[PATCH 1/2] arm64: kprobes: Remove unneeded address sanity check

[Masami Hiramatsu]

Hi David,

On Wed, 14 Feb 2018 21:08:03 -0500
David Long <dave.long at linaro.org> wrote:

> On 02/01/2018 04:34 AM, AKASHI Takahiro wrote:
> > From: Masami Hiramatsu <mhiramat at kernel.org>
> >
> > Remove unneeded address sanity check in arch_prepare_kprobe().
> > Since do_debug_exception() is already blacklisted for kprobes, no need
> > to reject all __exception functions. Also, since generic kprobe
> > framework already ensures the address is in kernel text, no need to
> > check it is in rodata again.
> >
> > Signed-off-by: Masami Hiramatsu <mhiramat at kernel.org>
> > Reported-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
> > ---
> >   arch/arm64/kernel/probes/kprobes.c | 8 --------
> >   1 file changed, 8 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> > index d849d9804011..3c487a389252 100644
> > --- a/arch/arm64/kernel/probes/kprobes.c
> > +++ b/arch/arm64/kernel/probes/kprobes.c
> > @@ -78,8 +78,6 @@ static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
> >   int __kprobes arch_prepare_kprobe(struct kprobe *p)
> >   {
> >   	unsigned long probe_addr = (unsigned long)p->addr;
> > -	extern char __start_rodata[];
> > -	extern char __end_rodata[];
> >
> >   	if (probe_addr & 0x3)
> >   		return -EINVAL;
> > @@ -87,12 +85,6 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
> >   	/* copy instruction */
> >   	p->opcode = le32_to_cpu(*p->addr);
> >
> > -	if (in_exception_text(probe_addr))
> > -		return -EINVAL;
> > -	if (probe_addr >= (unsigned long) __start_rodata &&
> > -	    probe_addr <= (unsigned long) __end_rodata)
> > -		return -EINVAL;
> > -
> >   	/* decode instruction */
> >   	switch (arm_kprobe_decode_insn(p->addr, &p->ainsn)) {
> >   	case INSN_REJECTED:	/* insn not supported */
> >
> 
> I have tested this change on v4.15 using kprobes events and I find it 
> allows kprobes to be placed in exception text when they were previously 
> rejected. Is there some other recent change I need to test this with for 
> the previous behavior to be preserved?

Hmm, the latest change is to avoid retpoline thunk functions on x86. Since the
retpoline may not be applied on aarch64, it can be ignored.
However, I found there were still many "__kprobes" tags under arch/arm64. That
was replaced with NOKPROBE_SYMBOL() (and nokprobe_inline for inline function).
It should be done on arm/arm64 too because the functions marked with
NOKPROBE_SYMBOL are listed in <debugfs>/kprobes/blacklist. 

Thank you,

> 
> -dl
> 


-- 
Masami Hiramatsu <mhiramat at kernel.org>