linux-kernel - [patch V2 12/52] x86/fpu: Fail ptrace() requests that try to set invalid MXCSR values

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Date:   Mon, 14 Jun 2021 17:44:20 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: [patch V2 12/52] x86/fpu: Fail ptrace() requests that try to set
 invalid MXCSR values

From: Andy Lutomirski <luto@...nel.org>

We're not doing anyone any favors by accepting and silently changing an
invalid MXCSR value supplied via ptrace().  Instead, return -EINVAL on
invalid input.

If this breaks something, we can revert it.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
V2: New patch. Picked up from Andy.
---
 arch/x86/kernel/fpu/regset.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -65,8 +65,9 @@ int xfpregs_set(struct task_struct *targ
 	if (ret)
 		return ret;
 
-	/* Mask invalid MXCSR bits (for historical reasons). */
-	newstate.mxcsr &= mxcsr_feature_mask;
+	/* Do not allow an invalid MXCSR value. */
+	if (newstate.mxcsr & ~mxcsr_feature_mask)
+		ret = -EINVAL;
 
 	fpu__prepare_write(fpu);