3 files changed, 107 insertions, 14 deletions

diff --git a/arch/mips/include/asm/elf.h b/arch/mips/include/asm/elf.h
index 3dba5d05830c..cefb7a596878 100644
--- a/arch/mips/include/asm/elf.h
+++ b/arch/mips/include/asm/elf.h
@@ -447,6 +447,10 @@ struct arch_elf_state {
 	.overall_fp_mode = -1,			\
 }
 
+/* Whether to accept legacy-NaN and 2008-NaN user binaries.  */
+extern bool mips_use_nan_legacy;
+extern bool mips_use_nan_2008;
+
 extern int arch_elf_pt_proc(void *ehdr, void *phdr, struct file *elf,
 			    bool is_interp, struct arch_elf_state *state);
 
diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c
index 0aa61a95eb4b..b725b713b9f8 100644
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -151,26 +151,109 @@ static void cpu_set_fpu_2008(struct cpuinfo_mips *c)
 }
 
 /*
- * Set the IEEE 754 NaN encodings and ABS.fmt/NEG.fmt execution modes
- * for the FPU emulator.  Clear the flags where required in case called
- * from `fpu_disable', to override details obtained from FPU hardware.
+ * IEEE 754 conformance mode to use.  Affects the NaN encoding and the
+ * ABS.fmt/NEG.fmt execution mode.
+ */
+static enum { STRICT, LEGACY, STD2008, RELAXED } ieee754 = STRICT;
+
+/*
+ * Set the IEEE 754 NaN encodings and the ABS.fmt/NEG.fmt execution modes
+ * to support by the FPU emulator according to the IEEE 754 conformance
+ * mode selected.  Note that "relaxed" straps the emulator so that it
+ * allows 2008-NaN binaries even for legacy processors.
  */
 static void cpu_set_nofpu_2008(struct cpuinfo_mips *c)
 {
+	c->options &= ~(MIPS_CPU_NAN_2008 | MIPS_CPU_NAN_LEGACY);
 	c->fpu_csr31 &= ~(FPU_CSR_ABS2008 | FPU_CSR_NAN2008);
-	if (c->isa_level & (MIPS_CPU_ISA_M32R1 | MIPS_CPU_ISA_M64R1 |
-			    MIPS_CPU_ISA_M32R2 | MIPS_CPU_ISA_M64R2 |
-			    MIPS_CPU_ISA_M32R6 | MIPS_CPU_ISA_M64R6)) {
-		c->options |= MIPS_CPU_NAN_2008 | MIPS_CPU_NAN_LEGACY;
-		c->fpu_msk31 &= ~(FPU_CSR_ABS2008 | FPU_CSR_NAN2008);
-	} else {
-		c->options &= ~MIPS_CPU_NAN_2008;
+	c->fpu_msk31 &= ~(FPU_CSR_ABS2008 | FPU_CSR_NAN2008);
+
+	switch (ieee754) {
+	case STRICT:
+		if (c->isa_level & (MIPS_CPU_ISA_M32R1 | MIPS_CPU_ISA_M64R1 |
+				    MIPS_CPU_ISA_M32R2 | MIPS_CPU_ISA_M64R2 |
+				    MIPS_CPU_ISA_M32R6 | MIPS_CPU_ISA_M64R6)) {
+			c->options |= MIPS_CPU_NAN_2008 | MIPS_CPU_NAN_LEGACY;
+		} else {
+			c->options |= MIPS_CPU_NAN_LEGACY;
+			c->fpu_msk31 |= FPU_CSR_ABS2008 | FPU_CSR_NAN2008;
+		}
+		break;
+	case LEGACY:
 		c->options |= MIPS_CPU_NAN_LEGACY;
 		c->fpu_msk31 |= FPU_CSR_ABS2008 | FPU_CSR_NAN2008;
+		break;
+	case STD2008:
+		c->options |= MIPS_CPU_NAN_2008;
+		c->fpu_csr31 |= FPU_CSR_ABS2008 | FPU_CSR_NAN2008;
+		c->fpu_msk31 |= FPU_CSR_ABS2008 | FPU_CSR_NAN2008;
+		break;
+	case RELAXED:
+		c->options |= MIPS_CPU_NAN_2008 | MIPS_CPU_NAN_LEGACY;
+		break;
+	}
+}
+
+/*
+ * Override the IEEE 754 NaN encoding and ABS.fmt/NEG.fmt execution mode
+ * according to the "ieee754=" parameter.
+ */
+static void cpu_set_nan_2008(struct cpuinfo_mips *c)
+{
+	switch (ieee754) {
+	case STRICT:
+		mips_use_nan_legacy = !!cpu_has_nan_legacy;
+		mips_use_nan_2008 = !!cpu_has_nan_2008;
+		break;
+	case LEGACY:
+		mips_use_nan_legacy = !!cpu_has_nan_legacy;
+		mips_use_nan_2008 = !cpu_has_nan_legacy;
+		break;
+	case STD2008:
+		mips_use_nan_legacy = !cpu_has_nan_2008;
+		mips_use_nan_2008 = !!cpu_has_nan_2008;
+		break;
+	case RELAXED:
+		mips_use_nan_legacy = true;
+		mips_use_nan_2008 = true;
+		break;
 	}
 }
 
