linux-kernel - [PATCH 5.4 043/135] powerpc/8xx: Fix clearing of bits 20-23 in ITLB miss

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Date:   Thu, 27 Feb 2020 14:36:23 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Christophe Leroy <christophe.leroy@....fr>,
        Leonardo Bras <leonardo@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH 5.4 043/135] powerpc/8xx: Fix clearing of bits 20-23 in ITLB miss

From: Christophe Leroy <christophe.leroy@....fr>

commit a4031afb9d10d97f4d0285844abbc0ab04245304 upstream.

In ITLB miss handled the line supposed to clear bits 20-23 on the L2
ITLB entry is buggy and does indeed nothing, leading to undefined
value which could allow execution when it shouldn't.

Properly do the clearing with the relevant instruction.

Fixes: 74fabcadfd43 ("powerpc/8xx: don't use r12/SPRN_SPRG_SCRATCH2 in TLB Miss handlers")
Cc: stable@...r.kernel.org # v5.0+
Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
Reviewed-by: Leonardo Bras <leonardo@...ux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/4f70c2778163affce8508a210f65d140e84524b4.1581272050.git.christophe.leroy@c-s.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/powerpc/kernel/head_8xx.S |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -289,7 +289,7 @@ InstructionTLBMiss:
 	 * set.  All other Linux PTE bits control the behavior
 	 * of the MMU.
 	 */
-	rlwimi	r10, r10, 0, 0x0f00	/* Clear bits 20-23 */
+	rlwinm	r10, r10, 0, ~0x0f00	/* Clear bits 20-23 */
 	rlwimi	r10, r10, 4, 0x0400	/* Copy _PAGE_EXEC into bit 21 */
 	ori	r10, r10, RPN_PATTERN | 0x200 /* Set 22 and 24-27 */
 	mtspr	SPRN_MI_RPN, r10	/* Update TLB entry */