Re: [PATCH] kprobes: Forbid probing on kprobe_insn_slot

[Chen Zhongjin]

Hi,

On 2022/7/31 23:48, Masami Hiramatsu (Google) wrote:
> On Wed, 27 Jul 2022 11:20:58 +0800
> Chen Zhongjin <chenzhongjin@xxxxxxxxxx> wrote:
>
> > Syzkaller reported a BUG on arm64:
> > Unrecoverable kprobe detected.
> > Dumping kprobe:
> > Name: (null)
> > Offset: 0
> > Address: 0xffffa00010019000
> > ------------[ cut here ]------------
> > kernel BUG at arch/arm64/kernel/probes/kprobes.c:235!
> > Internal error: Oops - BUG: 0 [#1] SMP
> > Modules linked in:
> > CPU: 1 PID: 31060 Comm: syz-executor.6 Not tainted 5.10.0 #11
> > ...
> > Call trace:
> >   reenter_kprobe arch/arm64/kernel/probes/kprobes.c:234 [inline]
> >   kprobe_handler+0x23c/0x26c arch/arm64/kernel/probes/kprobes.c:339
> >   kprobe_breakpoint_handler+0x24/0x34 arch/arm64/kernel/probes/kprobes.c:406
> >   call_break_hook+0xf4/0x13c arch/arm64/kernel/debug-monitors.c:322
> >   brk_handler+0x2c/0xa0 arch/arm64/kernel/debug-monitors.c:329
> >   do_debug_exception+0x140/0x230 arch/arm64/mm/fault.c:867
> >   el1_dbg+0x38/0x50 arch/arm64/kernel/entry-common.c:182
> >   el1_sync_handler+0xf4/0x150 arch/arm64/kernel/entry-common.c:219
> >   el1_sync+0x74/0x100 arch/arm64/kernel/entry.S:665
> >   0xffffa00010019000
> >   do_futex+0x2f4/0x370 kernel/futex.c:3735
> >   __do_sys_futex kernel/futex.c:3798 [inline]
> >   __se_sys_futex kernel/futex.c:3764 [inline]
> >   __arm64_sys_futex+0x168/0x3a0 kernel/futex.c:3764
> >   __invoke_syscall arch/arm64/kernel/syscall.c:36 [inline]
> >   invoke_syscall arch/arm64/kernel/syscall.c:48 [inline]
> >   el0_svc_common.constprop.0+0xf4/0x414 arch/arm64/kernel/syscall.c:155
> >   do_el0_svc+0x50/0x11c arch/arm64/kernel/syscall.c:217
> >   el0_svc+0x20/0x30 arch/arm64/kernel/entry-common.c:353
> >   el0_sync_handler+0xe4/0x1e0 arch/arm64/kernel/entry-common.c:369
> >   el0_sync+0x148/0x180 arch/arm64/kernel/entry.S:683
> > Code: 91018360 97ff1838 aa1703e0 97ff1fdf (d4210000)
> > ---[ end trace 767503e946e01b15 ]---
> >
> > Syzbot tried to porbe on a kprobe_insn_slot.
> >
> > kprobe will replace instruciton with a break and store the origin one
> > on kprobe_insn_slot. However these slots are not in .kprobes.text and
> > exported by perf_event_ksymbol so can be probed by perf interface.
> >
> > Probing these slots will triggers kprobe handler inside single step
> > process and for some architectures such as arm64 this will causes a
> > bug().
> >
> > These slots are kprobe process so they should not be probed anyway.
> > Add kprobe_insn_slot check when register_kprobe to forbid probing on
> > these slots.
> Oops, good catch!
>
> Previously this was not counted as text area, but now the kernel_text_address()
> returns true for these trampoline buffers.
>
> In this case, I think kprobes should be limited to probe only
> core_kernel_text and module_text.
> Can you use is_module_text_address() and core_kernel_text() instead?
> Below can allow kprobes probing on other trampolines like ftrace and
> bpf.
> Also, you may need this tag;
>
> Fixes: 5b485629ba0d ("kprobes, extable: Identify kprobes trampolines as kernel text area")
>
> Thank you,

Thanks for review!

Please see next version here: https://lkml.org/lkml/2022/7/31/436

[PATCH v3] kprobes: Forbid probing on trampoline and bpf prog

> > Signed-off-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>
> > ---
> >   kernel/kprobes.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index f214f8c088ed..3e798b62db70 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -1562,6 +1562,8 @@ static int check_kprobe_address_safe(struct kprobe *p,
> >   	/* Ensure it is not in reserved area nor out of text */
> >   	if (!kernel_text_address((unsigned long) p->addr) ||
> >   	    within_kprobe_blacklist((unsigned long) p->addr) ||
> > +	    is_kprobe_insn_slot((unsigned long) p->addr) ||
> > +	    is_kprobe_optinsn_slot((unsigned long) p->addr) ||
> >   	    jump_label_text_reserved(p->addr, p->addr) ||
> >   	    static_call_text_reserved(p->addr, p->addr) ||
> >   	    find_bug((unsigned long)p->addr)) {
> > --
> > 2.17.1
Best,

Chen