Merge: x86/fpu: Keep xfd_state in sync with MSR_IA32_XFD

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/4288

JIRA: https://issues.redhat.com/browse/RHEL-36996  
CVE: CVE-2024-35801  
  
Build Info: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=61392845  
Tested: Successful sanity booted on Intel systems.  
  
commit 10e4b51  
Author: Adamos Ttofari <attofari@amazon.de>  
Date:   Fri Mar 22 16:04:39 2024 -0700  
  
    x86/fpu: Keep xfd_state in sync with MSR_IA32_XFD  
  
    Commit 6723654 ("x86/fpu: Update XFD state where required") and  
    commit 8bf2675 ("x86/fpu: Add XFD state to fpstate") introduced a  
    per CPU variable xfd_state to keep the MSR_IA32_XFD value cached, in  
    order to avoid unnecessary writes to the MSR.  
  
    On CPU hotplug MSR_IA32_XFD is reset to the init_fpstate.xfd, which  
    wipes out any stale state. But the per CPU cached xfd value is not  
    reset, which brings them out of sync.  
  
    As a consequence a subsequent xfd_update_state() might fail to update  
    the MSR which in turn can result in XRSTOR raising a #NM in kernel  
    space, which crashes the kernel.  
  
    To fix this, introduce xfd_set_state() to write xfd_state together  
    with MSR_IA32_XFD, and use it in all places that set MSR_IA32_XFD.  
  
    Fixes: 6723654 ("x86/fpu: Update XFD state where required")  
    Signed-off-by: Adamos Ttofari <attofari@amazon.de>  
    Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>  
    Signed-off-by: Ingo Molnar <mingo@kernel.org>  
    Reviewed-by: Thomas Gleixner <tglx@linutronix.de>  
    Link: https://lore.kernel.org/r/20240322230439.456571-1-chang.seok.bae@intel.com  
  
    Closes: https://lore.kernel.org/lkml/20230511152818.13839-1-attofari@amazon.de  
  
Signed-off-by: Steve Best <sbest@redhat.com>

Approved-by: Tony Camuso <tcamuso@redhat.com>
Approved-by: David Arcari <darcari@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Lucas Zampieri <lzampier@redhat.com>

Author: zampierilucas

arch/x86/kernel/fpu/xstate.c

@@ -178,10 +178,11 @@ void fpu__init_cpu_xstate(void)
 	 * Must happen after CR4 setup and before xsetbv() to allow KVM
 	 * lazy passthrough.  Write independent of the dynamic state static
 	 * key as that does not work on the boot CPU. This also ensures
-	 * that any stale state is wiped out from XFD.
+	 * that any stale state is wiped out from XFD. Reset the per CPU
+	 * xfd cache too.
 	 */
 	if (cpu_feature_enabled(X86_FEATURE_XFD))
-		wrmsrl(MSR_IA32_XFD, init_fpstate.xfd);
+		xfd_set_state(init_fpstate.xfd);
 
 	/*
 	 * XCR_XFEATURE_ENABLED_MASK (aka. XCR0) sets user features

arch/x86/kernel/fpu/xstate.h

@@ -148,20 +148,26 @@ static inline void xfd_validate_state(struct fpstate *fpstate, u64 mask, bool rs
 #endif
 
 #ifdef CONFIG_X86_64
+static inline void xfd_set_state(u64 xfd)
+{
+	wrmsrl(MSR_IA32_XFD, xfd);
+	__this_cpu_write(xfd_state, xfd);
+}
+
 static inline void xfd_update_state(struct fpstate *fpstate)
 {
 	if (fpu_state_size_dynamic()) {
 		u64 xfd = fpstate->xfd;
 
-		if (__this_cpu_read(xfd_state) != xfd) {
-			wrmsrl(MSR_IA32_XFD, xfd);
-			__this_cpu_write(xfd_state, xfd);
-		}
+		if (__this_cpu_read(xfd_state) != xfd)
+			xfd_set_state(xfd);
 	}
 }
 
 extern int __xfd_enable_feature(u64 which, struct fpu_guest *guest_fpu);
 #else
+static inline void xfd_set_state(u64 xfd) { }
+
 static inline void xfd_update_state(struct fpstate *fpstate) { }
 
 static inline int __xfd_enable_feature(u64 which, struct fpu_guest *guest_fpu) {