kgdb,i386: Fix corner case access to ss with NMI watch dog exception

It is possible for the user_mode_vm(regs) check to return true on the
i368 arch for a non master kgdb cpu or when the master kgdb cpu
handles the NMI watch dog exception.

The solution is simply to select the correct gdb_ss location
based on the check to user_mode_vm(regs).

CC: Ingo Molnar <mingo@elte.hu>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index f93d015753ce..aefae46aa646 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -86,9 +86,15 @@ void pt_regs_to_gdb_regs(unsigned long *gdb_regs, struct pt_regs *regs)
         gdb_regs[GDB_DS]        = regs->ds;
         gdb_regs[GDB_ES]        = regs->es;
         gdb_regs[GDB_CS]        = regs->cs;
-        gdb_regs[GDB_SS]        = __KERNEL_DS;
         gdb_regs[GDB_FS]        = 0xFFFF;
         gdb_regs[GDB_GS]        = 0xFFFF;
+        if (user_mode_vm(regs)) {
+                gdb_regs[GDB_SS] = regs->ss;
+                gdb_regs[GDB_SP] = regs->sp;
+        } else {
+                gdb_regs[GDB_SS] = __KERNEL_DS;
+                gdb_regs[GDB_SP] = kernel_stack_pointer(regs);
+        }
 #else
         gdb_regs[GDB_R8]        = regs->r8;
         gdb_regs[GDB_R9]        = regs->r9;
@@ -101,8 +107,8 @@ void pt_regs_to_gdb_regs(unsigned long *gdb_regs, struct pt_regs *regs)
         gdb_regs32[GDB_PS]      = regs->flags;
         gdb_regs32[GDB_CS]      = regs->cs;
         gdb_regs32[GDB_SS]      = regs->ss;
-#endif
         gdb_regs[GDB_SP]        = kernel_stack_pointer(regs);
+#endif
 }
 
 /**