x86: make traps on 'iret' be debuggable in user space

This makes a trap on the 'iret' that returns us to user space
cause a nice clean SIGSEGV, instead of just a hard (and silent)
exit.

That way a debugger can actually try to see what happened, and
we also properly notify everybody who might be interested about
us being gone.

This loses the error code, but tells the debugger what happened
with ILL_BADSTK in the siginfo.

diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S
index 3c73dc865ead3ad2323098a3b78b0fc8042e7489..fe1918cc68d1f343e7857dd86b66488f4ff1938c 100644 (file)
--- a/arch/i386/kernel/entry.S
+++ b/arch/i386/kernel/entry.S
@@ -260,11 +260,9 @@ restore_nocheck:
 .section .fixup,"ax"
 iret_exc:
        sti
-       movl $__USER_DS, %edx
-       movl %edx, %ds
-       movl %edx, %es
-       movl $11,%eax
-       call do_exit
+       pushl $0                        # no error code
+       pushl $do_iret_error
+       jmp error_code
 .previous
 .section __ex_table,"a"
        .align 4

diff --git a/arch/i386/kernel/traps.c b/arch/i386/kernel/traps.c
index 6c0e383915b6a0d9fc516a04f328020d18b575b5..d70819481f6eb1af7de9b4bc5c05e7d78b0a43af 100644 (file)
--- a/arch/i386/kernel/traps.c
+++ b/arch/i386/kernel/traps.c
@@ -451,6 +451,7 @@ DO_ERROR(10, SIGSEGV, "invalid TSS", invalid_TSS)
 DO_ERROR(11, SIGBUS,  "segment not present", segment_not_present)
 DO_ERROR(12, SIGBUS,  "stack segment", stack_segment)
 DO_ERROR_INFO(17, SIGBUS, "alignment check", alignment_check, BUS_ADRALN, 0)
+DO_ERROR_INFO(32, SIGSEGV, "iret exception", iret_error, ILL_BADSTK, 0)
 
 fastcall void do_general_protection(struct pt_regs * regs, long error_code)
 {