powerpc: Emulate FP/vector/VSX loads/stores correctly when regs not live

At present, the analyse_instr/emulate_step code checks for the
relevant MSR_FP/VEC/VSX bit being set when a FP/VMX/VSX load
or store is decoded, but doesn't recheck the bit before reading or
writing the relevant FP/VMX/VSX register in emulate_step().

Since we don't have preemption disabled, it is possible that we get
preempted between checking the MSR bit and doing the register access.
If that happened, then the registers would have been saved to the
thread_struct for the current process.  Accesses to the CPU registers
would then potentially read stale values, or write values that would
never be seen by the user process.

Another way that the registers can become non-live is if a page
fault occurs when accessing user memory, and the page fault code
calls a copy routine that wants to use the VMX or VSX registers.

To fix this, the code for all the FP/VMX/VSX loads gets restructured
so that it forms an image in a local variable of the desired register
contents, then disables preemption, checks the MSR bit and either
sets the CPU register or writes the value to the thread struct.
Similarly, the code for stores checks the MSR bit, copies either the
CPU register or the thread struct to a local variable, then reenables
preemption and then copies the register image to memory.

If the instruction being emulated is in the kernel, then we must not
use the register values in the thread_struct.  In this case, if the
relevant MSR enable bit is not set, then emulate_step refuses to
emulate the instruction.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 159 insertions, 69 deletions

diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index 25ee04321870..c4d6a02a9d1a 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -36,12 +36,10 @@ extern char system_call_common[];
 /*
  * Functions in ldstfp.S
  */
-extern int do_lfs(int rn, unsigned long ea);
-extern int do_lfd(int rn, unsigned long ea);
-extern int do_stfs(int rn, unsigned long ea);
-extern int do_stfd(int rn, unsigned long ea);
-extern int do_lvx(int rn, unsigned long ea);
-extern int do_stvx(int rn, unsigned long ea);
+extern void get_fpr(int rn, double *p);
+extern void put_fpr(int rn, const double *p);
+extern void get_vr(int rn, __vector128 *p);
+extern void put_vr(int rn, __vector128 *p);
 extern void load_vsrn(int vsr, const void *p);
 extern void store_vsrn(int vsr, void *p);
 extern void conv_sp_to_dp(const float *sp, double *dp);
@@ -409,63 +407,108 @@ NOKPROBE_SYMBOL(write_mem);
 
 #ifdef CONFIG_PPC_FPU
 /*
- * Check the address and alignment, and call func to do the actual
- * load or store.
+ * These access either the real FP register or the image in the
+ * thread_struct, depending on regs->msr & MSR_FP.
  */
-static int do_fp_load(int rn, int (*func)(int, unsigned long),
-				unsigned long ea, int nb,
-				struct pt_regs *regs)
+static int do_fp_load(int rn, unsigned long ea, int nb, struct pt_regs *regs)
 {
 	int err;
-	u8 buf[sizeof(double)] __attribute__((aligned(sizeof(double))));
+	union {
+		float f;
+		double d;
+		unsigned long l;
+		u8 b[sizeof(double)];
+	} u;
 
 	if (!address_ok(regs, ea, nb))
 		return -EFAULT;
-	if (ea & 3) {
-		err = copy_mem_in(buf, ea, nb);
-		if (err)
-			return err;
-		ea = (unsigned long) buf;
-	}
-	return (*func)(rn, ea);
+	err = copy_mem_in(u.b, ea, nb);
+	if (err)
+		return err;
+	preempt_disable();
+	if (nb == 4)
+		conv_sp_to_dp(&u.f, &u.d);
+	if (regs->msr & MSR_FP)
+		put_fpr(rn, &u.d);
+	else
+		current->thread.TS_FPR(rn) = u.l;
+	preempt_enable();
+	return 0;
 }
 NOKPROBE_SYMBOL(do_fp_load);
 
-static int do_fp_store(int rn, int (*func)(int, unsigned long),
-				 unsigned long ea, int nb,
-				 struct pt_regs *regs)
+static int do_fp_store(int rn, unsigned long ea, int nb, struct pt_regs *regs)
 {
-	int err;
-	u8 buf[sizeof(double)] __attribute__((aligned(sizeof(double))));
+	union {
+		float f;
+		double d;
+		unsigned long l;
+		u8 b[sizeof(double)];
+	} u;
 
 	if (!address_ok(regs, ea, nb))
 		return -EFAULT;
-	if ((ea & 3) == 0)
-		return (*func)(rn, ea);
-	err = (*func)(rn, (unsigned long) buf);
-	if (!err)
-		err = copy_mem_out(buf, ea, nb);
-	return err;
+	preempt_disable();
+	if (regs->msr & MSR_FP)
+		get_fpr(rn, &u.d);
+	else
+		u.l = current->thread.TS_FPR(rn);
+	if (nb == 4)
+		conv_dp_to_sp(&u.d, &u.f);
+	preempt_enable();
+	return copy_mem_out(u.b, ea, nb);
 }
 NOKPROBE_SYMBOL(do_fp_store);
 #endif
 
