Messages in this thread | | | Date | Wed, 26 Jun 2019 15:09:56 +0530 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH 7/7] powerpc/kprobes: Allow probing on any ftrace address |
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Masami Hiramatsu wrote: > On Tue, 18 Jun 2019 20:17:06 +0530 > "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote: > >> 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 <naveen.n.rao@linux.vnet.ibm.com> >> --- >> 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 <linux/preempt.h> >> #include <linux/ftrace.h> >> >> +/* >> + * 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)) { > > Hmm, is this really unlikely? If we put a kprobe on the second instruction address, > we will see p == NULL always. > >> + p = get_kprobe((kprobe_opcode_t *)(nip - MCOUNT_INSN_SIZE)); >> + if (!p) > > Here will be unlikely, because we can not find kprobe at both of nip and > nip - MCOUNT_INSN_SIZE. > >> + return; >> + mflr_kprobe = 1; >> + } >> + >> if (unlikely(!p) || kprobe_disabled(p)) > > "unlikely(!p)" is not needed here.
...
Joe Perches wrote: > On Fri, 2019-06-21 at 23:50 +0900, Masami Hiramatsu wrote: >> On Tue, 18 Jun 2019 20:17:06 +0530 >> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote: > > trivia: > >> > diff --git a/arch/powerpc/kernel/kprobes-ftrace.c b/arch/powerpc/kernel/kprobes-ftrace.c > [] >> > @@ -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"); > > Please use the appropriate KERN_<LEVEL> or pr_<level> >
All good points. Thanks for the review.
- Naveen
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