x86/entry/32: Fix FS and GS restore in opportunistic SYSEXIT

We either need to restore them before popping and thus changing
ESP, or we need to adjust the offsets.  The former is simpler.

Reported-and-tested-by: Borislav Petkov <bp@suse.de>
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: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 5f310f739b4c x86/entry/32: ("Re-implement SYSENTER using the new C path")
Link: http://lkml.kernel.org/r/461e5c7d8fa3821529893a4893ac9c4bc37f9e17.1445035014.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 4f97f49261d365a3bcce383adc749e8a0eec4c34..3eb572ed3d7ad438d8dfd1627b5b4121314c9f67 100644 (file)
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -315,14 +315,14 @@ sysenter_past_esp:
        TRACE_IRQS_ON                   /* User mode traces as IRQs on. */
        movl    PT_EIP(%esp), %edx      /* pt_regs->ip */
        movl    PT_OLDESP(%esp), %ecx   /* pt_regs->sp */
+1:     mov     PT_FS(%esp), %fs
+       PTGS_TO_GS
        popl    %ebx                    /* pt_regs->bx */
        addl    $2*4, %esp              /* skip pt_regs->cx and pt_regs->dx */
        popl    %esi                    /* pt_regs->si */
        popl    %edi                    /* pt_regs->di */
        popl    %ebp                    /* pt_regs->bp */
        popl    %eax                    /* pt_regs->ax */
-1:     mov     PT_FS(%esp), %fs
-       PTGS_TO_GS
 
        /*
         * Return back to the vDSO, which will pop ecx and edx.