Re: [PATCH v2 4/4] kprobes: Remove core dependency on modules

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Thu Apr 4, 2024 at 11:15 AM EEST, Jarkko Sakkinen wrote:
> On Wed Apr 3, 2024 at 6:01 PM EEST, Mark Rutland wrote:
> > From: Jarkko Sakkinen <jarkko@kernel.org>
> >
> > Tracing with kprobes while running a monolithic kernel is currently
> > impossible because KPROBES depends on MODULES. While this dependency is
> > necessary when HAVE_KPROBES_ALLOC=n and the core kprobes code allocates
> > memory using module_alloc(), all the other module-specific code only
> > exist to handle the case when MODULES=y, and can be hidden behind
> > ifdeffery.
> >
> > Add the necessary ifdeffery, and remove the dependency on MODULES=y when
> > HAVE_KPROBES_ALLOC=y.
> >
> > As of this patch kprobes can be used when MODULES=n on arm64 and
> > riscv. All other architectures still depend on MODULES, either by virtue
> > of the core dependency on MODULES when HAVE_KPROBES_ALLOC=n, or by
> > virtue of an explciit dependency on MODULES in arch code.
> >
> > Other architectures can enable support by implementing their own
> > kprobes_alloc_insn_page() and kprobes_free_insn_page() which do not
> > depend on MODULES.
> >
> > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> > Link: https://lore.kernel.org/lkml/20240326134616.7691-1-jarkko@kernel.org/
> > [Mark: Remove execmem changes, depend on HAVE_KPROBES_ALLOC]
> > Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> > Cc: Albert Ou <aou@eecs.berkeley.edu>
> > Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: David S. Miller <davem@davemloft.net>
> > Cc: Jarkko Sakkinen <jarkko@kernel.org>
> > Cc: Masami Hiramatsu <mhiramat@kernel.org>
> > Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com>
> > Cc: Palmer Dabbelt <palmer@dabbelt.com>
> > Cc: Paul Walmsley <paul.walmsley@sifive.com>
> > Cc: Will Deacon <will@kernel.org>
> > ---
> >  arch/Kconfig                |  2 +-
> >  kernel/kprobes.c            | 46 ++++++++++++++++++++++---------------
> >  kernel/trace/trace_kprobe.c | 15 ++++++++++--
> >  3 files changed, 41 insertions(+), 22 deletions(-)
> >
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 85bb59f7b8c07..0df2c88547b3c 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -52,7 +52,7 @@ config GENERIC_ENTRY
> >  
> >  config KPROBES
> >  	bool "Kprobes"
> > -	depends on MODULES
> > +	depends on MODULES || HAVE_KPROBES_ALLOC
> >  	depends on HAVE_KPROBES
> >  	select KALLSYMS
> >  	select TASKS_RCU if PREEMPTION
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index fa2ee4e59eca2..ec4493a41b505 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -1594,6 +1594,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
> >  			goto out;
> >  		}
> >  
> > +#ifdef CONFIG_MODULES
> >  		/*
> >  		 * If the module freed '.init.text', we couldn't insert
> >  		 * kprobes in there.
> > @@ -1604,7 +1605,9 @@ static int check_kprobe_address_safe(struct kprobe *p,
> >  			*probed_mod = NULL;
> >  			ret = -ENOENT;
> >  		}
> > +#endif /* CONFIG_MODULES */
> >  	}
> > +
> >  out:
> >  	preempt_enable();
> >  	jump_label_unlock();
> > @@ -2484,24 +2487,6 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
> >  	return 0;
> >  }
> >  
> > -/* Remove all symbols in given area from kprobe blacklist */
> > -static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
> > -{
> > -	struct kprobe_blacklist_entry *ent, *n;
> > -
> > -	list_for_each_entry_safe(ent, n, &kprobe_blacklist, list) {
> > -		if (ent->start_addr < start || ent->start_addr >= end)
> > -			continue;
> > -		list_del(&ent->list);
> > -		kfree(ent);
> > -	}
> > -}
> > -
