x86/fpu: Merge the two code paths in __fpu__restore_sig()

The ia32_fxstate case (32bit with fxsr) and the other (64bit frames or
32bit frames without fxsr) restore both from kernel memory and sanitize
the content.

The !ia32_fxstate version restores missing xstates from "init state"
while the ia32_fxstate doesn't and skips it.

Merge the two code paths and keep the !ia32_fxstate one. Copy only the
user_i387_ia32_struct data structure in the ia32_fxstate.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: kvm ML <kvm@vger.kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190403164156.19645-23-bigeasy@linutronix.de

arch/x86/kernel/fpu/signal.c

@@ -263,12 +263,17 @@ static inline int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_
 
 static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 {
+	struct user_i387_ia32_struct *envp = NULL;
+	int state_size = fpu_kernel_xstate_size;
 	int ia32_fxstate = (buf != buf_fx);
 	struct task_struct *tsk = current;
 	struct fpu *fpu = &tsk->thread.fpu;
-	int state_size = fpu_kernel_xstate_size;
+	struct user_i387_ia32_struct env;
+	union fpregs_state *state;
 	u64 xfeatures = 0;
 	int fx_only = 0;
+	int ret = 0;
+	void *tmp;
 
 	ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
 			 IS_ENABLED(CONFIG_IA32_EMULATION));
@@ -303,56 +308,24 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 		}
 	}
 
-	if (ia32_fxstate) {
-		/*
-		 * For 32-bit frames with fxstate, copy the user state to the
-		 * thread's fpu state, reconstruct fxstate from the fsave
-		 * header. Validate and sanitize the copied state.
-		 */
-		struct user_i387_ia32_struct env;
-		union fpregs_state *state;
-		int err = 0;
-		void *tmp;
-
 	tmp = kzalloc(sizeof(*state) + fpu_kernel_xstate_size + 64, GFP_KERNEL);
 	if (!tmp)
 		return -ENOMEM;
 	state = PTR_ALIGN(tmp, 64);
 
-		if (using_compacted_format()) {
-			err = copy_user_to_xstate(&state->xsave, buf_fx);
-		} else {
-			err = __copy_from_user(&state->xsave, buf_fx, state_size);
-
-			if (!err && state_size > offsetof(struct xregs_state, header))
-				err = validate_xstate_header(&state->xsave.header);
-		}
-
-		if (err || __copy_from_user(&env, buf, sizeof(env))) {
-			err = -1;
-		} else {
-			sanitize_restored_xstate(state, &env, xfeatures, fx_only);
-			copy_kernel_to_fpregs(state);
-		}
-
-		kfree(tmp);
-		return err;
-	} else {
-		union fpregs_state *state;
-		void *tmp;
-		int ret;
-
-		tmp = kzalloc(sizeof(*state) + fpu_kernel_xstate_size + 64, GFP_KERNEL);
-		if (!tmp)
-			return -ENOMEM;
-		state = PTR_ALIGN(tmp, 64);
+	if ((unsigned long)buf_fx % 64)
+		fx_only = 1;
 
 	/*
-		 * For 64-bit frames and 32-bit fsave frames, restore the user
-		 * state to the registers directly (with exceptions handled).
+	 * For 32-bit frames with fxstate, copy the fxstate so it can be
+	 * reconstructed later.
 	 */
-		if ((unsigned long)buf_fx % 64)
-			fx_only = 1;
+	if (ia32_fxstate) {
+		ret = __copy_from_user(&env, buf, sizeof(env));
+		if (ret)
+			goto err_out;
+		envp = &env;
+	}
 
 	if (use_xsave() && !fx_only) {
 		u64 init_bv = xfeatures_mask & ~xfeatures;
@@ -368,7 +341,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 		if (ret)
 			goto err_out;
 
-			sanitize_restored_xstate(state, NULL, xfeatures, fx_only);
+		sanitize_restored_xstate(state, envp, xfeatures, fx_only);
 
 		if (unlikely(init_bv))
 			copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
@@ -379,11 +352,11 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 		if (ret)
 			goto err_out;
 
+		sanitize_restored_xstate(state, envp, xfeatures, fx_only);
 		if (use_xsave()) {
 			u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE;
 			copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 		}
-			state->fxsave.mxcsr &= mxcsr_feature_mask;
 
 		ret = copy_kernel_to_fxregs_err(&state->fxsave);
 	} else {
@@ -395,13 +368,9 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 
 err_out:
 	kfree(tmp);
-		if (ret) {
+	if (ret)
 		fpu__clear(fpu);
-			return -1;
-		}
-	}
-
-	return 0;
+	return ret;
 }
 
 static inline int xstate_sigframe_size(void)