Commit b860eb8d authored by Fenghua Yu's avatar Fenghua Yu Committed by Borislav Petkov
Browse files

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: default avatarYu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: default avatarFenghua Yu <fenghua.yu@intel.com>
Signed-off-by: default avatarYu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarTony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20200512145444.15483-6-yu-cheng.yu@intel.com
parent 71581eef

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

+2 −1
Original line number Diff line number Diff line
@@ -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);

arch/x86/kernel/fpu/core.c

+35 −18
Original line number Diff line number Diff line
@@ -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);



	if (!static_cpu_has(X86_FEATURE_FPU)) {

		fpu__drop(fpu);



	/*

	 * Make sure fpstate is cleared and initialized.

	 */

		fpu__initialize(fpu);

	if (static_cpu_has(X86_FEATURE_FPU))

		copy_init_fpstate_to_fpregs();

		return;

	}



	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);

}



/*

arch/x86/kernel/fpu/signal.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

}

arch/x86/kernel/process.c

+1 −1
Original line number Diff line number Diff line
@@ -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)

arch/x86/kernel/signal.c

+1 −1
Original line number Diff line number Diff line
@@ -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);

}

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