> > -static void kprobe_remove_ksym_blacklist(unsigned long entry)
> > -{
> > -	kprobe_remove_area_blacklist(entry, entry + 1);
> > -}
> > -
> >  int __weak arch_kprobe_get_kallsym(unsigned int *symnum, unsigned long *value,
> >  				   char *type, char *sym)
> >  {
> > @@ -2566,6 +2551,25 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
> >  	return ret ? : arch_populate_kprobe_blacklist();
> >  }
> >  
> > +#ifdef CONFIG_MODULES
> > +/* Remove all symbols in given area from kprobe blacklist */
> > +static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
> > +{
> > +	struct kprobe_blacklist_entry *ent, *n;
> > +
> > +	list_for_each_entry_safe(ent, n, &kprobe_blacklist, list) {
> > +		if (ent->start_addr < start || ent->start_addr >= end)
> > +			continue;
> > +		list_del(&ent->list);
> > +		kfree(ent);
> > +	}
> > +}
> > +
> > +static void kprobe_remove_ksym_blacklist(unsigned long entry)
> > +{
> > +	kprobe_remove_area_blacklist(entry, entry + 1);
> > +}
> > +
> >  static void add_module_kprobe_blacklist(struct module *mod)
> >  {
> >  	unsigned long start, end;
> > @@ -2662,6 +2666,9 @@ static int kprobes_module_callback(struct notifier_block *nb,
> >  	mutex_unlock(&kprobe_mutex);
> >  	return NOTIFY_DONE;
> >  }
> > +#else
> > +#define kprobes_module_callback	(NULL)
> > +#endif /* CONFIG_MODULES */
> >  
> >  static struct notifier_block kprobe_module_nb = {
> >  	.notifier_call = kprobes_module_callback,
> > @@ -2726,7 +2733,8 @@ static int __init init_kprobes(void)
> >  	err = arch_init_kprobes();
> >  	if (!err)
> >  		err = register_die_notifier(&kprobe_exceptions_nb);
> > -	if (!err)
> > +
> > +	if (!err && IS_ENABLED(CONFIG_MODULES))
> >  		err = register_module_notifier(&kprobe_module_nb);
> >  
> >  	kprobes_initialized = (err == 0);
> > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > index 14099cc17fc9e..c509ba776e679 100644
> > --- a/kernel/trace/trace_kprobe.c
> > +++ b/kernel/trace/trace_kprobe.c
> > @@ -111,6 +111,7 @@ static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
> >  	return strncmp(module_name(mod), name, len) == 0 && name[len] == ':';
> >  }
> >  
> > +#ifdef CONFIG_MODULES
> >  static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
> >  {
> >  	char *p;
> > @@ -129,6 +130,9 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
> >  
> >  	return ret;
> >  }
> > +#else
> > +#define trace_kprobe_module_exist(tk) false /* aka a module never exists */
> > +#endif /* CONFIG_MODULES */
> >  
> >  static bool trace_kprobe_is_busy(struct dyn_event *ev)
> >  {
> > @@ -670,6 +674,7 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
> >  	return ret;
> >  }
> >  
> > +#ifdef CONFIG_MODULES
> >  /* Module notifier call back, checking event on the module */
> >  static int trace_kprobe_module_callback(struct notifier_block *nb,
> >  				       unsigned long val, void *data)
> > @@ -699,6 +704,9 @@ static int trace_kprobe_module_callback(struct notifier_block *nb,
> >  
> >  	return NOTIFY_DONE;
> >  }
> > +#else
> > +#define trace_kprobe_module_callback (NULL)
> > +#endif /* CONFIG_MODULES */
> >  
> >  static struct notifier_block trace_kprobe_module_nb = {
> >  	.notifier_call = trace_kprobe_module_callback,
> > @@ -1933,8 +1941,11 @@ static __init int init_kprobe_trace_early(void)
> >  	if (ret)
> >  		return ret;
> >  
> > -	if (register_module_notifier(&trace_kprobe_module_nb))
> > -		return -EINVAL;
> > +	if (IS_ENABLED(CONFIG_MODULES)) {
> > +		ret = register_module_notifier(&trace_kprobe_module_nb);
> > +		if (ret)
> > +			return -EINVAL;
> > +	}
> >  
> >  	return 0;
> >  }
>
> 2/4, 3/4, 4/4:
>
> Tested-by: Jarkko Sakkinen <jarkko@kernel.org> # arch/riscv

