kgdb, x86, arm, mips, powerpc: ignore user space single stepping

On the x86 arch, user space single step exceptions should be ignored
if they occur in the kernel space, such as ptrace stepping through a
system call.

First check if it is kgdb that is executing a single step, then ensure
it is not an accidental traversal into the user space, while in kgdb,
any other time the TIF_SINGLESTEP is set, kgdb should ignore the
exception.

On x86, arm, mips and powerpc, the kgdb_contthread usage was
inconsistent with the way single stepping is implemented in the kgdb
core.  The arch specific stub should always set the
kgdb_cpu_doing_single_step correctly if it is single stepping.  This
allows kgdb to correctly process an instruction steps if ptrace
happens to be requesting an instruction step over a system call.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/kernel/kgdb.c b/kernel/kgdb.c
index 949806ab67d..25d955dbb98 100644
--- a/kernel/kgdb.c
+++ b/kernel/kgdb.c
@@ -1462,7 +1462,7 @@ acquirelock:
          * Get the passive CPU lock which will hold all the non-primary
          * CPU in a spin state while the debugger is active
          */
-        if (!kgdb_single_step || !kgdb_contthread) {
+        if (!kgdb_single_step) {
                 for (i = 0; i < NR_CPUS; i++)
                         atomic_set(&passive_cpu_wait[i], 1);
         }
@@ -1475,7 +1475,7 @@ acquirelock:
 
 #ifdef CONFIG_SMP
         /* Signal the other CPUs to enter kgdb_wait() */
-        if ((!kgdb_single_step || !kgdb_contthread) && kgdb_do_roundup)
+        if ((!kgdb_single_step) && kgdb_do_roundup)
                 kgdb_roundup_cpus(flags);
 #endif
 
@@ -1494,7 +1494,7 @@ acquirelock:
         kgdb_post_primary_code(ks->linux_regs, ks->ex_vector, ks->err_code);
         kgdb_deactivate_sw_breakpoints();
         kgdb_single_step = 0;
-        kgdb_contthread = NULL;
+        kgdb_contthread = current;
         exception_level = 0;
 
         /* Talk to debugger with gdbserial protocol */
@@ -1508,7 +1508,7 @@ acquirelock:
         kgdb_info[ks->cpu].task = NULL;
         atomic_set(&cpu_in_kgdb[ks->cpu], 0);
 
-        if (!kgdb_single_step || !kgdb_contthread) {
+        if (!kgdb_single_step) {
                 for (i = NR_CPUS-1; i >= 0; i--)
                         atomic_set(&passive_cpu_wait[i], 0);
                 /*