x86/fpu: Add size and mask information to fpstate

Add state size and feature mask information to the fpstate container. This
will be used for runtime checks with the upcoming support for dynamically
enabled features and dynamically sized buffers. That avoids conditionals
all over the place as the required information is accessible for both
default and extended buffers.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145322.921388806@linutronix.de

arch/x86/include/asm/fpu/types.h

@@ -310,6 +310,18 @@ union fpregs_state {
 };
 
 struct fpstate {
+	/* @kernel_size: The size of the kernel register image */
+	unsigned int		size;
+
+	/* @user_size: The size in non-compacted UABI format */
+	unsigned int		user_size;
+
+	/* @xfeatures:		xfeatures for which the storage is sized */
+	u64			xfeatures;
+
+	/* @user_xfeatures:	xfeatures valid in UABI buffers */
+	u64			user_xfeatures;
+
 	/* @regs: The register state union for all supported formats */
 	union fpregs_state		regs;
 

arch/x86/kernel/fpu/core.c

@@ -342,6 +342,12 @@ void fpstate_reset(struct fpu *fpu)
 {
 	/* Set the fpstate pointer to the default fpstate */
 	fpu->fpstate = &fpu->__fpstate;
+
+	/* Initialize sizes and feature masks */
+	fpu->fpstate->size		= fpu_kernel_xstate_size;
+	fpu->fpstate->user_size		= fpu_user_xstate_size;
+	fpu->fpstate->xfeatures		= xfeatures_mask_all;
+	fpu->fpstate->user_xfeatures	= xfeatures_mask_uabi();
 }
 
 #if IS_ENABLED(CONFIG_KVM)

arch/x86/kernel/fpu/init.c

@@ -212,6 +212,14 @@ static void __init fpu__init_system_xstate_size_legacy(void)
 	}
 
 	fpu_user_xstate_size = fpu_kernel_xstate_size;
+	fpstate_reset(&current->thread.fpu);
+}
+
+static void __init fpu__init_init_fpstate(void)
+{
+	/* Bring init_fpstate size and features up to date */
+	init_fpstate.size		= fpu_kernel_xstate_size;
+	init_fpstate.xfeatures		= xfeatures_mask_all;
 }
 
 /*
@@ -233,4 +241,5 @@ void __init fpu__init_system(struct cpuinfo_x86 *c)
 	fpu__init_system_xstate_size_legacy();
 	fpu__init_system_xstate();
 	fpu__init_task_struct_size();
+	fpu__init_init_fpstate();
 }

arch/x86/kernel/fpu/xstate.c

@@ -720,6 +720,7 @@ static void __init fpu__init_disable_system_xstate(void)
 	xfeatures_mask_all = 0;
 	cr4_clear_bits(X86_CR4_OSXSAVE);
 	setup_clear_cpu_cap(X86_FEATURE_XSAVE);
+	fpstate_reset(&current->thread.fpu);
 }
 
 /*
@@ -792,6 +793,8 @@ void __init fpu__init_system_xstate(void)
 	if (err)
 		goto out_disable;
 
+	fpstate_reset(&current->thread.fpu);
+
 	/*
 	 * Update info used for ptrace frames; use standard-format size and no
 	 * supervisor xstates: