target/linux/brcm2708/patches-4.9/950-0149-Update-vfpmodule.c.patch

   1 From aa00ca3b0296c40a6b5a1ad32258d5b655a28c70 Mon Sep 17 00:00:00 2001
   2 From: Claggy3 <stephen.maclagan@hotmail.com>
   3 Date: Sat, 11 Feb 2017 14:00:30 +0000
   4 Subject: [PATCH] Update vfpmodule.c
   5
   6 Christopher Alexander Tobias Schulze - May 2, 2015, 11:57 a.m.
   7 This patch fixes a problem with VFP state save and restore related
   8 to exception handling (panic with message "BUG: unsupported FP
   9 instruction in kernel mode") present on VFP11 floating point units
  10 (as used with ARM1176JZF-S CPUs, e.g. on first generation Raspberry
  11 Pi boards). This patch was developed and discussed on
  12
  13    https://github.com/raspberrypi/linux/issues/859
  14
  15 A precondition to see the crashes is that floating point exception
  16 traps are enabled. In this case, the VFP11 might determine that a FPU
  17 operation needs to trap at a point in time when it is not possible to
  18 signal this to the ARM11 core any more. The VFP11 will then set the
  19 FPEXC.EX bit and store the trapped opcode in FPINST. (In some cases,
  20 a second opcode might have been accepted by the VFP11 before the
  21 exception was detected and could be reported to the ARM11 - in this
  22 case, the VFP11 also sets FPEXC.FP2V and stores the second opcode in
  23 FPINST2.)
  24
  25 If FPEXC.EX is set, the VFP11 will "bounce" the next FPU opcode issued
  26 by the ARM11 CPU, which will be seen by the ARM11 as an undefined opcode
  27 trap. The VFP support code examines the FPEXC.EX and FPEXC.FP2V bits
  28 to decide what actions to take, i.e., whether to emulate the opcodes
  29 found in FPINST and FPINST2, and whether to retry the bounced instruction.
  30
  31 If a user space application has left the VFP11 in this "pending trap"
  32 state, the next FPU opcode issued to the VFP11 might actually be the
  33 VSTMIA operation vfp_save_state() uses to store the FPU registers
  34 to memory (in our test cases, when building the signal stack frame).
  35 In this case, the kernel crashes as described above.
  36
  37 This patch fixes the problem by making sure that vfp_save_state() is
  38 always entered with FPEXC.EX cleared. (The current value of FPEXC has
  39 already been saved, so this does not corrupt the context. Clearing
  40 FPEXC.EX has no effects on FPINST or FPINST2. Also note that many
  41 callers already modify FPEXC by setting FPEXC.EN before invoking
  42 vfp_save_state().)
  43
  44 This patch also addresses a second problem related to FPEXC.EX: After
  45 returning from signal handling, the kernel reloads the VFP context
  46 from the user mode stack. However, the current code explicitly clears
  47 both FPEXC.EX and FPEXC.FP2V during reload. As VFP11 requires these
  48 bits to be preserved, this patch disables clearing them for VFP
  49 implementations belonging to architecture 1. There should be no
  50 negative side effects: the user can set both bits by executing FPU
  51 opcodes anyway, and while user code may now place arbitrary values
  52 into FPINST and FPINST2 (e.g., non-VFP ARM opcodes) the VFP support
  53 code knows which instructions can be emulated, and rejects other
  54 opcodes with "unhandled bounce" messages, so there should be no
  55 security impact from allowing reloading FPEXC.EX and FPEXC.FP2V.
  56
  57 Signed-off-by: Christopher Alexander Tobias Schulze <cat.schulze@alice-dsl.net>
  58 ---
  59  arch/arm/vfp/vfpmodule.c | 25 +++++++++++++++++++------
  60  1 file changed, 19 insertions(+), 6 deletions(-)
  61
  62 --- a/arch/arm/vfp/vfpmodule.c
  63 +++ b/arch/arm/vfp/vfpmodule.c
  64 @@ -179,8 +179,11 @@ static int vfp_notifier(struct notifier_
  65                  * case the thread migrates to a different CPU. The
  66                  * restoring is done lazily.
