Message ID | d26f5467577ff0aeecea55e7035ea64e303bdf17.1560868106.git.naveen.n.rao@linux.vnet.ibm.com (mailing list archive) |
---|---|
State | Superseded |
Headers | show |
Series | powerpc/ftrace: Patch out -mprofile-kernel instructions | expand |
Context | Check | Description |
---|---|---|
snowpatch_ozlabs/apply_patch | success | Successfully applied on branch next (e610a466d16a086e321f0bd421e2fc75cff28605) |
snowpatch_ozlabs/build-ppc64le | success | Build succeeded |
snowpatch_ozlabs/build-ppc64be | success | Build succeeded |
snowpatch_ozlabs/build-ppc64e | success | Build succeeded |
snowpatch_ozlabs/build-pmac32 | success | Build succeeded |
snowpatch_ozlabs/checkpatch | warning | total: 0 errors, 1 warnings, 0 checks, 62 lines checked |
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. Thank you, > 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 >
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>
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
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)) { + 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;
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(+)