Re: [PATCH v6 08/17] static_call: Avoid kprobes on inline static_call()s

[Steven Rostedt]

On Fri, 10 Jul 2020 15:38:39 +0200
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> Similar to how we disallow kprobes on any other dynamic text
> (ftrace/jump_label) also disallow kprobes on inline static_call()s.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>

I'd like to have Masami review this patch too.

> ---
>  arch/x86/kernel/kprobes/opt.c |    4 +-
>  include/linux/static_call.h   |   11 +++++++
>  kernel/kprobes.c              |    2 +
>  kernel/static_call.c          |   64 ++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 80 insertions(+), 1 deletion(-)
> 
> --- a/arch/x86/kernel/kprobes/opt.c
> +++ b/arch/x86/kernel/kprobes/opt.c
> @@ -17,6 +17,7 @@
>  #include <linux/ftrace.h>
>  #include <linux/frame.h>
>  #include <linux/pgtable.h>
> +#include <linux/static_call.h>
>  
>  #include <asm/text-patching.h>
>  #include <asm/cacheflush.h>
> @@ -209,7 +210,8 @@ static int copy_optimized_instructions(u
>  	/* Check whether the address range is reserved */
>  	if (ftrace_text_reserved(src, src + len - 1) ||
>  	    alternatives_text_reserved(src, src + len - 1) ||
> -	    jump_label_text_reserved(src, src + len - 1))
> +	    jump_label_text_reserved(src, src + len - 1) ||
> +	    static_call_text_reserved(src, src + len - 1))
>  		return -EBUSY;
>  
>  	return len;
> --- a/include/linux/static_call.h
> +++ b/include/linux/static_call.h
> @@ -110,6 +110,7 @@ struct static_call_key {
>  
>  extern void __static_call_update(struct static_call_key *key, void *tramp, void *func);
>  extern int static_call_mod_init(struct module *mod);
> +extern int static_call_text_reserved(void *start, void *end);
>  
>  #define DEFINE_STATIC_CALL(name, _func)					\
>  	DECLARE_STATIC_CALL(name, _func);				\
> @@ -153,6 +154,11 @@ void __static_call_update(struct static_
>  	cpus_read_unlock();
>  }
>  
> +static inline int static_call_text_reserved(void *start, void *end)
> +{
> +	return 0;
> +}
> +
>  #define EXPORT_STATIC_CALL(name)					\
>  	EXPORT_SYMBOL(STATIC_CALL_KEY(name));				\
>  	EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))
> @@ -182,6 +188,11 @@ void __static_call_update(struct static_
>  	WRITE_ONCE(key->func, func);
>  }
>  
> +static inline int static_call_text_reserved(void *start, void *end)
> +{
> +	return 0;
> +}
> +
>  #define EXPORT_STATIC_CALL(name)	EXPORT_SYMBOL(STATIC_CALL_KEY(name))
>  #define EXPORT_STATIC_CALL_GPL(name)	EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name))
>  
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -35,6 +35,7 @@
>  #include <linux/ftrace.h>
>  #include <linux/cpu.h>
>  #include <linux/jump_label.h>
> +#include <linux/static_call.h>
>  
>  #include <asm/sections.h>
>  #include <asm/cacheflush.h>
> @@ -1591,6 +1592,7 @@ static int check_kprobe_address_safe(str
>  	if (!kernel_text_address((unsigned long) p->addr) ||
>  	    within_kprobe_blacklist((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)) {
>  		ret = -EINVAL;
>  		goto out;
> --- a/kernel/static_call.c
> +++ b/kernel/static_call.c
> @@ -204,8 +204,58 @@ static int __static_call_init(struct mod
>  	return 0;
>  }
>  
> +static int addr_conflict(struct static_call_site *site, void *start, void *end)
> +{
> +	unsigned long addr = (unsigned long)static_call_addr(site);
> +
> +	if (addr <= (unsigned long)end &&
> +	    addr + CALL_INSN_SIZE > (unsigned long)start)
> +		return 1;
> +
> +	return 0;
> +}
> +
> +static int __static_call_text_reserved(struct static_call_site *iter_start,
> +				       struct static_call_site *iter_stop,
> +				       void *start, void *end)
> +{
> +	struct static_call_site *iter = iter_start;
> +
> +	while (iter < iter_stop) {
> +		if (addr_conflict(iter, start, end))
> +			return 1;
> +		iter++;
> +	}
> +
> +	return 0;
> +}
> +
>  #ifdef CONFIG_MODULES
>  
> +static int __static_call_mod_text_reserved(void *start, void *end)
> +{
> +	struct module *mod;
> +	int ret;
> +
> +	preempt_disable();
> +	mod = __module_text_address((unsigned long)start);
> +	WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
> +	if (!try_module_get(mod))
> +		mod = NULL;
> +	preempt_enable();
> +
> +	if (!mod)
> +		return 0;
> +
> +	ret = __static_call_text_reserved(mod->static_call_sites,
> +			mod->static_call_sites + mod->num_static_call_sites,
> +			start, end);
> +
> +	module_put(mod);
> +
> +	return ret;
> +}
> +
>  static int static_call_add_module(struct module *mod)
>  {
>  	return __static_call_init(mod, mod->static_call_sites,
> @@ -275,6 +325,20 @@ static struct notifier_block static_call
>  
>  #endif /* CONFIG_MODULES */
>  
> +int static_call_text_reserved(void *start, void *end)
> +{
> +	int ret = __static_call_text_reserved(__start_static_call_sites,
> +			__stop_static_call_sites, start, end);
> +
> +	if (ret)
> +		return ret;
> +
> +#ifdef CONFIG_MODULES
> +	ret = __static_call_mod_text_reserved(start, end);
> +#endif

Nit, but why not have a #else /* !CONFIG_MODULE */ above and just:

static inline int __static_call_mod_text_reserve(..)
{
	return 0;
}
#endif

?

Then you don't need the extra #ifdef above, and just end it with:

	return __static_call_mod_next_reserved(start, end);

-- Steve


> +	return ret;
> +}
> +
>  static void __init static_call_init(void)
>  {
>  	int ret;
>