linux-kernel - [PATCH] powerpc: Mark .opd section read-only

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Message-Id: <3cd40b682fb6f75bb40947b55ca0bac20cb3f995.1634136222.git.christophe.leroy@csgroup.eu>
Date:   Wed, 13 Oct 2021 16:43:54 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc: Mark .opd section read-only

.opd section contains function descriptors used to locate
functions in the kernel. If someone is able to modify a
function descriptor he will be able to run arbitrary
kernel function instead of another.

To avoid that, move .opd section inside read-only memory.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/vmlinux.lds.S | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 40bdefe9caa7..18e42c74abdd 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -143,6 +143,12 @@ SECTIONS
 	SOFT_MASK_TABLE(8)
 	RESTART_TABLE(8)
 
+	.opd : AT(ADDR(.opd) - LOAD_OFFSET) {
+		__start_opd = .;
+		KEEP(*(.opd))
+		__end_opd = .;
+	}
+
 	. = ALIGN(8);
 	__stf_entry_barrier_fixup : AT(ADDR(__stf_entry_barrier_fixup) - LOAD_OFFSET) {
 		__start___stf_entry_barrier_fixup = .;
@@ -339,12 +345,6 @@ SECTIONS
 		*(.branch_lt)
 	}
 
-	.opd : AT(ADDR(.opd) - LOAD_OFFSET) {
-		__start_opd = .;
-		KEEP(*(.opd))
-		__end_opd = .;
-	}
-
 	. = ALIGN(256);
 	.got : AT(ADDR(.got) - LOAD_OFFSET) {
 		__toc_start = .;
-- 
2.31.1