releases/4.9.107/mips-prctl-disallow-fre-without-fr-with-pr_set_fp_mode-requests.patch

   1 From 28e4213dd331e944e7fca1954a946829162ed9d4 Mon Sep 17 00:00:00 2001
   2 From: "Maciej W. Rozycki" <macro@mips.com>
   3 Date: Tue, 15 May 2018 23:04:44 +0100
   4 Subject: MIPS: prctl: Disallow FRE without FR with PR_SET_FP_MODE requests
   5
   6 From: Maciej W. Rozycki <macro@mips.com>
   7
   8 commit 28e4213dd331e944e7fca1954a946829162ed9d4 upstream.
   9
  10 Having PR_FP_MODE_FRE (i.e. Config5.FRE) set without PR_FP_MODE_FR (i.e.
  11 Status.FR) is not supported as the lone purpose of Config5.FRE is to
  12 emulate Status.FR=0 handling on FPU hardware that has Status.FR=1
  13 hardwired[1][2].  Also we do not handle this case elsewhere, and assume
  14 throughout our code that TIF_HYBRID_FPREGS and TIF_32BIT_FPREGS cannot
  15 be set both at once for a task, leading to inconsistent behaviour if
  16 this does happen.
  17
  18 Return unsuccessfully then from prctl(2) PR_SET_FP_MODE calls requesting
  19 PR_FP_MODE_FRE to be set with PR_FP_MODE_FR clear.  This corresponds to
  20 modes allowed by `mips_set_personality_fp'.
  21
  22 References:
  23
  24 [1] "MIPS Architecture For Programmers, Vol. III: MIPS32 / microMIPS32
  25     Privileged Resource Architecture", Imagination Technologies,
  26     Document Number: MD00090, Revision 6.02, July 10, 2015, Table 9.69
  27     "Config5 Register Field Descriptions", p. 262
  28
  29 [2] "MIPS Architecture For Programmers, Volume III: MIPS64 / microMIPS64
  30     Privileged Resource Architecture", Imagination Technologies,
  31     Document Number: MD00091, Revision 6.03, December 22, 2015, Table
  32     9.72 "Config5 Register Field Descriptions", p. 288
  33
  34 Fixes: 9791554b45a2 ("MIPS,prctl: add PR_[GS]ET_FP_MODE prctl options for MIPS")
  35 Signed-off-by: Maciej W. Rozycki <macro@mips.com>
  36 Cc: Ralf Baechle <ralf@linux-mips.org>
  37 Cc: linux-mips@linux-mips.org
  38 Cc: <stable@vger.kernel.org> # 4.0+
  39 Patchwork: https://patchwork.linux-mips.org/patch/19327/
  40 Signed-off-by: James Hogan <jhogan@kernel.org>
  41 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  42
  43 ---
  44  arch/mips/kernel/process.c |    4 ++++
  45  1 file changed, 4 insertions(+)
  46
  47 --- a/arch/mips/kernel/process.c
  48 +++ b/arch/mips/kernel/process.c
  49 @@ -699,6 +699,10 @@ int mips_set_process_fp_mode(struct task
  50         if (value & ~known_bits)
  51                 return -EOPNOTSUPP;
  52
  53 +       /* Setting FRE without FR is not supported.  */
  54 +       if ((value & (PR_FP_MODE_FR | PR_FP_MODE_FRE)) == PR_FP_MODE_FRE)
  55 +               return -EOPNOTSUPP;
  56 +
  57         /* Avoid inadvertently triggering emulation */
  58         if ((value & PR_FP_MODE_FR) && raw_cpu_has_fpu &&
  59             !(raw_current_cpu_data.fpu_id & MIPS_FPIR_F64))