Masami Hiramatsu wrote:
On Tue, 18 Jun 2019 20:17:06 +0530
"Naveen N. Rao" <naveen.n....@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....@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....@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
