x86/fpu/xstate: Define new functions for clearing fpregs and xstates

Currently, fpu__clear() clears all fpregs and xstates.  Once XSAVES
supervisor states are introduced, supervisor settings (e.g. CET xstates)
must remain active for signals; It is necessary to have separate functions:

- Create fpu__clear_user_states(): clear only user settings for signals;
- Create fpu__clear_all(): clear both user and supervisor settings in
   flush_thread().

Also modify copy_init_fpstate_to_fpregs() to take a mask from above two
functions.

Remove obvious side-comment in fpu__clear(), while at it.

 [ bp: Make the second argument of fpu__clear() bool after requesting it
   a bunch of times during review.
  - Add a comment about copy_init_fpstate_to_fpregs() locking needs. ]

Co-developed-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20200512145444.15483-6-yu-cheng.yu@intel.com

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index ccb1bb3..a42fcb4 100644 (file)
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -31,7 +31,8 @@ extern void fpu__save(struct fpu *fpu);
 extern int  fpu__restore_sig(void __user *buf, int ia32_frame);
 extern void fpu__drop(struct fpu *fpu);
 extern int  fpu__copy(struct task_struct *dst, struct task_struct *src);
-extern void fpu__clear(struct fpu *fpu);
+extern void fpu__clear_user_states(struct fpu *fpu);
+extern void fpu__clear_all(struct fpu *fpu);
 extern int  fpu__exception_code(struct fpu *fpu, int trap_nr);
 extern int  dump_fpu(struct pt_regs *ptregs, struct user_i387_struct *fpstate);
 

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 12c7084..06c8189 100644 (file)
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -291,15 +291,13 @@ void fpu__drop(struct fpu *fpu)
 }
 
 /*
- * Clear FPU registers by setting them up from
- * the init fpstate:
+ * Clear FPU registers by setting them up from the init fpstate.
+ * Caller must do fpregs_[un]lock() around it.
  */
-static inline void copy_init_fpstate_to_fpregs(void)
+static inline void copy_init_fpstate_to_fpregs(u64 features_mask)
 {
-       fpregs_lock();
-
        if (use_xsave())
-               copy_kernel_to_xregs(&init_fpstate.xsave, -1);
+               copy_kernel_to_xregs(&init_fpstate.xsave, features_mask);
        else if (static_cpu_has(X86_FEATURE_FXSR))
                copy_kernel_to_fxregs(&init_fpstate.fxsave);
        else
@@ -307,9 +305,6 @@ static inline void copy_init_fpstate_to_fpregs(void)
 
        if (boot_cpu_has(X86_FEATURE_OSPKE))
                copy_init_pkru_to_fpregs();
-
-       fpregs_mark_activate();
-       fpregs_unlock();
 }
 
 /*
@@ -318,18 +313,40 @@ static inline void copy_init_fpstate_to_fpregs(void)
  * Called by sys_execve(), by the signal handler code and by various
  * error paths.
  */
-void fpu__clear(struct fpu *fpu)
+static void fpu__clear(struct fpu *fpu, bool user_only)
 {
-       WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an anomaly */
+       WARN_ON_FPU(fpu != &current->thread.fpu);
 
-       fpu__drop(fpu);
+       if (!static_cpu_has(X86_FEATURE_FPU)) {
+               fpu__drop(fpu);
+               fpu__initialize(fpu);
+               return;
+       }
 
-       /*
-        * Make sure fpstate is cleared and initialized.
-        */
-       fpu__initialize(fpu);
-       if (static_cpu_has(X86_FEATURE_FPU))
-               copy_init_fpstate_to_fpregs();
+       fpregs_lock();
+
+       if (user_only) {
+               if (!fpregs_state_valid(fpu, smp_processor_id()) &&
+                   xfeatures_mask_supervisor())
+                       copy_kernel_to_xregs(&fpu->state.xsave,
+                                            xfeatures_mask_supervisor());
+               copy_init_fpstate_to_fpregs(xfeatures_mask_user());
+       } else {
+               copy_init_fpstate_to_fpregs(xfeatures_mask_all);
+       }
+
+       fpregs_mark_activate();
+       fpregs_unlock();
+}
+
+void fpu__clear_user_states(struct fpu *fpu)
+{
+       fpu__clear(fpu, true);
+}
+
+void fpu__clear_all(struct fpu *fpu)
+{
+       fpu__clear(fpu, false);
 }
 
 /*

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 3df0cfa..cd6eafb 100644 (file)
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -289,7 +289,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
                         IS_ENABLED(CONFIG_IA32_EMULATION));
 
        if (!buf) {
-               fpu__clear(fpu);
+               fpu__clear_user_states(fpu);
                return 0;
        }
 
@@ -416,7 +416,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 
 err_out:
        if (ret)
-               fpu__clear(fpu);
+               fpu__clear_user_states(fpu);
        return ret;
 }
 

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 9da70b2..de182b8 100644 (file)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -191,7 +191,7 @@ void flush_thread(void)
        flush_ptrace_hw_breakpoint(tsk);
        memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
 
-       fpu__clear(&tsk->thread.fpu);
+       fpu__clear_all(&tsk->thread.fpu);
 }
 
 void disable_TSC(void)

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 83b74fb..0052bbe 100644 (file)
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -732,7 +732,7 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs)
                /*
                 * Ensure the signal handler starts with the new fpu state.
                 */
-               fpu__clear(fpu);
+               fpu__clear_user_states(fpu);
        }
        signal_setup_done(failed, ksig, stepping);
 }