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Rao" To: Michael Ellerman , Steven Rostedt , Masami Hiramatsu , Ingo Molnar , Nicholas Piggin Cc: , Subject: [PATCH 7/7] powerpc/kprobes: Allow probing on any ftrace address Date: Tue, 18 Jun 2019 20:17:06 +0530 X-Mailer: git-send-email 2.22.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 x-cbid: 19061814-0020-0000-0000-0000034B28F5 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19061814-0021-0000-0000-0000219E7782 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-18_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=238 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906180119 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org With KPROBES_ON_FTRACE, kprobe is allowed to be inserted on instructions that branch to _mcount (referred to as ftrace location). With -mprofile-kernel, we now include the preceding 'mflr r0' as being part of the ftrace location. However, by default, probing on an instruction that is not actually the branch to _mcount() is prohibited, as that is considered to not be at an instruction boundary. This is not the case on powerpc, so allow the same by overriding arch_check_ftrace_location() In addition, we update kprobe_ftrace_handler() to detect this scenarios and to pass the proper nip to the pre and post probe handlers. Signed-off-by: Naveen N. Rao --- arch/powerpc/kernel/kprobes-ftrace.c | 30 ++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/arch/powerpc/kernel/kprobes-ftrace.c b/arch/powerpc/kernel/kprobes-ftrace.c index 972cb28174b2..6a0bd3c16cb6 100644 --- a/arch/powerpc/kernel/kprobes-ftrace.c +++ b/arch/powerpc/kernel/kprobes-ftrace.c @@ -12,14 +12,34 @@ #include #include +/* + * With -mprofile-kernel, we patch two instructions -- the branch to _mcount + * as well as the preceding 'mflr r0'. Both these instructions are claimed + * by ftrace and we should allow probing on either instruction. + */ +int arch_check_ftrace_location(struct kprobe *p) +{ + if (ftrace_location((unsigned long)p->addr)) + p->flags |= KPROBE_FLAG_FTRACE; + return 0; +} + /* Ftrace callback handler for kprobes */ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, struct ftrace_ops *ops, struct pt_regs *regs) { struct kprobe *p; + int mflr_kprobe = 0; struct kprobe_ctlblk *kcb; p = get_kprobe((kprobe_opcode_t *)nip); + if (unlikely(!p)) { + p = get_kprobe((kprobe_opcode_t *)(nip - MCOUNT_INSN_SIZE)); + if (!p) + return; + mflr_kprobe = 1; + } + if (unlikely(!p) || kprobe_disabled(p)) return; @@ -33,6 +53,9 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, */ regs->nip -= MCOUNT_INSN_SIZE; + if (mflr_kprobe) + regs->nip -= MCOUNT_INSN_SIZE; + __this_cpu_write(current_kprobe, p); kcb->kprobe_status = KPROBE_HIT_ACTIVE; if (!p->pre_handler || !p->pre_handler(p, regs)) { @@ -45,6 +68,8 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, kcb->kprobe_status = KPROBE_HIT_SSDONE; p->post_handler(p, regs, 0); } + if (mflr_kprobe) + regs->nip += MCOUNT_INSN_SIZE; } /* * If pre_handler returns !0, it changes regs->nip. We have to @@ -57,6 +82,11 @@ NOKPROBE_SYMBOL(kprobe_ftrace_handler); int arch_prepare_kprobe_ftrace(struct kprobe *p) { + if ((unsigned long)p->addr & 0x03) { + printk("Attempt to register kprobe at an unaligned address\n"); + return -EILSEQ; + } + p->ainsn.insn = NULL; p->ainsn.boostable = -1; return 0; -- 2.22.0