Re: [PATCH v7 2/2] ARM: ftrace: Add MODULE_PLTS support

[Florian Fainelli <f.fainelli@gmail.com>]

Hi Qais,

On 3/23/2021 3:22 PM, Qais Yousef wrote:
> Hi Alexander
> 
> On 03/22/21 18:02, Alexander Sverdlin wrote:
>> Hi Qais,
>>
>> On 22/03/2021 17:32, Qais Yousef wrote:
>>> Yes you're right. I was a bit optimistic on CONFIG_DYNAMIC_FTRACE will imply
>>> CONFIG_ARM_MODULE_PLTS is enabled too.
>>>
>>> It only has an impact on reducing ifdefery when calling
>>>
>>> 	ftrace_call_replace_mod(rec->arch.mod, ...)
>>>
>>> Should be easy to wrap rec->arch.mod with its own accessor that will return
>>> NULL if !CONFIG_ARM_MODULE_PLTS or just ifdef the functions.
>>>
>>> Up to Alexander to pick what he prefers :-)
>>
>> well, I of course prefer v7 as-is, because this review is running longer than two
>> years and I actually hope these patches to be finally merged at some point.
>> But you are welcome to optimize them with follow up patches :)
> 
> I appreciate that and thanks a lot for your effort. My attempt to review and
> test here is to help in getting this merged.
> 
> FWIW my main concern is about duplicating the range check in
> ftrace_call_replace() and using magic values that already exist in
> __arm_gen_branch_{arm, thumb2}() and better remain encapsulated there.

Your patch in addition to Alexander's patch work for me as well, so feel
free to add a:

Tested-by: Florian Fainelli <f.fainelli@gmail.com>

FWIW, what is nice about Alexander's original patch is that it applies
relatively cleanly to older kernels as well where this is equally
needed. There is not currently any Fixes: tag being provided but maybe
we should amend the second patch with one?

Thanks!

