x86/fpu: Replace KVMs home brewed FPU copy from user

Copying a user space buffer to the memory buffer is already available in
the FPU core. The copy mechanism in KVM lacks sanity checks and needs to
use cpuid() to lookup the offset of each component, while the FPU core has
this information cached.

Make the FPU core variant accessible for KVM and replace the home brewed
mechanism.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: kvm@vger.kernel.org
Link: https://lkml.kernel.org/r/20211015011539.134065207@linutronix.de

2 files changed, 38 insertions, 3 deletions

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 023bfe857907..65fc87760011 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -174,7 +174,43 @@ void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask)
 	fpregs_unlock();
 }
 EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpu);
-#endif
+
+int fpu_copy_kvm_uabi_to_fpstate(struct fpu *fpu, const void *buf, u64 xcr0,
+				 u32 *vpkru)
+{
+	union fpregs_state *kstate = &fpu->state;
+	const union fpregs_state *ustate = buf;
+	struct pkru_state *xpkru;
+	int ret;
+
+	if (!cpu_feature_enabled(X86_FEATURE_XSAVE)) {
+		if (ustate->xsave.header.xfeatures & ~XFEATURE_MASK_FPSSE)
+			return -EINVAL;
+		if (ustate->fxsave.mxcsr & ~mxcsr_feature_mask)
+			return -EINVAL;
+		memcpy(&kstate->fxsave, &ustate->fxsave, sizeof(ustate->fxsave));
+		return 0;
+	}
+
+	if (ustate->xsave.header.xfeatures & ~xcr0)
+		return -EINVAL;
+
+	ret = copy_uabi_from_kernel_to_xstate(&kstate->xsave, ustate);
+	if (ret)
+		return ret;
+
+	/* Retrieve PKRU if not in init state */
+	if (kstate->xsave.header.xfeatures & XFEATURE_MASK_PKRU) {
+		xpkru = get_xsave_addr(&kstate->xsave, XFEATURE_PKRU);
+		*vpkru = xpkru->pkru;
+	}
+
+	/* Ensure that XCOMP_BV is set up for XSAVES */
+	xstate_init_xcomp_bv(&kstate->xsave, xfeatures_mask_uabi());
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fpu_copy_kvm_uabi_to_fpstate);
+#endif /* CONFIG_KVM */
 
 void kernel_fpu_begin_mask(unsigned int kfpu_mask)
 {
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 68355605ca75..eeeb807b9717 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1134,8 +1134,7 @@ static int copy_uabi_to_xstate(struct xregs_state *xsave, const void *kbuf,
 
 /*
  * Convert from a ptrace standard-format kernel buffer to kernel XSAVE[S]
- * format and copy to the target thread. This is called from
- * xstateregs_set().
+ * format and copy to the target thread. Used by ptrace and KVM.
  */
 int copy_uabi_from_kernel_to_xstate(struct xregs_state *xsave, const void *kbuf)
 {