 #ifdef CONFIG_ALTIVEC
 /* For Altivec/VMX, no need to worry about alignment */
-static nokprobe_inline int do_vec_load(int rn, int (*func)(int, unsigned long),
-				 unsigned long ea, struct pt_regs *regs)
+static nokprobe_inline int do_vec_load(int rn, unsigned long ea,
+				       int size, struct pt_regs *regs)
 {
+	int err;
+	union {
+		__vector128 v;
+		u8 b[sizeof(__vector128)];
+	} u = {};
+
 	if (!address_ok(regs, ea & ~0xfUL, 16))
 		return -EFAULT;
-	return (*func)(rn, ea);
+	/* align to multiple of size */
+	ea &= ~(size - 1);
+	err = copy_mem_in(u.b, ea, size);
+	if (err)
+		return err;
+
+	preempt_disable();
+	if (regs->msr & MSR_VEC)
+		put_vr(rn, &u.v);
+	else
+		current->thread.vr_state.vr[rn] = u.v;
+	preempt_enable();
+	return 0;
 }
 
-static nokprobe_inline int do_vec_store(int rn, int (*func)(int, unsigned long),
-				  unsigned long ea, struct pt_regs *regs)
+static nokprobe_inline int do_vec_store(int rn, unsigned long ea,
+					int size, struct pt_regs *regs)
 {
+	union {
+		__vector128 v;
+		u8 b[sizeof(__vector128)];
+	} u;
+
 	if (!address_ok(regs, ea & ~0xfUL, 16))
 		return -EFAULT;
-	return (*func)(rn, ea);
+	/* align to multiple of size */
+	ea &= ~(size - 1);
+
+	preempt_disable();
+	if (regs->msr & MSR_VEC)
+		get_vr(rn, &u.v);
+	else
+		u.v = current->thread.vr_state.vr[rn];
+	preempt_enable();
+	return copy_mem_out(u.b, ea, size);
 }
 #endif /* CONFIG_ALTIVEC */
 
@@ -658,6 +701,68 @@ void emulate_vsx_store(struct instruction_op *op, const union vsx_reg *reg,
 }
 EXPORT_SYMBOL_GPL(emulate_vsx_store);
 NOKPROBE_SYMBOL(emulate_vsx_store);
+
+static nokprobe_inline int do_vsx_load(struct instruction_op *op,
+				       unsigned long ea, struct pt_regs *regs)
+{
+	int reg = op->reg;
+	u8 mem[16];
+	union vsx_reg buf;
+	int size = GETSIZE(op->type);
+
+	if (!address_ok(regs, ea, size) || copy_mem_in(mem, ea, size))
+		return -EFAULT;
+
+	emulate_vsx_load(op, &buf, mem);
+	preempt_disable();
+	if (reg < 32) {
+		/* FP regs + extensions */
+		if (regs->msr & MSR_FP) {
+			load_vsrn(reg, &buf);
+		} else {
+			current->thread.fp_state.fpr[reg][0] = buf.d[0];
+			current->thread.fp_state.fpr[reg][1] = buf.d[1];
+		}
+	} else {
+		if (regs->msr & MSR_VEC)
+			load_vsrn(reg, &buf);
+		else
+			current->thread.vr_state.vr[reg - 32] = buf.v;
+	}
+	preempt_enable();
+	return 0;
+}
+
+static nokprobe_inline int do_vsx_store(struct instruction_op *op,
+					unsigned long ea, struct pt_regs *regs)
+{
+	int reg = op->reg;
+	u8 mem[16];
+	union vsx_reg buf;
+	int size = GETSIZE(op->type);
+
+	if (!address_ok(regs, ea, size))
+		return -EFAULT;
+
+	preempt_disable();
+	if (reg < 32) {
+		/* FP regs + extensions */
+		if (regs->msr & MSR_FP) {
+			store_vsrn(reg, &buf);
+		} else {
+			buf.d[0] = current->thread.fp_state.fpr[reg][0];
+			buf.d[1] = current->thread.fp_state.fpr[reg][1];
+		}
+	} else {
+		if (regs->msr & MSR_VEC)
+			store_vsrn(reg, &buf);
+		else
+			buf.v = current->thread.vr_state.vr[reg - 32];
+	}
+	preempt_enable();
+	emulate_vsx_store(op, &buf, mem);
+	return  copy_mem_out(mem, ea, size);
+}
 #endif /* CONFIG_VSX */
 
