linux-kernel - Re: [PATCH 1/3] init: Declare rodata_enabled and mark_rodata

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Date: Thu, 21 Dec 2023 21:35:26 -0800
From: Kees Cook <kees@...nel.org>
To: Michael Ellerman <mpe@...erman.id.au>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Nicholas Piggin <npiggin@...il.com>, Arnd Bergmann <arnd@...db.de>,
 Luis Chamberlain <mcgrof@...nel.org>
CC: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 linux-modules@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 1/3] init: Declare rodata_enabled and mark_rodata_ro() at all time



On December 21, 2023 4:16:56 AM PST, Michael Ellerman <mpe@...erman.id.au> wrote:
>Cc +Kees
>
>Christophe Leroy <christophe.leroy@...roup.eu> writes:
>> Declaring rodata_enabled and mark_rodata_ro() at all time
>> helps removing related #ifdefery in C files.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>> ---
>>  include/linux/init.h |  4 ----
>>  init/main.c          | 21 +++++++--------------
>>  2 files changed, 7 insertions(+), 18 deletions(-)
>>
>> diff --git a/include/linux/init.h b/include/linux/init.h
>> index 01b52c9c7526..d2b47be38a07 100644
>> --- a/include/linux/init.h
>> +++ b/include/linux/init.h
>> @@ -168,12 +168,8 @@ extern initcall_entry_t __initcall_end[];
>>  
>>  extern struct file_system_type rootfs_fs_type;
>>  
>> -#if defined(CONFIG_STRICT_KERNEL_RWX) || defined(CONFIG_STRICT_MODULE_RWX)
>>  extern bool rodata_enabled;
>> -#endif
>> -#ifdef CONFIG_STRICT_KERNEL_RWX
>>  void mark_rodata_ro(void);
>> -#endif
>>  
>>  extern void (*late_time_init)(void);
>>  
>> diff --git a/init/main.c b/init/main.c
>> index e24b0780fdff..807df08c501f 100644
>> --- a/init/main.c
>> +++ b/init/main.c
>> @@ -1396,10 +1396,9 @@ static int __init set_debug_rodata(char *str)
>>  early_param("rodata", set_debug_rodata);
>>  #endif
>>  
>> -#ifdef CONFIG_STRICT_KERNEL_RWX
>>  static void mark_readonly(void)
>>  {
>> -	if (rodata_enabled) {
>> +	if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX) && rodata_enabled) {

I think this will break without rodata_enabled actual existing on other architectures. (Only declaration was made visible, not the definition, which is above here and still behind ifdefs?)

-Kees

>>  		/*
>>  		 * load_module() results in W+X mappings, which are cleaned
>>  		 * up with call_rcu().  Let's make sure that queued work is
>> @@ -1409,20 +1408,14 @@ static void mark_readonly(void)
>>  		rcu_barrier();
>>  		mark_rodata_ro();
>>  		rodata_test();
>> -	} else
>> +	} else if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX)) {
>>  		pr_info("Kernel memory protection disabled.\n");
>> +	} else if (IS_ENABLED(CONFIG_ARCH_HAS_STRICT_KERNEL_RWX)) {
>> +		pr_warn("Kernel memory protection not selected by kernel config.\n");
>> +	} else {
>> +		pr_warn("This architecture does not have kernel memory protection.\n");
>> +	}
>>  }
>> -#elif defined(CONFIG_ARCH_HAS_STRICT_KERNEL_RWX)
>> -static inline void mark_readonly(void)
>> -{
>> -	pr_warn("Kernel memory protection not selected by kernel config.\n");
>> -}
>> -#else
>> -static inline void mark_readonly(void)
>> -{
>> -	pr_warn("This architecture does not have kernel memory protection.\n");
>> -}
>> -#endif
>>  
>>  void __weak free_initmem(void)
>>  {
>> -- 
>> 2.41.0

-- 
Kees Cook