Re: [PATCH v4] ARM: module: Add all unwind tables when load module

[Chen Zhongjin <chenzhongjin@huawei.com>]

ping for review, thanks!

On 2022/4/1 21:15, Chen Zhongjin wrote:
> For EABI stack unwinding, when loading .ko module
> the EXIDX sections will be added to a unwind_table list.
> 
> However not all EXIDX sections are added because EXIDX
> sections are searched by hardcoded section names.
> 
> For functions in other sections such as .ref.text
> or .kprobes.text, gcc generates seprated EXIDX sections
> (such as .ARM.exidx.ref.text or .ARM.exidx.kprobes.text).
> 
> These extra EXIDX sections are not loaded, so when unwinding
> functions in these sections, we will failed with:
> 
> 	unwind: Index not found xxx
> 
> To fix that, I refactor the code for searching and adding
> EXIDX sections:
> 
> - Check section type to search EXIDX tables (0x70000001)
> instead of strcmp() the hardcoded names. Then find the
> corresponding text sections by their section names.
> 
> - Add a unwind_table list in module->arch to save their own
> unwind_table instead of the fixed-lenth array.
> 
> - Save .ARM.exidx.init.text section ptr, because it should
> be cleaned after module init.
> 
> Now all EXIDX sections of .ko can be added correctly.
> 
> Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
> ---
> Changes v3 -> v4:
> - Fix indent by replace tab with code.
> 
> Changes v2 -> v3:
> - Unwind "txtname" and add some blank, to make code more clear.
> 
> Changes v1 -> v2:
> - Rename "table_list" to "unwind_list" for consistency.
> - Drop unnecessary locals variable "txtname" and "sectype".
> - Merge condition checks for sh_flags and sh_type.
> ---
>  arch/arm/include/asm/module.h | 17 ++------
>  arch/arm/include/asm/unwind.h |  1 +
>  arch/arm/kernel/module.c      | 78 ++++++++++++++++++-----------------
>  3 files changed, 45 insertions(+), 51 deletions(-)
> 
> diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h
> index cfffae67c04e..8139b6a33a22 100644
> --- a/arch/arm/include/asm/module.h
> +++ b/arch/arm/include/asm/module.h
> @@ -3,20 +3,10 @@
>  #define _ASM_ARM_MODULE_H
>  
>  #include <asm-generic/module.h>
> -
> -struct unwind_table;
> +#include <asm/unwind.h>
>  
>  #ifdef CONFIG_ARM_UNWIND
> -enum {
> -	ARM_SEC_INIT,
> -	ARM_SEC_DEVINIT,
> -	ARM_SEC_CORE,
> -	ARM_SEC_EXIT,
> -	ARM_SEC_DEVEXIT,
> -	ARM_SEC_HOT,
> -	ARM_SEC_UNLIKELY,
> -	ARM_SEC_MAX,
> -};
> +#define ELF_SECTION_UNWIND 0x70000001
>  #endif
>  
>  #define PLT_ENT_STRIDE		L1_CACHE_BYTES
> @@ -36,7 +26,8 @@ struct mod_plt_sec {
>  
>  struct mod_arch_specific {
>  #ifdef CONFIG_ARM_UNWIND
> -	struct unwind_table *unwind[ARM_SEC_MAX];
> +	struct unwind_table unwind_list;
> +	struct unwind_table *init_table;
>  #endif
>  #ifdef CONFIG_ARM_MODULE_PLTS
>  	struct mod_plt_sec	core;
> diff --git a/arch/arm/include/asm/unwind.h b/arch/arm/include/asm/unwind.h
> index 0f8a3439902d..b51f85417f58 100644
> --- a/arch/arm/include/asm/unwind.h
> +++ b/arch/arm/include/asm/unwind.h
> @@ -24,6 +24,7 @@ struct unwind_idx {
>  
>  struct unwind_table {
>  	struct list_head list;
> +	struct list_head mod_list;
>  	const struct unwind_idx *start;
>  	const struct unwind_idx *origin;
>  	const struct unwind_idx *stop;
> diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
> index 549abcedf795..b98bcb47e337 100644
> --- a/arch/arm/kernel/module.c
> +++ b/arch/arm/kernel/module.c
> @@ -459,46 +459,41 @@ int module_finalize(const Elf32_Ehdr *hdr, const Elf_Shdr *sechdrs,
