[tip: x86/fpu] x86/fpu: Add XFD state to fpstate

[tip-bot2 for Chang S. Bae]

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     8bf26758ca9659866b844dd51037314b4c0fa6bd
Gitweb:        https://git.kernel.org/tip/8bf26758ca9659866b844dd51037314b4c0fa6bd
Author:        Chang S. Bae <chang.seok.bae@xxxxxxxxx>
AuthorDate:    Thu, 21 Oct 2021 15:55:18 -07:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Tue, 26 Oct 2021 10:18:09 +02:00

x86/fpu: Add XFD state to fpstate

Add storage for XFD register state to struct fpstate. This will be used to
store the XFD MSR state. This will be used for switching the XFD MSR when
FPU content is restored.

Add a per-CPU variable to cache the current MSR value so the MSR has only
to be written when the values are different.

Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lkml.kernel.org/r/20211021225527.10184-15-chang.seok.bae@xxxxxxxxx
---
 arch/x86/include/asm/fpu/types.h | 3 +++
 arch/x86/kernel/fpu/core.c       | 2 ++
 arch/x86/kernel/fpu/xstate.h     | 4 ++++
 3 files changed, 9 insertions(+)

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index 595122f..b189763 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -322,6 +322,9 @@ struct fpstate {
 	/* @user_xfeatures:	xfeatures valid in UABI buffers */
 	u64			user_xfeatures;
 
+	/* @xfd:		xfeatures disabled to trap userspace use. */
+	u64			xfd;
+
 	/* @is_valloc:		Indicator for dynamically allocated state */
 	unsigned int		is_valloc	: 1;
 
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 3349068..3b72cdd 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -27,6 +27,7 @@
 
 #ifdef CONFIG_X86_64
 DEFINE_STATIC_KEY_FALSE(__fpu_state_size_dynamic);
+DEFINE_PER_CPU(u64, xfd_state);
 #endif
 
 /* The FPU state configuration data for kernel and user space */
@@ -409,6 +410,7 @@ static void __fpstate_reset(struct fpstate *fpstate)
 	fpstate->user_size	= fpu_user_cfg.default_size;
 	fpstate->xfeatures	= fpu_kernel_cfg.default_features;
 	fpstate->user_xfeatures	= fpu_user_cfg.default_features;
+	fpstate->xfd		= init_fpstate.xfd;
 }
 
 void fpstate_reset(struct fpu *fpu)
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 4ce1dc0..32a4dee 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -5,6 +5,10 @@
 #include <asm/cpufeature.h>
 #include <asm/fpu/xstate.h>
 
+#ifdef CONFIG_X86_64
+DECLARE_PER_CPU(u64, xfd_state);
+#endif
+
 static inline void xstate_init_xcomp_bv(struct xregs_state *xsave, u64 mask)
 {
 	/*