x86: make traps on entry code be debuggable in user space, 64-bit

Unify the x86-64 behavior for 32-bit processes that set
bogus %cs/%ss values (the only ones that can fault in iret)
match what the native i386 behavior is. (do not kill the task
via do_exit but generate a SIGSEGV signal)

[ tglx@linutronix.de: build fix ]

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index bea8474..e518928 100644 (file)
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -593,13 +593,22 @@ ENTRY(native_iret)
        .quad native_iret, bad_iret
        .previous
        .section .fixup,"ax"
-       /* force a signal here? this matches i386 behaviour */
-       /* running with kernel gs */
 bad_iret:
-       movq $11,%rdi   /* SIGSEGV */
-       TRACE_IRQS_ON
-       ENABLE_INTERRUPTS(CLBR_ANY | ~(CLBR_RDI))
-       jmp do_exit
+       /*
+        * The iret traps when the %cs or %ss being restored is bogus.
+        * We've lost the original trap vector and error code.
+        * #GPF is the most likely one to get for an invalid selector.
+        * So pretend we completed the iret and took the #GPF in user mode.
+        *
+        * We are now running with the kernel GS after exception recovery.
+        * But error_entry expects us to have user GS to match the user %cs,
+        * so swap back.
+        */
+       pushq $0
+
+       SWAPGS
+       jmp general_protection
+
        .previous
 
        /* edi: workmask, edx: work */