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

From: tip-bot2 for Fenghua Yu
Date: Sat May 16 2020 - 11:10:50 EST

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

Commit-ID: b860eb8dce5906b14e3a7f3c771e0b3d6ef61b94
Gitweb: https://git.kernel.org/tip/b860eb8dce5906b14e3a7f3c771e0b3d6ef61b94
Author: Fenghua Yu <fenghua.yu@xxxxxxxxx>
AuthorDate: Tue, 12 May 2020 07:54:39 -07:00
Committer: Borislav Petkov <bp@xxxxxxx>
CommitterDate: Wed, 13 May 2020 13:41:50 +02:00

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@xxxxxxxxx>
Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Link: https://lkml.kernel.org/r/20200512145444.15483-6-yu-cheng.yu@xxxxxxxxx
---
arch/x86/include/asm/fpu/internal.h | 3 +-
arch/x86/kernel/fpu/core.c | 53 ++++++++++++++++++----------
arch/x86/kernel/fpu/signal.c | 4 +-
arch/x86/kernel/process.c | 2 +-
arch/x86/kernel/signal.c | 2 +-
5 files changed, 41 insertions(+), 23 deletions(-)

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index ccb1bb3..a42fcb4 100644
--- 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
--- 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
--- 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
--- 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
--- 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);
}