x86/entry/64: Really create an error-entry-from-usermode code path

In 539f51136500 ("x86/asm/entry/64: Disentangle error_entry/exit
gsbase/ebx/usermode code"), I arranged the code slightly wrong
-- IRET faults would skip the code path that was intended to
execute on all error entries from user mode.  Fix it up.

While we're at it, make all the labels in error_entry local.

This does not fix a bug, but we'll need it, and it slightly
shrinks the code.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/91e17891e49fa3d61357eadc451529ad48143ee1.1435952415.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 141a5d49dddc5c7d487d724098cd37080656d3d1..ccfcba90de6e73499cd5468e5ae11d045ec09f21 100644 (file)
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1143,12 +1143,17 @@ ENTRY(error_entry)
        SAVE_EXTRA_REGS 8
        xorl    %ebx, %ebx
        testb   $3, CS+8(%rsp)
-       jz      error_kernelspace
+       jz      .Lerror_kernelspace
 
-       /* We entered from user mode */
+.Lerror_entry_from_usermode_swapgs:
+       /*
+        * We entered from user mode or we're pretending to have entered
+        * from user mode due to an IRET fault.
+        */
        SWAPGS
 
-error_entry_done:
+.Lerror_entry_from_usermode_after_swapgs:
+.Lerror_entry_done:
        TRACE_IRQS_OFF
        ret
 
@@ -1158,31 +1163,30 @@ error_entry_done:
         * truncated RIP for IRET exceptions returning to compat mode. Check
         * for these here too.
         */
-error_kernelspace:
+.Lerror_kernelspace:
        incl    %ebx
        leaq    native_irq_return_iret(%rip), %rcx
        cmpq    %rcx, RIP+8(%rsp)
-       je      error_bad_iret
+       je      .Lerror_bad_iret
        movl    %ecx, %eax                      /* zero extend */
        cmpq    %rax, RIP+8(%rsp)
-       je      bstep_iret
+       je      .Lbstep_iret
        cmpq    $gs_change, RIP+8(%rsp)
-       jne     error_entry_done
+       jne     .Lerror_entry_done
 
        /*
         * hack: gs_change can fail with user gsbase.  If this happens, fix up
         * gsbase and proceed.  We'll fix up the exception and land in
         * gs_change's error handler with kernel gsbase.
         */
-       SWAPGS
-       jmp     error_entry_done
+       jmp     .Lerror_entry_from_usermode_swapgs
 
-bstep_iret:
+.Lbstep_iret:
        /* Fix truncated RIP */
        movq    %rcx, RIP+8(%rsp)
        /* fall through */
 
-error_bad_iret:
+.Lerror_bad_iret:
        /*
         * We came from an IRET to user mode, so we have user gsbase.
         * Switch to kernel gsbase:
@@ -1198,7 +1202,7 @@ error_bad_iret:
        call    fixup_bad_iret
        mov     %rax, %rsp
        decl    %ebx
-       jmp     error_entry_done
+       jmp     .Lerror_entry_from_usermode_after_swapgs
 END(error_entry)