From patchwork Tue Apr 5 07:26:25 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 556997 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 53701C4332F for ; Tue, 5 Apr 2022 11:23:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1359579AbiDELUH (ORCPT ); Tue, 5 Apr 2022 07:20:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52538 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349235AbiDEJt2 (ORCPT ); Tue, 5 Apr 2022 05:49:28 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B9AD31FA68; Tue, 5 Apr 2022 02:42:21 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 6EAA9B81C14; Tue, 5 Apr 2022 09:42:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B66EEC385A2; Tue, 5 Apr 2022 09:42:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649151739; bh=dDEgLEE+d+dNNd5zKLzfFJYE/4qo9BE4nxHk/OiZzKA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jWcw+k9HsX5NlDbXQ0LBbVSm+1G/OePaROxN9msb21I52a0RN9ck+4HkezQOuDpYF PQSk+X0M0YTMn8bmKqnseEiOnAc4YjYL6NRY+bknkrS7r4Pt3iEUuW2lqtV4OMFXXu qqw8gRjhuB/ep5GBj3YlYj+bwO2ZzzQ6+B4Aw7AQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nageswara R Sastry , Michael Ellerman , Nicholas Piggin , Sasha Levin Subject: [PATCH 5.15 523/913] powerpc/64s: Dont use DSISR for SLB faults Date: Tue, 5 Apr 2022 09:26:25 +0200 Message-Id: <20220405070355.529656117@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220405070339.801210740@linuxfoundation.org> References: <20220405070339.801210740@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Michael Ellerman [ Upstream commit d4679ac8ea2e5078704aa1c026db36580cc1bf9a ] Since commit 46ddcb3950a2 ("powerpc/mm: Show if a bad page fault on data is read or write.") we use page_fault_is_write(regs->dsisr) in __bad_page_fault() to determine if the fault is for a read or write, and change the message printed accordingly. But SLB faults, aka Data Segment Interrupts, don't set DSISR (Data Storage Interrupt Status Register) to a useful value. All ISA versions from v2.03 through v3.1 specify that the Data Segment Interrupt sets DSISR "to an undefined value". As far as I can see there's no mention of SLB faults setting DSISR in any BookIV content either. This manifests as accesses that should be a read being incorrectly reported as writes, for example, using the xmon "dump" command: 0:mon> d 0x5deadbeef0000000 5deadbeef0000000 [359526.415354][ C6] BUG: Unable to handle kernel data access on write at 0x5deadbeef0000000 [359526.415611][ C6] Faulting instruction address: 0xc00000000010a300 cpu 0x6: Vector: 380 (Data SLB Access) at [c00000000ffbf400] pc: c00000000010a300: mread+0x90/0x190 If we disassemble the PC, we see a load instruction: 0:mon> di c00000000010a300 c00000000010a300 89490000 lbz r10,0(r9) We can also see in exceptions-64s.S that the data_access_slb block doesn't set IDSISR=1, which means it doesn't load DSISR into pt_regs. So the value we're using to determine if the fault is a read/write is some stale value in pt_regs from a previous page fault. Rework the printing logic to separate the SLB fault case out, and only print read/write in the cases where we can determine it. The result looks like eg: 0:mon> d 0x5deadbeef0000000 5deadbeef0000000 [ 721.779525][ C6] BUG: Unable to handle kernel data access at 0x5deadbeef0000000 [ 721.779697][ C6] Faulting instruction address: 0xc00000000014cbe0 cpu 0x6: Vector: 380 (Data SLB Access) at [c00000000ffbf390] 0:mon> d 0 0000000000000000 [ 742.793242][ C6] BUG: Kernel NULL pointer dereference at 0x00000000 [ 742.793316][ C6] Faulting instruction address: 0xc00000000014cbe0 cpu 0x6: Vector: 380 (Data SLB Access) at [c00000000ffbf390] Fixes: 46ddcb3950a2 ("powerpc/mm: Show if a bad page fault on data is read or write.") Reported-by: Nageswara R Sastry Signed-off-by: Michael Ellerman Reviewed-by: Nicholas Piggin Link: https://lore.kernel.org/r/20220222113449.319193-1-mpe@ellerman.id.au Signed-off-by: Sasha Levin --- arch/powerpc/mm/fault.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c index a8d0ce85d39a..4a15172dfef2 100644 --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -568,18 +568,24 @@ NOKPROBE_SYMBOL(hash__do_page_fault); static void __bad_page_fault(struct pt_regs *regs, int sig) { int is_write = page_fault_is_write(regs->dsisr); + const char *msg; /* kernel has accessed a bad area */ + if (regs->dar < PAGE_SIZE) + msg = "Kernel NULL pointer dereference"; + else + msg = "Unable to handle kernel data access"; + switch (TRAP(regs)) { case INTERRUPT_DATA_STORAGE: - case INTERRUPT_DATA_SEGMENT: case INTERRUPT_H_DATA_STORAGE: - pr_alert("BUG: %s on %s at 0x%08lx\n", - regs->dar < PAGE_SIZE ? "Kernel NULL pointer dereference" : - "Unable to handle kernel data access", + pr_alert("BUG: %s on %s at 0x%08lx\n", msg, is_write ? "write" : "read", regs->dar); break; + case INTERRUPT_DATA_SEGMENT: + pr_alert("BUG: %s at 0x%08lx\n", msg, regs->dar); + break; case INTERRUPT_INST_STORAGE: case INTERRUPT_INST_SEGMENT: pr_alert("BUG: Unable to handle kernel instruction fetch%s",