From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-bn3nam01on0105.outbound.protection.outlook.com ([104.47.33.105]:23296 "EHLO NAM01-BN3-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1032098AbeCAP0P (ORCPT ); Thu, 1 Mar 2018 10:26:15 -0500 From: Sasha Levin To: "stable@vger.kernel.org" , "stable-commits@vger.kernel.org" CC: Ravi Bangoria , Michael Ellerman , Sasha Levin Subject: [added to the 4.1 stable tree] powerpc/perf: Dereference BHRB entries safely Date: Thu, 1 Mar 2018 15:23:09 +0000 Message-ID: <20180301152116.1486-68-alexander.levin@microsoft.com> References: <20180301152116.1486-1-alexander.levin@microsoft.com> In-Reply-To: <20180301152116.1486-1-alexander.levin@microsoft.com> Content-Language: en-US Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org List-ID: From: Ravi Bangoria This patch has been added to the 4.1 stable tree. If you have any objections, please let us know. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D [ Upstream commit f41d84dddc66b164ac16acf3f584c276146f1c48 ] It's theoretically possible that branch instructions recorded in BHRB (Branch History Rolling Buffer) entries have already been unmapped before they are processed by the kernel. Hence, trying to dereference such memory location will result in a crash. eg: Unable to handle kernel paging request for data at address 0xd000000019= c41764 Faulting instruction address: 0xc000000000084a14 NIP [c000000000084a14] branch_target+0x4/0x70 LR [c0000000000eb828] record_and_restart+0x568/0x5c0 Call Trace: [c0000000000eb3b4] record_and_restart+0xf4/0x5c0 (unreliable) [c0000000000ec378] perf_event_interrupt+0x298/0x460 [c000000000027964] performance_monitor_exception+0x54/0x70 [c000000000009ba4] performance_monitor_common+0x114/0x120 Fix it by deferefencing the addresses safely. Fixes: 691231846ceb ("powerpc/perf: Fix setting of "to" addresses for BHRB"= ) Cc: stable@vger.kernel.org # v3.10+ Suggested-by: Naveen N. Rao Signed-off-by: Ravi Bangoria Reviewed-by: Naveen N. Rao [mpe: Use probe_kernel_read() which is clearer, tweak change log] Signed-off-by: Michael Ellerman Signed-off-by: Sasha Levin --- arch/powerpc/perf/core-book3s.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3= s.c index d90893b76e7c..8a39319e7868 100644 --- a/arch/powerpc/perf/core-book3s.c +++ b/arch/powerpc/perf/core-book3s.c @@ -401,8 +401,12 @@ static __u64 power_pmu_bhrb_to(u64 addr) int ret; __u64 target; =20 - if (is_kernel_addr(addr)) - return branch_target((unsigned int *)addr); + if (is_kernel_addr(addr)) { + if (probe_kernel_read(&instr, (void *)addr, sizeof(instr))) + return 0; + + return branch_target(&instr); + } =20 /* Userspace: need copy instruction here then translate it */ pagefault_disable(); --=20 2.14.1