linux-kernel - [PATCH 5.14 062/151] x86/fpu: Mask out the invalid MXCSR bits properly

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Date:   Mon, 18 Oct 2021 15:24:01 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Borislav Petkov <bp@...e.de>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>, Ser Olmy <ser.olmy@...tonmail.com>
Subject: [PATCH 5.14 062/151] x86/fpu: Mask out the invalid MXCSR bits properly

From: Borislav Petkov <bp@...e.de>

commit b2381acd3fd9bacd2c63f53b2c610c89959b31cc upstream.

This is a fix for the fix (yeah, /facepalm).

The correct mask to use is not the negation of the MXCSR_MASK but the
actual mask which contains the supported bits in the MXCSR register.

Reported and debugged by Ville Syrjälä <ville.syrjala@...ux.intel.com>

Fixes: d298b03506d3 ("x86/fpu: Restore the masking out of reserved MXCSR bits")
Signed-off-by: Borislav Petkov <bp@...e.de>
Tested-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
Tested-by: Ser Olmy <ser.olmy@...tonmail.com>
Cc: <stable@...r.kernel.org>
Link: https://lore.kernel.org/r/YWgYIYXLriayyezv@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kernel/fpu/signal.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -385,7 +385,7 @@ static int __fpu_restore_sig(void __user
 				return -EINVAL;
 		} else {
 			/* Mask invalid bits out for historical reasons (broken hardware). */
-			fpu->state.fxsave.mxcsr &= ~mxcsr_feature_mask;
+			fpu->state.fxsave.mxcsr &= mxcsr_feature_mask;
 		}
 
 		/* Enforce XFEATURE_MASK_FPSSE when XSAVE is enabled */