> 
> Thanks
> 
> --
> Qais Yousef
> 
> ----->8------
> 
> 
> diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
> index a4dbac07e4ef..8545b3ff8317 100644
> --- a/arch/arm/include/asm/ftrace.h
> +++ b/arch/arm/include/asm/ftrace.h
> @@ -25,6 +25,27 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
>  	/* With Thumb-2, the recorded addresses have the lsb set */
>  	return addr & ~1;
>  }
> +
> +#ifdef CONFIG_ARM_MODULE_PLTS
> +static inline void ftrace_set_mod(struct dyn_arch_ftrace *arch, struct module *mod)
> +{
> +	arch->mod = mod;
> +}
> +
> +static inline struct module *ftrace_get_mod(struct dyn_arch_ftrace *arch)
> +{
> +	return arch->mod;
> +}
> +#else
> +static inline void ftrace_set_mod(struct dyn_arch_ftrace *arch, struct module *mod)
> +{
> +}
> +
> +static inline struct module *ftrace_get_mod(struct dyn_arch_ftrace *arch)
> +{
> +	return NULL;
> +}
> +#endif
>  #endif
>  
>  #endif
> diff --git a/arch/arm/include/asm/insn.h b/arch/arm/include/asm/insn.h
> index f20e08ac85ae..71c3edefe629 100644
> --- a/arch/arm/include/asm/insn.h
> +++ b/arch/arm/include/asm/insn.h
> @@ -13,18 +13,24 @@ arm_gen_nop(void)
>  }
>  
>  unsigned long
> -__arm_gen_branch(unsigned long pc, unsigned long addr, bool link);
> +__arm_gen_branch(unsigned long pc, unsigned long addr, bool link, bool check);
>  
>  static inline unsigned long
>  arm_gen_branch(unsigned long pc, unsigned long addr)
>  {
> -	return __arm_gen_branch(pc, addr, false);
> +	return __arm_gen_branch(pc, addr, false, true);
>  }
>  
>  static inline unsigned long
>  arm_gen_branch_link(unsigned long pc, unsigned long addr)
>  {
> -	return __arm_gen_branch(pc, addr, true);
> +	return __arm_gen_branch(pc, addr, true, true);
> +}
> +
> +static inline unsigned long
> +arm_gen_branch_link_nocheck(unsigned long pc, unsigned long addr)
> +{
> +	return __arm_gen_branch(pc, addr, true, false);
>  }
>  
>  #endif
> diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
> index fa867a57100f..63ea34edd222 100644
> --- a/arch/arm/kernel/ftrace.c
> +++ b/arch/arm/kernel/ftrace.c
> @@ -70,20 +70,28 @@ int ftrace_arch_code_modify_post_process(void)
>  
>  static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
>  {
> -	s32 offset = addr - pc;
> -	s32 blim = 0xfe000008;
> -	s32 flim = 0x02000004;
> +	return arm_gen_branch_link(pc, addr);
> +}
>  
> -	if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
> -		blim = 0xff000004;
> -		flim = 0x01000002;
> -	}
> +static unsigned long
> +ftrace_call_replace_mod(struct module *mod, unsigned long pc, unsigned long addr)
> +{
> +#ifdef CONFIG_ARM_MODULE_PLTS
> +	unsigned long new;
>  
> -	if (IS_ENABLED(CONFIG_ARM_MODULE_PLTS) &&
> -	    (offset < blim || offset > flim))
> -		return 0;
> +	if (likely(!mod))
> +		return arm_gen_branch_link(pc, addr);
>  
> +	new = arm_gen_branch_link_nocheck(pc, addr);
> +	if (!new) {
> +		addr = get_module_plt(mod, pc, addr);
> +		new = arm_gen_branch_link(pc, addr);
> +	}
> +
> +	return new;
> +#else
>  	return arm_gen_branch_link(pc, addr);
> +#endif
>  }
>  
>  static int ftrace_modify_code(unsigned long pc, unsigned long old,
> @@ -141,18 +149,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
>  
>  	old = ftrace_nop_replace(rec);
>  
> -	new = ftrace_call_replace(ip, aaddr);
> -
> -#ifdef CONFIG_ARM_MODULE_PLTS
> -	if (!new) {
> -		struct module *mod = rec->arch.mod;
> -
> -		if (mod) {
> -			aaddr = get_module_plt(mod, ip, aaddr);
> -			new = ftrace_call_replace(ip, aaddr);
> -		}
> -	}
> -#endif
> +	new = ftrace_call_replace_mod(ftrace_get_mod(&rec->arch), ip, aaddr);
>  
>  	return ftrace_modify_code(rec->ip, old, new, true);
>  }
> @@ -183,23 +180,11 @@ int ftrace_make_nop(struct module *mod,
>  	unsigned long new;
>  	int ret;
>  
> -#ifdef CONFIG_ARM_MODULE_PLTS
>  	/* mod is only supplied during module loading */
> -	if (!mod)
> -		mod = rec->arch.mod;
> -	else
> -		rec->arch.mod = mod;
> -#endif
> -
> -	old = ftrace_call_replace(ip, aaddr);
> -
> -#ifdef CONFIG_ARM_MODULE_PLTS
> -	if (!old && mod) {
> -		aaddr = get_module_plt(mod, ip, aaddr);
> -		old = ftrace_call_replace(ip, aaddr);
> -	}
> -#endif
> +	if (mod)
> +		ftrace_set_mod(&rec->arch, mod);
>  
> +	old = ftrace_call_replace_mod(ftrace_get_mod(&rec->arch), ip, aaddr);
>  	new = ftrace_nop_replace(rec);
>  	ret = ftrace_modify_code(ip, old, new, true);
>  
> diff --git a/arch/arm/kernel/insn.c b/arch/arm/kernel/insn.c
> index 2e844b70386b..37ec5734309e 100644
> --- a/arch/arm/kernel/insn.c
> +++ b/arch/arm/kernel/insn.c
> @@ -4,7 +4,7 @@
>  #include <asm/opcodes.h>
>  
>  static unsigned long
> -__arm_gen_branch_thumb2(unsigned long pc, unsigned long addr, bool link)
> +__arm_gen_branch_thumb2(unsigned long pc, unsigned long addr, bool link, bool check)
>  {
>  	unsigned long s, j1, j2, i1, i2, imm10, imm11;
>  	unsigned long first, second;
> @@ -12,7 +12,7 @@ __arm_gen_branch_thumb2(unsigned long pc, unsigned long addr, bool link)
>  
>  	offset = (long)addr - (long)(pc + 4);
>  	if (offset < -16777216 || offset > 16777214) {
> -		WARN_ON_ONCE(1);
> +		WARN_ON_ONCE(check);
>  		return 0;
>  	}
>  
> @@ -34,7 +34,7 @@ __arm_gen_branch_thumb2(unsigned long pc, unsigned long addr, bool link)
>  }
>  
>  static unsigned long
> -__arm_gen_branch_arm(unsigned long pc, unsigned long addr, bool link)
> +__arm_gen_branch_arm(unsigned long pc, unsigned long addr, bool link, bool check)
>  {
>  	unsigned long opcode = 0xea000000;
>  	long offset;
> @@ -44,7 +44,7 @@ __arm_gen_branch_arm(unsigned long pc, unsigned long addr, bool link)
>  
>  	offset = (long)addr - (long)(pc + 8);
>  	if (unlikely(offset < -33554432 || offset > 33554428)) {
> -		WARN_ON_ONCE(1);
> +		WARN_ON_ONCE(check);
>  		return 0;
>  	}
>  
> @@ -54,10 +54,10 @@ __arm_gen_branch_arm(unsigned long pc, unsigned long addr, bool link)
>  }
>  
>  unsigned long
> -__arm_gen_branch(unsigned long pc, unsigned long addr, bool link)
> +__arm_gen_branch(unsigned long pc, unsigned long addr, bool link, bool check)
>  {
>  	if (IS_ENABLED(CONFIG_THUMB2_KERNEL))
> -		return __arm_gen_branch_thumb2(pc, addr, link);
> +		return __arm_gen_branch_thumb2(pc, addr, link, check);
>  	else
> -		return __arm_gen_branch_arm(pc, addr, link);
> +		return __arm_gen_branch_arm(pc, addr, link, check);
>  }
> 

-- 
Florian