  67                  */
  68 -               if ((fpexc & FPEXC_EN) && vfp_current_hw_state[cpu])
  69 +               if ((fpexc & FPEXC_EN) && vfp_current_hw_state[cpu]) {
  70 +                       /* vfp_save_state oopses on VFP11 if EX bit set */
  71 +                       fmxr(FPEXC, fpexc & ~FPEXC_EX);
  72                         vfp_save_state(vfp_current_hw_state[cpu], fpexc);
  73 +               }
  74  #endif
  75
  76                 /*
  77 @@ -463,13 +466,16 @@ static int vfp_pm_suspend(void)
  78         /* if vfp is on, then save state for resumption */
  79         if (fpexc & FPEXC_EN) {
  80                 pr_debug("%s: saving vfp state\n", __func__);
  81 +               /* vfp_save_state oopses on VFP11 if EX bit set */
  82 +               fmxr(FPEXC, fpexc & ~FPEXC_EX);
  83                 vfp_save_state(&ti->vfpstate, fpexc);
  84
  85                 /* disable, just in case */
  86                 fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
  87         } else if (vfp_current_hw_state[ti->cpu]) {
  88  #ifndef CONFIG_SMP
  89 -               fmxr(FPEXC, fpexc | FPEXC_EN);
  90 +               /* vfp_save_state oopses on VFP11 if EX bit set */
  91 +               fmxr(FPEXC, (fpexc & ~FPEXC_EX) | FPEXC_EN);
  92                 vfp_save_state(vfp_current_hw_state[ti->cpu], fpexc);
  93                 fmxr(FPEXC, fpexc);
  94  #endif
  95 @@ -532,7 +538,8 @@ void vfp_sync_hwstate(struct thread_info
  96                 /*
  97                  * Save the last VFP state on this CPU.
  98                  */
  99 -               fmxr(FPEXC, fpexc | FPEXC_EN);
 100 +               /* vfp_save_state oopses on VFP11 if EX bit set */
 101 +               fmxr(FPEXC, (fpexc & ~FPEXC_EX) | FPEXC_EN);
 102                 vfp_save_state(&thread->vfpstate, fpexc | FPEXC_EN);
 103                 fmxr(FPEXC, fpexc);
 104         }
 105 @@ -604,6 +611,7 @@ int vfp_restore_user_hwstate(struct user
 106         struct vfp_hard_struct *hwstate = &thread->vfpstate.hard;
 107         unsigned long fpexc;
 108         int err = 0;
 109 +       u32 fpsid = fmrx(FPSID);
 110
 111         /* Disable VFP to avoid corrupting the new thread state. */
 112         vfp_flush_hwstate(thread);
 113 @@ -627,8 +635,12 @@ int vfp_restore_user_hwstate(struct user
 114         /* Ensure the VFP is enabled. */
 115         fpexc |= FPEXC_EN;
 116
 117 -       /* Ensure FPINST2 is invalid and the exception flag is cleared. */
 118 -       fpexc &= ~(FPEXC_EX | FPEXC_FP2V);
 119 +       /* Mask FPXEC_EX and FPEXC_FP2V if not required by VFP arch */
 120 +       if ((fpsid & FPSID_ARCH_MASK) != (1 << FPSID_ARCH_BIT)) {
 121 +               /* Ensure FPINST2 is invalid and the exception flag is cleared. */
 122 +               fpexc &= ~(FPEXC_EX | FPEXC_FP2V);
 123 +       }
 124 +
 125         hwstate->fpexc = fpexc;
 126
 127         __get_user_error(hwstate->fpinst, &ufp_exc->fpinst, err);
 128 @@ -698,7 +710,8 @@ void kernel_neon_begin(void)
 129         cpu = get_cpu();
 130
 131         fpexc = fmrx(FPEXC) | FPEXC_EN;
 132 -       fmxr(FPEXC, fpexc);
 133 +       /* vfp_save_state oopses on VFP11 if EX bit set */
 134 +       fmxr(FPEXC, fpexc & ~FPEXC_EX);
 135
 136         /*
 137          * Save the userland NEON/VFP state. Under UP,