From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752998AbdJKJCB (ORCPT ); Wed, 11 Oct 2017 05:02:01 -0400 Received: from 20pmail.ess.barracuda.com ([64.235.150.247]:37928 "EHLO 20pmail.ess.barracuda.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752011AbdJKJB4 (ORCPT ); Wed, 11 Oct 2017 05:01:56 -0400 X-Greylist: delayed 169367 seconds by postgrey-1.27 at vger.kernel.org; Wed, 11 Oct 2017 05:01:55 EDT From: Matt Redfearn To: Ralf Baechle , James Hogan CC: Matthew Fortune , , Matt Redfearn , Corey Minyard , , "Jason A. Donenfeld" , Paul Burton Subject: [PATCH] MIPS: Fix exception entry when CONFIG_EVA enabled Date: Wed, 11 Oct 2017 09:59:20 +0100 Message-ID: <1507712360-20657-1-git-send-email-matt.redfearn@mips.com> X-Mailer: git-send-email 2.7.4 MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.150.130.83] X-BESS-ID: 1507712412-298552-31552-21987-10 X-BESS-VER: 2017.12-r1710102214 X-BESS-Apparent-Source-IP: 12.201.5.28 X-BESS-Outbound-Spam-Score: 0.00 X-BESS-Outbound-Spam-Report: Code version 3.2, rules version 3.2.2.185885 Rule breakdown below pts rule name description ---- ---------------------- -------------------------------- 0.00 BSF_BESS_OUTBOUND META: BESS Outbound X-BESS-Outbound-Spam-Status: SCORE=0.00 using account:ESS59374 scores of KILL_LEVEL=7.0 tests=BSF_BESS_OUTBOUND X-BESS-BRTS-Status: 1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit 9fef68686317b ("MIPS: Make SAVE_SOME more standard") made several changes to the order in which registers are saved in the SAVE_SOME macro, used by exception handlers to save the processor state. In particular, it removed the move k1, sp in the delay slot of the branch testing if the processor is already in kernel mode. This is replaced later in the macro by a move k0, sp When CONFIG_EVA is disabled, this instruction actually appears in the delay slot of the branch. However, when CONFIG_EVA is enabled, instead the RPS workaround of MFC0 k0, CP0_ENTRYHI appears in the delay slot. This results in k0 not containing the stack pointer, but some unrelated value, which is then saved to the kernel stack. On exit from the exception, this bogus value is restored to the stack pointer, resulting in an OOPS. Fix this by moving the save of SP in k0 explicitly in the delay slot of the branch, outside of the CONFIG_EVA section, restoring the expected instruction ordering when CONFIG_EVA is active. Fixes: 9fef68686317b ("MIPS: Make SAVE_SOME more standard") Signed-off-by: Matt Redfearn Reported-by: Vladimir Kondratiev --- Note that some of our compiler people are dubious about putting frame related instructions in conditionally executed blocks of code. In this case, presuming that we only care about unwinding the kernel stack, then we only care about the case in which the branch is taken, and k0 always contains the SP to be saved. There is also a question about putting frame related instructions in branch delay slots. Again, in this case, we think it's OK to use them since the only path that ought to be unwound will be the "branch taken" route where we are already on the kernel stack. Not having access to a CFI based kernel stack unwinder makes this change difficult to verify, but since the same construct already existed when CONFIG_EVA is disabled, I don't think this change is likely to break the unwinder, and fixes exception entry when CONFIG_EVA is enabled. Thanks, Matt --- arch/mips/include/asm/stackframe.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/mips/include/asm/stackframe.h b/arch/mips/include/asm/stackframe.h index 5d3563c55e0c..2161357cc68f 100644 --- a/arch/mips/include/asm/stackframe.h +++ b/arch/mips/include/asm/stackframe.h @@ -199,6 +199,10 @@ sll k0, 3 /* extract cu0 bit */ .set noreorder bltz k0, 8f + move k0, sp + .if \docfi + .cfi_register sp, k0 + .endif #ifdef CONFIG_EVA /* * Flush interAptiv's Return Prediction Stack (RPS) by writing @@ -225,10 +229,6 @@ MTC0 k0, CP0_ENTRYHI #endif .set reorder - move k0, sp - .if \docfi - .cfi_register sp, k0 - .endif /* Called from user mode, new stack. */ get_saved_sp docfi=\docfi tosp=1 8: -- 2.7.4