>  #ifdef CONFIG_ARM_UNWIND
>  	const char *secstrs = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
>  	const Elf_Shdr *sechdrs_end = sechdrs + hdr->e_shnum;
> -	struct mod_unwind_map maps[ARM_SEC_MAX];
> -	int i;
> +	struct unwind_table *unwind_list = &mod->arch.unwind_list;
>  
> -	memset(maps, 0, sizeof(maps));
> +	INIT_LIST_HEAD(&unwind_list->mod_list);
> +	mod->arch.init_table = NULL;
>  
>  	for (s = sechdrs; s < sechdrs_end; s++) {
>  		const char *secname = secstrs + s->sh_name;
> +		const char *txtname;
> +		const Elf_Shdr *txt_sec;
>  
> -		if (!(s->sh_flags & SHF_ALLOC))
> +		if (!strcmp(".ARM.exidx", secname))
> +			txtname = ".text";
> +		else
> +			txtname = secname + strlen(".ARM.exidx");
> +
> +		txt_sec = find_mod_section(hdr, sechdrs, txtname);
> +
> +		if (!(s->sh_flags & SHF_ALLOC) ||
> +		    s->sh_type != ELF_SECTION_UNWIND)
>  			continue;
>  
> -		if (strcmp(".ARM.exidx.init.text", secname) == 0)
> -			maps[ARM_SEC_INIT].unw_sec = s;
> -		else if (strcmp(".ARM.exidx", secname) == 0)
> -			maps[ARM_SEC_CORE].unw_sec = s;
> -		else if (strcmp(".ARM.exidx.exit.text", secname) == 0)
> -			maps[ARM_SEC_EXIT].unw_sec = s;
> -		else if (strcmp(".ARM.exidx.text.unlikely", secname) == 0)
> -			maps[ARM_SEC_UNLIKELY].unw_sec = s;
> -		else if (strcmp(".ARM.exidx.text.hot", secname) == 0)
> -			maps[ARM_SEC_HOT].unw_sec = s;
> -		else if (strcmp(".init.text", secname) == 0)
> -			maps[ARM_SEC_INIT].txt_sec = s;
> -		else if (strcmp(".text", secname) == 0)
> -			maps[ARM_SEC_CORE].txt_sec = s;
> -		else if (strcmp(".exit.text", secname) == 0)
> -			maps[ARM_SEC_EXIT].txt_sec = s;
> -		else if (strcmp(".text.unlikely", secname) == 0)
> -			maps[ARM_SEC_UNLIKELY].txt_sec = s;
> -		else if (strcmp(".text.hot", secname) == 0)
> -			maps[ARM_SEC_HOT].txt_sec = s;
> -	}
> +		if (txt_sec) {
> +			struct unwind_table *table =
> +				unwind_table_add(s->sh_addr,
> +						s->sh_size,
> +						txt_sec->sh_addr,
> +						txt_sec->sh_size);
> +
> +			list_add(&table->mod_list, &unwind_list->mod_list);
>  
> -	for (i = 0; i < ARM_SEC_MAX; i++)
> -		if (maps[i].unw_sec && maps[i].txt_sec)
> -			mod->arch.unwind[i] =
> -				unwind_table_add(maps[i].unw_sec->sh_addr,
> -					         maps[i].unw_sec->sh_size,
> -					         maps[i].txt_sec->sh_addr,
> -					         maps[i].txt_sec->sh_size);
> +			/* save init table for module_arch_freeing_init */
> +			if (strcmp(".ARM.exidx.init.text", secname) == 0)
> +				mod->arch.init_table = table;
> +		}
> +	}
>  #endif
>  #ifdef CONFIG_ARM_PATCH_PHYS_VIRT
>  	s = find_mod_section(hdr, sechdrs, ".pv_table");
> @@ -519,11 +514,13 @@ void
>  module_arch_cleanup(struct module *mod)
>  {
>  #ifdef CONFIG_ARM_UNWIND
> -	int i;
> +	struct unwind_table *tmp;
> +	struct unwind_table *n;
>  
> -	for (i = 0; i < ARM_SEC_MAX; i++) {
> -		unwind_table_del(mod->arch.unwind[i]);
> -		mod->arch.unwind[i] = NULL;
> +	list_for_each_entry_safe(tmp, n,
> +			&mod->arch.unwind_list.mod_list, mod_list) {
> +		list_del(&tmp->mod_list);
> +		unwind_table_del(tmp);
>  	}
>  #endif
>  }
> @@ -531,7 +528,12 @@ module_arch_cleanup(struct module *mod)
>  void __weak module_arch_freeing_init(struct module *mod)
>  {
>  #ifdef CONFIG_ARM_UNWIND
> -	unwind_table_del(mod->arch.unwind[ARM_SEC_INIT]);
> -	mod->arch.unwind[ARM_SEC_INIT] = NULL;
> +	struct unwind_table *init = mod->arch.init_table;
> +
> +	if (init) {
> +		mod->arch.init_table = NULL;
> +		list_del(&init->mod_list);
> +		unwind_table_del(init);
> +	}
>  #endif
>  }