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>

1 files changed, 15 insertions, 6 deletions

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index bea8474744ff..e518928114db 100644
--- 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 */