsk_thread_flag(child, TIF_FORCED_TF))
+ *val &= ~X86_EFLAGS_TF;
+ break;
+
case offsetof(struct user32, u_debugreg[0]):
*val = child->thread.debugreg0;
break;
@@ -425,4 +442,3 @@
put_task_struct(child);
return ret;
}
-
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 4d66a56..d9905c9 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -817,9 +817,6 @@
(char __user * __user *) regs.edx,
®s);
if (error == 0) {
- task_lock(current);
- current->ptrace &= ~PT_DTRACE;
- task_unlock(current);
/* Make sure we don't return using sysenter.. */
set_thread_flag(TIF_IRET);
}
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index ccc9d68..f7356e5 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -709,11 +709,6 @@
if (IS_ERR(filename))
return error;
error = do_execve(filename, argv, envp, ®s);
- if (error == 0) {
- task_lock(current);
- current->ptrace &= ~PT_DTRACE;
- task_unlock(current);
- }
putname(filename);
return error;
}
diff --git a/arch/x86/kernel/ptrace_32.c b/arch/x86/kernel/ptrace_32.c
index b739608..bc7fd80 100644
--- a/arch/x86/kernel/ptrace_32.c
+++ b/arch/x86/kernel/ptrace_32.c
@@ -104,6 +104,15 @@
break;
case EFL:
value &= FLAG_MASK;
+ /*
+ * If the user value contains TF, mark that
+ * it was not "us" (the debugger) that set it.
+ * If not, make sure it stays set if we had.
+ */
+ if (value & X86_EFLAGS_TF)
+ clear_tsk_thread_flag(child, TIF_FORCED_TF);
+ else if (test_tsk_thread_flag(child, TIF_FORCED_TF))
+ value |= X86_EFLAGS_TF;
value |= get_stack_long(child, EFL_OFFSET) & ~FLAG_MASK;
break;
}
@@ -119,6 +128,14 @@
unsigned long retval = ~0UL;
switch (regno >> 2) {
+ case EFL:
+ /*
+ * If the debugger set TF, hide it from the readout.
+ */
+ retval = get_stack_long(child, EFL_OFFSET);
+ if (test_tsk_thread_flag(child, TIF_FORCED_TF))
+ retval &= ~X86_EFLAGS_TF;
+ break;
case GS:
retval = child->thread.gs;
break;
diff --git a/arch/x86/kernel/ptrace_64.c b/arch/x86/kernel/ptrace_64.c
index 4abfbce..035d53e9 100644
--- a/arch/x86/kernel/ptrace_64.c
+++ b/arch/x86/kernel/ptrace_64.c
@@ -143,6 +143,15 @@
return 0;
case offsetof(struct user_regs_struct, eflags):
value &= FLAG_MASK;
+ /*
+ * If the user value contains TF, mark that
+ * it was not "us" (the debugger) that set it.
+ * If not, make sure it stays set if we had.
+ */
+ if (value & X86_EFLAGS_TF)
+ clear_tsk_thread_flag(child, TIF_FORCED_TF);
+ else if (test_tsk_thread_flag(child, TIF_FORCED_TF))
+ value |= X86_EFLAGS_TF;
tmp = get_stack_long(child, EFL_OFFSET);
tmp &= ~FLAG_MASK;
value |= tmp;
@@ -189,6 +198,17 @@
if (child->thread.gsindex != GS_TLS_SEL)
return 0;
return get_desc_base(&child->thread.tls_array[GS_TLS]);
+ case offsetof(struct user_regs_struct, eflags):
+ /*
+ * If the debugger set TF, hide it from the readout.
+ */
+ regno = regno - sizeof(struct pt_regs);
+ val = get_stack_long(child, regno);
+ if (test_tsk_thread_flag(child, TIF_IA32))
+ val &= 0xffffffff;
+ if (test_tsk_thread_flag(child, TIF_FORCED_TF))
+ val &= ~X86_EFLAGS_TF;
+ return val;
default:
regno = regno - sizeof(struct pt_regs);
val = get_stack_long(child, regno);
diff --git a/arch/x86/kernel/signal_32.c b/arch/x86/kernel/signal_32.c
index 1ac53e9..0a7c812 100644
--- a/arch/x86/kernel/signal_32.c
+++ b/arch/x86/kernel/signal_32.c
@@ -545,14 +545,12 @@
}
/*
- * If TF is set due to a debugger (PT_DTRACE), clear the TF flag so
- * that register information in the sigcontext is correct.
