patches/kernel/0087-x86-entry-64-Split-the-IRET-to-user-and-IRET-to-kern.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Andy Lutomirski <luto@kernel.org>
   3 Date: Thu, 2 Nov 2017 00:58:59 -0700
   4 Subject: [PATCH] x86/entry/64: Split the IRET-to-user and IRET-to-kernel paths
   5 MIME-Version: 1.0
   6 Content-Type: text/plain; charset=UTF-8
   7 Content-Transfer-Encoding: 8bit
   8
   9 CVE-2017-5754
  10
  11 These code paths will diverge soon.
  12
  13 Signed-off-by: Andy Lutomirski <luto@kernel.org>
  14 Cc: Borislav Petkov <bpetkov@suse.de>
  15 Cc: Brian Gerst <brgerst@gmail.com>
  16 Cc: Dave Hansen <dave.hansen@intel.com>
  17 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  18 Cc: Peter Zijlstra <peterz@infradead.org>
  19 Cc: Thomas Gleixner <tglx@linutronix.de>
  20 Link: http://lkml.kernel.org/r/dccf8c7b3750199b4b30383c812d4e2931811509.1509609304.git.luto@kernel.org
  21 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  22 (cherry picked from commit 26c4ef9c49d8a0341f6d97ce2cfdd55d1236ed29)
  23 Signed-off-by: Andy Whitcroft <apw@canonical.com>
  24 Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
  25 (cherry picked from commit 64adfba0aeb668304d171c383ac80b22158ec128)
  26 Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
  27 ---
  28  arch/x86/entry/entry_64.S        | 34 +++++++++++++++++++++++++---------
  29  arch/x86/entry/entry_64_compat.S |  2 +-
  30  arch/x86/kernel/head_64.S        |  2 +-
  31  3 files changed, 27 insertions(+), 11 deletions(-)
  32
  33 diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
  34 index fac354ddf056..e546441fbec3 100644
  35 --- a/arch/x86/entry/entry_64.S
  36 +++ b/arch/x86/entry/entry_64.S
  37 @@ -321,7 +321,7 @@ syscall_return_via_sysret:
  38
  39  opportunistic_sysret_failed:
  40         SWAPGS
  41 -       jmp     restore_regs_and_iret
  42 +       jmp     restore_regs_and_return_to_usermode
  43  END(entry_SYSCALL_64)
  44
  45  ENTRY(stub_ptregs_64)
  46 @@ -423,7 +423,7 @@ ENTRY(ret_from_fork)
  47         call    syscall_return_slowpath /* returns with IRQs disabled */
  48         TRACE_IRQS_ON                   /* user mode is traced as IRQS on */
  49         SWAPGS
  50 -       jmp     restore_regs_and_iret
  51 +       jmp     restore_regs_and_return_to_usermode
  52
  53  1:
  54         /* kernel thread */
  55 @@ -612,7 +612,20 @@ GLOBAL(retint_user)
  56         call    prepare_exit_to_usermode
  57         TRACE_IRQS_IRETQ
  58         SWAPGS
  59 -       jmp     restore_regs_and_iret
  60 +
  61 +GLOBAL(restore_regs_and_return_to_usermode)
  62 +#ifdef CONFIG_DEBUG_ENTRY
  63 +       /* Assert that pt_regs indicates user mode. */
  64 +       testl   $3, CS(%rsp)
  65 +       jnz     1f
  66 +       ud2
  67 +1:
  68 +#endif
  69 +       RESTORE_EXTRA_REGS
  70 +       RESTORE_C_REGS
  71 +       REMOVE_PT_GPREGS_FROM_STACK 8
  72 +       INTERRUPT_RETURN
  73 +
  74
  75  /* Returning to kernel space */
  76  retint_kernel:
  77 @@ -632,11 +645,14 @@ retint_kernel:
  78          */
  79         TRACE_IRQS_IRETQ
  80
  81 -/*
  82 - * At this label, code paths which return to kernel and to user,
  83 - * which come from interrupts/exception and from syscalls, merge.
  84 - */
  85 -GLOBAL(restore_regs_and_iret)
  86 +GLOBAL(restore_regs_and_return_to_kernel)
  87 +#ifdef CONFIG_DEBUG_ENTRY
  88 +       /* Assert that pt_regs indicates kernel mode. */
  89 +       testl   $3, CS(%rsp)
  90 +       jz      1f
  91 +       ud2
  92 +1:
  93 +#endif
  94         RESTORE_EXTRA_REGS
  95         RESTORE_C_REGS
  96         REMOVE_PT_GPREGS_FROM_STACK 8
  97 @@ -1340,7 +1356,7 @@ ENTRY(nmi)
  98          * work, because we don't want to enable interrupts.
  99          */
 100         SWAPGS
 101 -       jmp     restore_regs_and_iret
 102 +       jmp     restore_regs_and_return_to_usermode
 103
 104  .Lnmi_from_kernel:
 105         /*
 106 diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
 107 index d8468ba24be0..2b3a88feaa2b 100644
 108 --- a/arch/x86/entry/entry_64_compat.S
 109 +++ b/arch/x86/entry/entry_64_compat.S
 110 @@ -337,7 +337,7 @@ ENTRY(entry_INT80_compat)
 111         /* Go back to user mode. */
 112         TRACE_IRQS_ON
 113         SWAPGS
 114 -       jmp     restore_regs_and_iret
 115 +       jmp     restore_regs_and_return_to_usermode
 116  END(entry_INT80_compat)
 117
 118         ALIGN
 119 diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
 120 index 4117c1e0b3d2..e785734980ad 100644
 121 --- a/arch/x86/kernel/head_64.S
 122 +++ b/arch/x86/kernel/head_64.S
 123 @@ -311,7 +311,7 @@ early_idt_handler_common:
 124
 125  20:
 126         decl early_recursion_flag(%rip)
 127 -       jmp restore_regs_and_iret
 128 +       jmp restore_regs_and_return_to_kernel
 129  END(early_idt_handler_common)
 130
 131         __INITDATA
 132 --
 133 2.14.2
 134