linux-kernel - [PATCH 3.16 04/86] MIPS: jump_label.c: Correct the span of the J instruction

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Date:   Thu, 16 May 2019 16:55:32 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Ralf Baechle" <ralf@...ux-mips.org>, linux-mips@...ux-mips.org,
        "Maciej W. Rozycki" <macro@...esourcery.com>
Subject: [PATCH 3.16 04/86] MIPS: jump_label.c: Correct the span of the J
 instruction

3.16.68-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: "Maciej W. Rozycki" <macro@...esourcery.com>

commit 99436f7d69045800ffd1d66912f85d37150c7e2b upstream.

Correct the check for the span of the 256MB segment addressable by the J
instruction according to this instruction's semantics.  The calculation
of the jump target is applied to the address of the delay-slot
instruction that immediately follows.  Adjust the check accordingly by
adding 4 to `e->code' that holds the address of the J instruction
itself.

Signed-off-by: Maciej W. Rozycki <macro@...esourcery.com>
Cc: linux-mips@...ux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8515/
Signed-off-by: Ralf Baechle <ralf@...ux-mips.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/mips/kernel/jump_label.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/mips/kernel/jump_label.c
+++ b/arch/mips/kernel/jump_label.c
@@ -27,8 +27,8 @@ void arch_jump_label_transform(struct ju
 	union mips_instruction *insn_p =
 		(union mips_instruction *)(unsigned long)e->code;
 
-	/* Jump only works within a 256MB aligned region. */
-	BUG_ON((e->target & ~J_RANGE_MASK) != (e->code & ~J_RANGE_MASK));
+	/* Jump only works within a 256MB aligned region of its delay slot. */
+	BUG_ON((e->target & ~J_RANGE_MASK) != ((e->code + 4) & ~J_RANGE_MASK));
 
 	/* Target must have 4 byte alignment. */
 	BUG_ON((e->target & 3) != 0);