 /*
+ * IEEE 754 NaN encoding and ABS.fmt/NEG.fmt execution mode override
+ * settings:
+ *
+ * strict:  accept binaries that request a NaN encoding supported by the FPU
+ * legacy:  only accept legacy-NaN binaries
+ * 2008:    only accept 2008-NaN binaries
+ * relaxed: accept any binaries regardless of whether supported by the FPU
+ */
+static int __init ieee754_setup(char *s)
+{
+	if (!s)
+		return -1;
+	else if (!strcmp(s, "strict"))
+		ieee754 = STRICT;
+	else if (!strcmp(s, "legacy"))
+		ieee754 = LEGACY;
+	else if (!strcmp(s, "2008"))
+		ieee754 = STD2008;
+	else if (!strcmp(s, "relaxed"))
+		ieee754 = RELAXED;
+	else
+		return -1;
+
+	if (!(boot_cpu_data.options & MIPS_CPU_FPU))
+		cpu_set_nofpu_2008(&boot_cpu_data);
+	cpu_set_nan_2008(&boot_cpu_data);
+
+	return 0;
+}
+
+early_param("ieee754", ieee754_setup);
+
+/*
  * Set the FIR feature flags for the FPU emulator.
  */
 static void cpu_set_nofpu_id(struct cpuinfo_mips *c)
@@ -212,6 +295,7 @@ static void cpu_set_fpu_opts(struct cpuinfo_mips *c)
 
 	cpu_set_fpu_fcsr_mask(c);
 	cpu_set_fpu_2008(c);
+	cpu_set_nan_2008(c);
 }
 
 /*
@@ -223,6 +307,7 @@ static void cpu_set_nofpu_opts(struct cpuinfo_mips *c)
 	c->fpu_msk31 = mips_nofpu_msk31;
 
 	cpu_set_nofpu_2008(c);
+	cpu_set_nan_2008(c);
 	cpu_set_nofpu_id(c);
 }
 
diff --git a/arch/mips/kernel/elf.c b/arch/mips/kernel/elf.c
index f36a261b275c..c3c234dc0c07 100644
--- a/arch/mips/kernel/elf.c
+++ b/arch/mips/kernel/elf.c
@@ -13,6 +13,10 @@
 
 #include <asm/cpu-info.h>
 
+/* Whether to accept legacy-NaN and 2008-NaN user binaries.  */
+bool mips_use_nan_legacy;
+bool mips_use_nan_2008;
+
 /* FPU modes */
 enum {
 	FP_FRE,
@@ -150,16 +154,16 @@ int arch_check_elf(void *_ehdr, bool has_interpreter, void *_interp_ehdr,
 	flags = elf32 ? ehdr->e32.e_flags : ehdr->e64.e_flags;
 
 	/*
-	 * Determine the NaN personality, reject the binary if no hardware
-	 * support.  Also ensure that any interpreter matches the executable.
+	 * Determine the NaN personality, reject the binary if not allowed.
+	 * Also ensure that any interpreter matches the executable.
 	 */
 	if (flags & EF_MIPS_NAN2008) {
-		if (cpu_has_nan_2008)
+		if (mips_use_nan_2008)
 			state->nan_2008 = 1;
 		else
 			return -ENOEXEC;
 	} else {
-		if (cpu_has_nan_legacy)
+		if (mips_use_nan_legacy)
 			state->nan_2008 = 0;
 		else
 			return -ENOEXEC;