From nobody Sun Oct 19 06:10:12 2025 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 D5D81C4332F for ; Wed, 19 Oct 2022 09:18:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233183AbiJSJSK (ORCPT ); Wed, 19 Oct 2022 05:18:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40238 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233723AbiJSJPr (ORCPT ); Wed, 19 Oct 2022 05:15:47 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8C703D0192; Wed, 19 Oct 2022 02:06:30 -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 dfw.source.kernel.org (Postfix) with ESMTPS id E54086186A; Wed, 19 Oct 2022 09:05:51 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id ECD5AC433D7; Wed, 19 Oct 2022 09:05:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666170351; bh=YSgRrx6e5C9KaV05ykt6gXCGLEwA9I+qydBcSRY1t0Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=du0mcH1CETpgxxiPFA5MGeVq0Wz+74fJO+0muw6dQJ+CMXWKa+ScvSdGG4D8h/k9e LSIRrITK7OmXDLDEXlz7/r8ha+2Dtr8QitFkfT/fKhKfuYBV0mD+gVEuNmGADVpwlJ a07YbM5gaxKq1rhZZDie7xJAf+1OLN7b2ajA2/4A= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Li Huafei , Michael Ellerman , Sasha Levin Subject: [PATCH 6.0 622/862] powerpc/kprobes: Fix null pointer reference in arch_prepare_kprobe() Date: Wed, 19 Oct 2022 10:31:49 +0200 Message-Id: <20221019083317.425875660@linuxfoundation.org> X-Mailer: git-send-email 2.38.0 In-Reply-To: <20221019083249.951566199@linuxfoundation.org> References: <20221019083249.951566199@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Li Huafei [ Upstream commit 97f88a3d723162781d6cbfdc7b9617eefab55b19 ] I found a null pointer reference in arch_prepare_kprobe(): # echo 'p cmdline_proc_show' > kprobe_events # echo 'p cmdline_proc_show+16' >> kprobe_events Kernel attempted to read user page (0) - exploit attempt? (uid: 0) BUG: Kernel NULL pointer dereference on read at 0x00000000 Faulting instruction address: 0xc000000000050bfc Oops: Kernel access of bad area, sig: 11 [#1] LE PAGE_SIZE=3D64K MMU=3DRadix SMP NR_CPUS=3D2048 NUMA PowerNV Modules linked in: CPU: 0 PID: 122 Comm: sh Not tainted 6.0.0-rc3-00007-gdcf8e5633e2e #10 NIP: c000000000050bfc LR: c000000000050bec CTR: 0000000000005bdc REGS: c0000000348475b0 TRAP: 0300 Not tainted (6.0.0-rc3-00007-gdcf8e5= 633e2e) MSR: 9000000000009033 CR: 88002444 XER: 2004= 0006 CFAR: c00000000022d100 DAR: 0000000000000000 DSISR: 40000000 IRQMASK: 0 ... NIP arch_prepare_kprobe+0x10c/0x2d0 LR arch_prepare_kprobe+0xfc/0x2d0 Call Trace: 0xc0000000012f77a0 (unreliable) register_kprobe+0x3c0/0x7a0 __register_trace_kprobe+0x140/0x1a0 __trace_kprobe_create+0x794/0x1040 trace_probe_create+0xc4/0xe0 create_or_delete_trace_kprobe+0x2c/0x80 trace_parse_run_command+0xf0/0x210 probes_write+0x20/0x40 vfs_write+0xfc/0x450 ksys_write+0x84/0x140 system_call_exception+0x17c/0x3a0 system_call_vectored_common+0xe8/0x278 --- interrupt: 3000 at 0x7fffa5682de0 NIP: 00007fffa5682de0 LR: 0000000000000000 CTR: 0000000000000000 REGS: c000000034847e80 TRAP: 3000 Not tainted (6.0.0-rc3-00007-gdcf8e5= 633e2e) MSR: 900000000280f033 CR: 44002= 408 XER: 00000000 The address being probed has some special: cmdline_proc_show: Probe based on ftrace cmdline_proc_show+16: Probe for the next instruction at the ftrace locati= on The ftrace-based kprobe does not generate kprobe::ainsn::insn, it gets set to NULL. In arch_prepare_kprobe() it will check for: ... prev =3D get_kprobe(p->addr - 1); preempt_enable_no_resched(); if (prev && ppc_inst_prefixed(ppc_inst_read(prev->ainsn.insn))) { ... If prev is based on ftrace, 'ppc_inst_read(prev->ainsn.insn)' will occur with a null pointer reference. At this point prev->addr will not be a prefixed instruction, so the check can be skipped. Check if prev is ftrace-based kprobe before reading 'prev->ainsn.insn' to fix this problem. Fixes: b4657f7650ba ("powerpc/kprobes: Don't allow breakpoints on suffixes") Signed-off-by: Li Huafei [mpe: Trim oops] Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20220923093253.177298-1-lihuafei1@huawei.com Signed-off-by: Sasha Levin --- arch/powerpc/kernel/kprobes.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c index 912d4f8a13be..bd7b1a035459 100644 --- a/arch/powerpc/kernel/kprobes.c +++ b/arch/powerpc/kernel/kprobes.c @@ -161,7 +161,13 @@ int arch_prepare_kprobe(struct kprobe *p) preempt_disable(); prev =3D get_kprobe(p->addr - 1); preempt_enable_no_resched(); - if (prev && ppc_inst_prefixed(ppc_inst_read(prev->ainsn.insn))) { + + /* + * When prev is a ftrace-based kprobe, we don't have an insn, and it + * doesn't probe for prefixed instruction. + */ + if (prev && !kprobe_ftrace(prev) && + ppc_inst_prefixed(ppc_inst_read(prev->ainsn.insn))) { printk("Cannot register a kprobe on the second word of prefixed instruct= ion\n"); ret =3D -EINVAL; } --=20 2.35.1