 #define __put_user_asmx(x, addr, err, op, cr)		\
@@ -2524,25 +2629,26 @@ int emulate_step(struct pt_regs *regs, unsigned int instr)
 
 #ifdef CONFIG_PPC_FPU
 	case LOAD_FP:
-		if (!(regs->msr & MSR_FP))
+		/*
+		 * If the instruction is in userspace, we can emulate it even
+		 * if the VMX state is not live, because we have the state
+		 * stored in the thread_struct.  If the instruction is in
+		 * the kernel, we must not touch the state in the thread_struct.
+		 */
+		if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_FP))
 			return 0;
-		if (size == 4)
-			err = do_fp_load(op.reg, do_lfs, ea, size, regs);
-		else
-			err = do_fp_load(op.reg, do_lfd, ea, size, regs);
+		err = do_fp_load(op.reg, ea, size, regs);
 		goto ldst_done;
 #endif
 #ifdef CONFIG_ALTIVEC
 	case LOAD_VMX:
-		if (!(regs->msr & MSR_VEC))
+		if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
 			return 0;
-		err = do_vec_load(op.reg, do_lvx, ea, regs);
+		err = do_vec_load(op.reg, ea, size, regs);
 		goto ldst_done;
 #endif
 #ifdef CONFIG_VSX
 	case LOAD_VSX: {
-		u8 mem[16];
-		union vsx_reg buf;
 		unsigned long msrbit = MSR_VSX;
 
 		/*
@@ -2551,14 +2657,9 @@ int emulate_step(struct pt_regs *regs, unsigned int instr)
 		 */
 		if (op.reg >= 32 && (op.vsx_flags & VSX_CHECK_VEC))
 			msrbit = MSR_VEC;
-		if (!(regs->msr & msrbit))
+		if (!(regs->msr & MSR_PR) && !(regs->msr & msrbit))
 			return 0;
-		if (!address_ok(regs, ea, size) ||
-		    copy_mem_in(mem, ea, size))
-			return 0;
-
-		emulate_vsx_load(&op, &buf, mem);
-		load_vsrn(op.reg, &buf);
+		err = do_vsx_load(&op, ea, regs);
 		goto ldst_done;
 	}
 #endif
@@ -2599,25 +2700,20 @@ int emulate_step(struct pt_regs *regs, unsigned int instr)
 
 #ifdef CONFIG_PPC_FPU
 	case STORE_FP:
-		if (!(regs->msr & MSR_FP))
+		if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_FP))
 			return 0;
-		if (size == 4)
-			err = do_fp_store(op.reg, do_stfs, ea, size, regs);
-		else
-			err = do_fp_store(op.reg, do_stfd, ea, size, regs);
+		err = do_fp_store(op.reg, ea, size, regs);
 		goto ldst_done;
 #endif
 #ifdef CONFIG_ALTIVEC
 	case STORE_VMX:
-		if (!(regs->msr & MSR_VEC))
+		if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
 			return 0;
-		err = do_vec_store(op.reg, do_stvx, ea, regs);
+		err = do_vec_store(op.reg, ea, size, regs);
 		goto ldst_done;
 #endif
 #ifdef CONFIG_VSX
 	case STORE_VSX: {
-		u8 mem[16];
-		union vsx_reg buf;
 		unsigned long msrbit = MSR_VSX;
 
 		/*
@@ -2626,15 +2722,9 @@ int emulate_step(struct pt_regs *regs, unsigned int instr)
 		 */
 		if (op.reg >= 32 && (op.vsx_flags & VSX_CHECK_VEC))
 			msrbit = MSR_VEC;
-		if (!(regs->msr & msrbit))
-			return 0;
-		if (!address_ok(regs, ea, size))
-			return 0;
-
-		store_vsrn(op.reg, &buf);
-		emulate_vsx_store(&op, &buf, mem);
-		if (copy_mem_out(mem, ea, size))
+		if (!(regs->msr & MSR_PR) && !(regs->msr & msrbit))
 			return 0;
+		err = do_vsx_store(&op, ea, regs);
 		goto ldst_done;
 	}
 #endif