x86/entry/64/compat: Fix SYSENTER's NT flag before user memory access

Clearing NT is part of the prologue, whereas loading up arg6
makes more sense to think about as part of syscall processing.
Reorder them.

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>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/19eb235828b2d2a52c53459e09f2974e15e65a35.1444091584.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index a9360d40fb7fd5f518077cc2d9aaa63cfd4853aa..e2cca89c1ed33a9f4b5ee00d37c18b39f9c10600 100644 (file)
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -88,15 +88,6 @@ ENTRY(entry_SYSENTER_compat)
        cld
        sub     $(10*8), %rsp /* pt_regs->r8-11, bp, bx, r12-15 not saved */
 
-       /*
-        * no need to do an access_ok check here because rbp has been
-        * 32-bit zero extended
-        */
-       ASM_STAC
-1:     movl    (%rbp), %ebp
-       _ASM_EXTABLE(1b, ia32_badarg)
-       ASM_CLAC
-
        /*
         * Sysenter doesn't filter flags, so we need to clear NT
         * ourselves.  To save a few cycles, we can check whether
@@ -106,6 +97,15 @@ ENTRY(entry_SYSENTER_compat)
        jnz     sysenter_fix_flags
 sysenter_flags_fixed:
 
+       /*
+        * No need to do an access_ok() check here because RBP has been
+        * 32-bit zero extended:
+        */
+       ASM_STAC
+1:     movl    (%rbp), %ebp
+       _ASM_EXTABLE(1b, ia32_badarg)
+       ASM_CLAC
+
        orl     $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
        testl   $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
        jnz     sysenter_tracesys