linux-kernel - [PATCH 4.9 19/25] ARM: 9197/1: spectre-bhb: fix loop8 sequence for Thumb2

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Date:   Mon, 23 May 2022 19:03:37 +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, Ard Biesheuvel <ardb@...nel.org>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 19/25] ARM: 9197/1: spectre-bhb: fix loop8 sequence for Thumb2

From: Ard Biesheuvel <ardb@...nel.org>

[ Upstream commit 3cfb3019979666bdf33a1010147363cf05e0f17b ]

In Thumb2, 'b . + 4' produces a branch instruction that uses a narrow
encoding, and so it does not jump to the following instruction as
expected. So use W(b) instead.

Fixes: 6c7cb60bff7a ("ARM: fix Thumb2 regression with Spectre BHB")
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/arm/kernel/entry-armv.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 77ec669fd5ee..247229e69322 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -1074,7 +1074,7 @@ vector_bhb_loop8_\name:
 
 	@ bhb workaround
 	mov	r0, #8
-3:	b	. + 4
+3:	W(b)	. + 4
 	subs	r0, r0, #1
 	bne	3b
 	dsb
-- 
2.35.1