Fix an API loophole introduced with commit 9791554b45a2 ("MIPS,prctl: add PR_[GS]ET_FP_MODE prctl options for MIPS"), where the caller of prctl(2) is incorrectly allowed to make a change to CP0.Status.FR or CP0.Config5.FRE register bits even if CONFIG_MIPS_O32_FP64_SUPPORT has not been enabled, despite that an executable requesting the mode requested via ELF file annotation would not be allowed to run in the first place, or for n64 and n64 ABI tasks which do not have non-default modes defined at all. Add suitable checks to `mips_set_process_fp_mode' and bail out if an invalid mode change has been requested for the ABI in effect, even if the FPU hardware or emulation would otherwise allow it.
Always succeed however without taking any further action if the mode requested is the same as one already in effect, regardless of whether any mode change, should it be requested, would actually be allowed for the task concerned.
Cc: stable@vger.kernel.org # 4.0+ Fixes: 9791554b45a2 ("MIPS,prctl: add PR_[GS]ET_FP_MODE prctl options for MIPS") Signed-off-by: Maciej W. Rozycki macro@mips.com --- arch/mips/kernel/process.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
linux-mips-prctl-fp-mode-o32-fp64.diff Index: linux-sfr-test/arch/mips/kernel/process.c =================================================================== --- linux-sfr-test.orig/arch/mips/kernel/process.c 2017-11-25 12:40:55.868109000 +0000 +++ linux-sfr-test/arch/mips/kernel/process.c 2017-11-25 12:41:56.411578000 +0000 @@ -705,6 +705,18 @@ int mips_set_process_fp_mode(struct task struct task_struct *t; int max_users;
+ /* If nothing to change, return right away, successfully. */ + if (value == mips_get_process_fp_mode(task)) + return 0; + + /* Only accept a mode change if 64-bit FP enabled for o32. */ + if (!IS_ENABLED(CONFIG_MIPS_O32_FP64_SUPPORT)) + return -EOPNOTSUPP; + + /* And only for o32 tasks. */ + if (IS_ENABLED(CONFIG_64BIT) && !test_thread_flag(TIF_32BIT_REGS)) + return -EOPNOTSUPP; + /* Check the value is valid */ if (value & ~known_bits) return -EOPNOTSUPP;