+ * If TF is set due to a debugger (TIF_FORCED_TF), clear the TF
+ * flag so that register information in the sigcontext is correct.
*/
- if (unlikely(regs->eflags & TF_MASK)
- && likely(current->ptrace & PT_DTRACE)) {
- current->ptrace &= ~PT_DTRACE;
- regs->eflags &= ~TF_MASK;
- }
+ if (unlikely(regs->eflags & X86_EFLAGS_TF) &&
+ likely(test_and_clear_thread_flag(TIF_FORCED_TF)))
+ regs->eflags &= ~X86_EFLAGS_TF;
/* Set up the stack frame */
if (ka->sa.sa_flags & SA_SIGINFO)
diff --git a/arch/x86/kernel/signal_64.c b/arch/x86/kernel/signal_64.c
index 38d8064..ab0178e 100644
--- a/arch/x86/kernel/signal_64.c
+++ b/arch/x86/kernel/signal_64.c
@@ -349,16 +349,12 @@
}
/*
- * If TF is set due to a debugger (PT_DTRACE), clear the TF
- * flag so that register information in the sigcontext is
- * correct.
+ * If TF is set due to a debugger (TIF_FORCED_TF), clear the TF
+ * flag so that register information in the sigcontext is correct.
*/
- if (unlikely(regs->eflags & TF_MASK)) {
- if (likely(current->ptrace & PT_DTRACE)) {
- current->ptrace &= ~PT_DTRACE;
- regs->eflags &= ~TF_MASK;
- }
- }
+ if (unlikely(regs->eflags & X86_EFLAGS_TF) &&
+ likely(test_and_clear_thread_flag(TIF_FORCED_TF)))
+ regs->eflags &= ~X86_EFLAGS_TF;
#ifdef CONFIG_IA32_EMULATION
if (test_thread_flag(TIF_IA32)) {
diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index 6732272..243bff6 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -135,7 +135,7 @@
if (is_setting_trap_flag(child, regs))
return;
- child->ptrace |= PT_DTRACE;
+ set_tsk_thread_flag(child, TIF_FORCED_TF);
}
void user_disable_single_step(struct task_struct *child)
@@ -144,9 +144,6 @@
clear_tsk_thread_flag(child, TIF_SINGLESTEP);
/* But touch TF only if it was set by us.. */
- if (child->ptrace & PT_DTRACE) {
- struct pt_regs *regs = task_pt_regs(child);
- regs->eflags &= ~X86_EFLAGS_TF;
- child->ptrace &= ~PT_DTRACE;
- }
+ if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
+ task_pt_regs(child)->eflags &= ~X86_EFLAGS_TF;
}
diff --git a/arch/x86/kernel/traps_64.c b/arch/x86/kernel/traps_64.c
index aa248d7..874aca3 100644
--- a/arch/x86/kernel/traps_64.c
+++ b/arch/x86/kernel/traps_64.c
@@ -865,27 +865,14 @@
tsk->thread.debugreg6 = condition;
- /* Mask out spurious TF errors due to lazy TF clearing */
+
+ /*
+ * Single-stepping through TF: make sure we ignore any events in
+ * kernel space (but re-enable TF when returning to user mode).
+ */
if (condition & DR_STEP) {
- /*
- * The TF error should be masked out only if the current
- * process is not traced and if the TRAP flag has been set
- * previously by a tracing process (condition detected by
- * the PT_DTRACE flag); remember that the i386 TRAP flag
- * can be modified by the process itself in user mode,
- * allowing programs to debug themselves without the ptrace()
- * interface.
- */
if (!user_mode(regs))
goto clear_TF_reenable;
- /*
- * Was the TF flag set by a debugger? If so, clear it now,
- * so that register information is correct.
- */
- if (tsk->ptrace & PT_DTRACE) {
- regs->eflags &= ~TF_MASK;
- tsk->ptrace &= ~PT_DTRACE;
- }
}
/* Ok, finally something we can handle */