From 28e4213dd331e944e7fca1954a946829162ed9d4 Mon Sep 17 00:00:00 2001 From: "Maciej W. Rozycki" Date: Tue, 15 May 2018 23:04:44 +0100 Subject: MIPS: prctl: Disallow FRE without FR with PR_SET_FP_MODE requests Having PR_FP_MODE_FRE (i.e. Config5.FRE) set without PR_FP_MODE_FR (i.e. Status.FR) is not supported as the lone purpose of Config5.FRE is to emulate Status.FR=0 handling on FPU hardware that has Status.FR=1 hardwired[1][2]. Also we do not handle this case elsewhere, and assume throughout our code that TIF_HYBRID_FPREGS and TIF_32BIT_FPREGS cannot be set both at once for a task, leading to inconsistent behaviour if this does happen. Return unsuccessfully then from prctl(2) PR_SET_FP_MODE calls requesting PR_FP_MODE_FRE to be set with PR_FP_MODE_FR clear. This corresponds to modes allowed by `mips_set_personality_fp'. References: [1] "MIPS Architecture For Programmers, Vol. III: MIPS32 / microMIPS32 Privileged Resource Architecture", Imagination Technologies, Document Number: MD00090, Revision 6.02, July 10, 2015, Table 9.69 "Config5 Register Field Descriptions", p. 262 [2] "MIPS Architecture For Programmers, Volume III: MIPS64 / microMIPS64 Privileged Resource Architecture", Imagination Technologies, Document Number: MD00091, Revision 6.03, December 22, 2015, Table 9.72 "Config5 Register Field Descriptions", p. 288 Fixes: 9791554b45a2 ("MIPS,prctl: add PR_[GS]ET_FP_MODE prctl options for MIPS") Signed-off-by: Maciej W. Rozycki Cc: Ralf Baechle Cc: linux-mips@linux-mips.org Cc: # 4.0+ Patchwork: https://patchwork.linux-mips.org/patch/19327/ Signed-off-by: James Hogan --- arch/mips/kernel/process.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'arch/mips') diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c index b9e9bf628849..3775a8d694fb 100644 --- a/arch/mips/kernel/process.c +++ b/arch/mips/kernel/process.c @@ -721,6 +721,10 @@ int mips_set_process_fp_mode(struct task_struct *task, unsigned int value) if (value & ~known_bits) return -EOPNOTSUPP; + /* Setting FRE without FR is not supported. */ + if ((value & (PR_FP_MODE_FR | PR_FP_MODE_FRE)) == PR_FP_MODE_FRE) + return -EOPNOTSUPP; + /* Avoid inadvertently triggering emulation */ if ((value & PR_FP_MODE_FR) && raw_cpu_has_fpu && !(raw_current_cpu_data.fpu_id & MIPS_FPIR_F64)) -- cgit v1.2.3