linux-kernel - [PATCH 3.10 037/139] MIPS: Fix unaligned PC interpretation in `compute_return

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Message-Id: <1509571159-4405-38-git-send-email-w@1wt.eu>
Date:   Wed,  1 Nov 2017 22:17:37 +0100
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     "Maciej W. Rozycki" <macro@...tec.com>,
        James Hogan <james.hogan@...tec.com>,
        linux-mips@...ux-mips.org, Ralf Baechle <ralf@...ux-mips.org>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 037/139] MIPS: Fix unaligned PC interpretation in `compute_return_epc'

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

commit 11a3799dbeb620bf0400b1fda5cc2c6bea55f20a upstream.

Fix a regression introduced with commit fb6883e5809c ("MIPS: microMIPS:
Support handling of delay slots.") and defer to `__compute_return_epc'
if the ISA bit is set in EPC with non-MIPS16, non-microMIPS hardware,
which will then arrange for a SIGBUS due to an unaligned instruction
reference.  Returning EPC here is never correct as the API defines this
function's result to be either a negative error code on failure or one
of 0 and BRANCH_LIKELY_TAKEN on success.

Fixes: fb6883e5809c ("MIPS: microMIPS: Support handling of delay slots.")
Signed-off-by: Maciej W. Rozycki <macro@...tec.com>
Cc: James Hogan <james.hogan@...tec.com>
Cc: linux-mips@...ux-mips.org
Cc: stable@...r.kernel.org 
Patchwork: https://patchwork.linux-mips.org/patch/16395/
Signed-off-by: Ralf Baechle <ralf@...ux-mips.org>
Signed-off-by: Willy Tarreau <w@....eu>
---
 arch/mips/include/asm/branch.h | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/mips/include/asm/branch.h b/arch/mips/include/asm/branch.h
index e28a3e0..582d8b6 100644
--- a/arch/mips/include/asm/branch.h
+++ b/arch/mips/include/asm/branch.h
@@ -44,10 +44,7 @@ static inline int compute_return_epc(struct pt_regs *regs)
 			return __microMIPS_compute_return_epc(regs);
 		if (cpu_has_mips16)
 			return __MIPS16e_compute_return_epc(regs);
-		return regs->cp0_epc;
-	}
-
-	if (!delay_slot(regs)) {
+	} else if (!delay_slot(regs)) {
 		regs->cp0_epc += 4;
 		return 0;
 	}
-- 
2.8.0.rc2.1.gbe9624a