Re: [PATCH 7/7] powerpc/kprobes: Allow probing on any ftrace address
Masami Hiramatsu wrote:
On Tue, 18 Jun 2019 20:17:06 +0530
"Naveen N. Rao" 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
---
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)) {
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" 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_ or pr_
All good points. Thanks for the review.
- Naveen
Re: [PATCH 7/7] powerpc/kprobes: Allow probing on any ftrace address
On Fri, 2019-06-21 at 23:50 +0900, Masami Hiramatsu wrote:
> On Tue, 18 Jun 2019 20:17:06 +0530
> "Naveen N. Rao" 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_ or pr_
Re: [PATCH 7/7] powerpc/kprobes: Allow probing on any ftrace address
On Tue, 18 Jun 2019 20:17:06 +0530
"Naveen N. Rao" 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
> ---
> 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)) {
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
>
--
Masami Hiramatsu
[PATCH 7/7] powerpc/kprobes: Allow probing on any ftrace address
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
