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

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Message-ID: <162448617630.395.1897834764877302937.tip-bot2@tip-bot2>
Date:   Wed, 23 Jun 2021 22:09:36 -0000
From:   "tip-bot2 for Andy Lutomirski" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...e.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/fpu] x86/fpu: Fail ptrace() requests that try to set
 invalid MXCSR values

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

Commit-ID:     145e9e0d8c6fada4a40f9fc65b34658077874d9c
Gitweb:        https://git.kernel.org/tip/145e9e0d8c6fada4a40f9fc65b34658077874d9c
Author:        Andy Lutomirski <luto@...nel.org>
AuthorDate:    Wed, 23 Jun 2021 14:01:40 +02:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Wed, 23 Jun 2021 17:49:46 +02:00

x86/fpu: Fail ptrace() requests that try to set invalid MXCSR values

There is no benefit from accepting and silently changing an invalid MXCSR
value supplied via ptrace().  Instead, return -EINVAL on invalid input.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Link: https://lkml.kernel.org/r/20210623121452.613614842@linutronix.de
---
 arch/x86/kernel/fpu/regset.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
index f24ce87..5610f77 100644
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -63,8 +63,9 @@ int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
 	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)
+		return -EINVAL;
 
 	fpu__prepare_write(fpu);