linux-kernel - [tip:x86/urgent] x86/fpu: Fix invalid FPU ptrace state after execve()

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Message-ID: <tip-b22cbe404a9cc3c7949e380fa1861e31934c8978@git.kernel.org>
Date:   Mon, 21 Nov 2016 02:34:54 -0800
From:   tip-bot for Yu-cheng Yu <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     yu-cheng.yu@...el.com, stable@...r.kernel.org,
        peterz@...radead.org, mingo@...nel.org, ravi.v.shankar@...el.com,
        luto@...nel.org, bp@...e.de, linux-kernel@...r.kernel.org,
        fenghua.yu@...el.com, robert@...llahan.org,
        dave.hansen@...ux.intel.com, hpa@...or.com, tglx@...utronix.de,
        torvalds@...ux-foundation.org
Subject: [tip:x86/urgent] x86/fpu: Fix invalid FPU ptrace state after
 execve()

Commit-ID:  b22cbe404a9cc3c7949e380fa1861e31934c8978
Gitweb:     http://git.kernel.org/tip/b22cbe404a9cc3c7949e380fa1861e31934c8978
Author:     Yu-cheng Yu <yu-cheng.yu@...el.com>
AuthorDate: Thu, 17 Nov 2016 09:11:35 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 21 Nov 2016 10:38:35 +0100

x86/fpu: Fix invalid FPU ptrace state after execve()

Robert O'Callahan reported that after an execve PTRACE_GETREGSET
NT_X86_XSTATE continues to return the pre-exec register values
until the exec'ed task modifies FPU state.

The test code is at:

  https://bugzilla.redhat.com/attachment.cgi?id=1164286.

What is happening is fpu__clear() does not properly clear fpstate.
Fix it by doing just that.

Reported-by: Robert O'Callahan <robert@...llahan.org>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc: <stable@...r.kernel.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...e.de>
Cc: David Hansen <dave.hansen@...ux.intel.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ravi V. Shankar <ravi.v.shankar@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1479402695-6553-1-git-send-email-yu-cheng.yu@intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/fpu/core.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 4700401..ebb4e95 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -521,14 +521,14 @@ void fpu__clear(struct fpu *fpu)
 {
 	WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an anomaly */
 
-	if (!use_eager_fpu() || !static_cpu_has(X86_FEATURE_FPU)) {
-		/* FPU state will be reallocated lazily at the first use. */
-		fpu__drop(fpu);
-	} else {
-		if (!fpu->fpstate_active) {
-			fpu__activate_curr(fpu);
-			user_fpu_begin();
-		}
+	fpu__drop(fpu);
+
+	/*
+	 * Make sure fpstate is cleared and initialized.
+	 */
+	if (static_cpu_has(X86_FEATURE_FPU)) {
+		fpu__activate_curr(fpu);
+		user_fpu_begin();
 		copy_init_fpstate_to_fpregs();
 	}
 }