linux-kernel - [PATCH] powerpc: Avoid link stack corruption in {add_}reloc

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Message-Id: <ad031afa4b884c7dee5cddbdf3093c796fe126eb.1629436491.git.christophe.leroy@csgroup.eu>
Date:   Fri, 20 Aug 2021 05:16:11 +0000 (UTC)
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:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc: Avoid link stack corruption in {add_}reloc_offset

reloc_offset() / add_reloc_offset() used bl;mflr to get code
position.

Use bcl 20,31,+4 instead of bl in order to preserve link stack.

See commit c974809a26a1 ("powerpc/vdso: Avoid link stack corruption
in __get_datapage()") for details.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/misc.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/misc.S b/arch/powerpc/kernel/misc.S
index 5be96feccb55..acd557637a3c 100644
--- a/arch/powerpc/kernel/misc.S
+++ b/arch/powerpc/kernel/misc.S
@@ -29,7 +29,7 @@ _GLOBAL(reloc_offset)
 	li	r3, 0
 _GLOBAL(add_reloc_offset)
 	mflr	r0
-	bl	1f
+	bcl	20,31,1f
 1:	mflr	r5
 	PPC_LL	r4,(2f-1b)(r5)
 	subf	r5,r4,r5
-- 
2.25.0