Hey, I tried the pci_proc_init example:

[    3.060703] ------------[ ftrace bug ]------------
[    3.060944] ftrace faulted on writing
[    3.060987] [<ffffffff8102c0da>] pci_proc_init+0x0/0x80
[    3.061509] Updating ftrace call site to call a different ftrace function
[    3.061756] ftrace record flags: 80100001
[    3.061925]  (1)
[    3.061925]  expected tramp: ffffffff8000aa60
[    3.062527] ------------[ cut here ]------------
[    3.062652] WARNING: CPU: 0 PID: 18 at kernel/trace/ftrace.c:2180 ftrace_bug+0x282/0x2b8
[    3.062747] CPU: 0 PID: 18 Comm: migration/0 Not tainted 6.9.0-rc1 #2
[    3.062807] Hardware name: riscv-virtio,qemu (DT)
[    3.062868] Stopper: multi_cpu_stop+0x0/0x1a0 <- stop_machine_cpuslocked+0x140/0x18c
[    3.062925] epc : ftrace_bug+0x282/0x2b8
[    3.062957]  ra : ftrace_bug+0x282/0x2b8
[    3.062989] epc : ffffffff80fc31f4 ra : ffffffff80fc31f4 sp : ff20000000093c70
[    3.063014]  gp : ffffffff824b7780 tp : ff60000002a85940 t0 : ffffffff800923a6
[    3.063037]  t1 : 0000000000000020 t2 : 6465746365707865 s0 : ff20000000093cb0
[    3.063061]  s1 : ffffffff8102c0da a0 : 0000000000000022 a1 : ffffffff8229b7f0
[    3.063084]  a2 : 0000000000000010 a3 : fffffffffffffffe a4 : 0000000000000000
[    3.063108]  a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000000000001
[    3.063131]  s2 : ff60000002850ab0 s3 : ffffffffffffffff s4 : 0000000000000002
[    3.063154]  s5 : 0000000002000000 s6 : 0000000082000000 s7 : 0000000000000000
[    3.063178]  s8 : 0000000000000001 s9 : ffffffff824bca18 s10: ff60000002845140
[    3.063202]  s11: 00000000000000ab t3 : ffffffff824ce9ef t4 : ffffffff824ce9ef
[    3.063225]  t5 : ffffffff824ce9f0 t6 : ff20000000093aa8
[    3.063248] status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000003
[    3.063331] [<ffffffff80fc31f4>] ftrace_bug+0x282/0x2b8
[    3.063398] [<ffffffff80108b1a>] ftrace_replace_code+0xfe/0x168
[    3.063430] [<ffffffff80108c82>] ftrace_modify_all_code+0x5c/0x16a
[    3.063460] [<ffffffff80108da2>] __ftrace_modify_code+0x12/0x1c
[    3.063490] [<ffffffff800f299c>] multi_cpu_stop+0x118/0x1a0
[    3.063519] [<ffffffff800f242e>] cpu_stopper_thread+0xb2/0x12a
[    3.063548] [<ffffffff8005dece>] smpboot_thread_fn+0x1aa/0x1d2
[    3.063577] [<ffffffff80057fec>] kthread+0xfe/0x106
[    3.063606] [<ffffffff80fe3d76>] ret_from_fork+0xe/0x20
[    3.063676] ---[ end trace 0000000000000000 ]---
[    3.069730] ------------[ cut here ]------------
[    3.069861] Failed to disarm kprobe-ftrace at pci_proc_init+0x0/0x80 (error -19)
[    3.070078] WARNING: CPU: 0 PID: 1 at kernel/kprobes.c:1128 __disarm_kprobe_ftrace+0x9a/0xae
[    3.070124] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G        W          6.9.0-rc1 #2
[    3.070133] Hardware name: riscv-virtio,qemu (DT)
[    3.070141] epc : __disarm_kprobe_ftrace+0x9a/0xae
[    3.070150]  ra : __disarm_kprobe_ftrace+0x9a/0xae
[    3.070157] epc : ffffffff800ffcda ra : ffffffff800ffcda sp : ff2000000000be30
[    3.070162]  gp : ffffffff824b7780 tp : ff60000002a70000 t0 : ffffffff800923a6
[    3.070167]  t1 : 0000000000000046 t2 : 6f742064656c6961 s0 : ff2000000000be60
[    3.070173]  s1 : ffffffffffffffed a0 : 0000000000000044 a1 : ffffffff8229b7f0
[    3.070178]  a2 : 0000000000000010 a3 : fffffffffffffffe a4 : 0000000000000000
[    3.070182]  a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000000000001
[    3.070187]  s2 : ffffffff824bc940 s3 : ffffffff822ac158 s4 : ff60000002b53c80
[    3.070192]  s5 : ffffffff824bc940 s6 : ffffffff822ac158 s7 : ffffffff81000000
[    3.070197]  s8 : ffffffff814775f8 s9 : ffffffff824f23d8 s10: 0000000000000000
[    3.070202]  s11: 0000000000000000 t3 : ffffffff824ce9d7 t4 : ffffffff824ce9d7
[    3.070206]  t5 : ffffffff824ce9d8 t6 : ff2000000000bc48
[    3.070211] status: 0000000200000120 badaddr: 0000000000000000 cause: 0000000000000003
[    3.070218] [<ffffffff800ffcda>] __disarm_kprobe_ftrace+0x9a/0xae
[    3.070228] [<ffffffff80101b16>] kprobe_free_init_mem+0xc2/0x130
[    3.070236] [<ffffffff80fd9b38>] kernel_init+0x46/0x14e
[    3.070245] [<ffffffff80fe3d76>] ret_from_fork+0xe/0x20
[    3.070254] ---[ end trace 0000000000000000 ]---
[

This is with riscv64 defconfig, tracing shenanigans and the following
bootconfig and the bug was realized in QEMU:

ftrace {
	tracing_on = 0
	tracer = "function_graph"
	event {
		kprobes.pci_proc_init_begin {
			probes = "pci_proc_init"
			actions = "traceon"
		}
		kprobes.pci_proc_init_end {
			probes = "pci_proc_init%return"
			actions = "traceoff"
		}
	}
}

kernel {
	console = hvc0
	dyndbg = "file arch/riscv/kernel/* +p"
	earlycon = sbi
	memblock = debug
	memtest = 1
	tp_printk
	frace_dump_on_oops
}

BR, Jarkko

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