linux-kernel - [tip:x86/urgent] x86/fpu: Update kernel's FPU state before using for the fsave header

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Date:   Sat, 8 Jun 2019 02:49:14 -0700
From:   tip-bot for Sebastian Andrzej Siewior <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     mingo@...nel.org, bigeasy@...utronix.de, riel@...riel.com,
        tglx@...utronix.de, dave.hansen@...el.com, rkrcmar@...hat.com,
        Jason@...c4.com, ebiggers@...nel.org, luto@...nel.org,
        hughd@...gle.com, kvm@...r.kernel.org, mingo@...hat.com,
        bp@...e.de, x86@...nel.org, hpa@...or.com, jannh@...gle.com,
        pbonzini@...hat.com, linux-kernel@...r.kernel.org
Subject: [tip:x86/urgent] x86/fpu: Update kernel's FPU state before using
 for the fsave header

Commit-ID:  aab8445c4e1cceeb3f739352041ec1c2586bc923
Gitweb:     https://git.kernel.org/tip/aab8445c4e1cceeb3f739352041ec1c2586bc923
Author:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
AuthorDate: Fri, 7 Jun 2019 16:29:16 +0200
Committer:  Borislav Petkov <bp@...e.de>
CommitDate: Sat, 8 Jun 2019 11:45:15 +0200

x86/fpu: Update kernel's FPU state before using for the fsave header

In commit

  39388e80f9b0c ("x86/fpu: Don't save fxregs for ia32 frames in copy_fpstate_to_sigframe()")

I removed the statement

|       if (ia32_fxstate)
|               copy_fxregs_to_kernel(fpu);

and argued that it was wrongly merged because the content was already
saved in kernel's state.

This was wrong: It is required to write it back because it is only
saved on the user-stack and save_fsave_header() reads it from task's
FPU-state. I missed that part…

Save x87 FPU state unless thread's FPU registers are already up to date.

Fixes: 39388e80f9b0c ("x86/fpu: Don't save fxregs for ia32 frames in copy_fpstate_to_sigframe()")
Reported-by: Eric Biggers <ebiggers@...nel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Tested-by: Eric Biggers <ebiggers@...nel.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Jann Horn <jannh@...gle.com>
Cc: "Jason A. Donenfeld" <Jason@...c4.com>
Cc: kvm ML <kvm@...r.kernel.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Rik van Riel <riel@...riel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: x86-ml <x86@...nel.org>
Link: https://lkml.kernel.org/r/20190607142915.y52mfmgk5lvhll7n@linutronix.de
---
 arch/x86/kernel/fpu/signal.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 060d6188b453..0071b794ed19 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -62,6 +62,11 @@ static inline int save_fsave_header(struct task_struct *tsk, void __user *buf)
 		struct user_i387_ia32_struct env;
 		struct _fpstate_32 __user *fp = buf;
 
+		fpregs_lock();
+		if (!test_thread_flag(TIF_NEED_FPU_LOAD))
+			copy_fxregs_to_kernel(&tsk->thread.fpu);
+		fpregs_unlock();
+
 		convert_from_fxsr(&env, tsk);
 
 		if (__copy_to_user(buf, &env, sizeof(env)) ||