Re: [PATCH 7/7] powerpc/kprobes: Allow probing on any ftrace address
From: Masami Hiramatsu <mhiramat@kernel.org>
Date: 2019-06-21 14:50:41
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On Tue, 18 Jun 2019 20:17:06 +0530 "Naveen N. Rao" [off-list ref] wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- 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,
quoted hunk ↗ jump to hunk
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 [off-list ref]