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

Chen Zhongjin
2022-03-31T02:19:08Z

Gentle ping for comment. Thanks for your time!

On 2022/3/25 9:12, 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>
> ---
> arch/arm/include/asm/module.h | 17 ++------
> arch/arm/include/asm/unwind.h | 1 +
> arch/arm/kernel/module.c | 73 +++++++++++++++++------------------
> 3 files changed, 40 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..272f9bdeb1ed 100644
> --- a/arch/arm/kernel/module.c
> +++ b/arch/arm/kernel/module.c
> @@ -459,46 +459,36 @@ 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 *table_list = &mod->arch.unwind_list;
>
> - memset(maps, 0, sizeof(maps));
> + INIT_LIST_HEAD(&table_list->mod_list);
> + mod->arch.init_table = NULL;
>
> for (s = sechdrs; s < sechdrs_end; s++) {
> - const char *secname = secstrs + s->sh_name;
> + const unsigned int sectype = s->sh_type;
>
> if (!(s->sh_flags & SHF_ALLOC))
> 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 (sectype == ELF_SECTION_UNWIND) {
> + const char *secname = secstrs + s->sh_name;
> + const char *txtname = strcmp(".ARM.exidx", secname) == 0 ?
> + ".text" : secname + strlen(".ARM.exidx");
> + const Elf_Shdr *txt_sec = find_mod_section(hdr, sechdrs, txtname);
> +
> + 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, &table_list->mod_list);
> + /* save init table for module_arch_freeing_init */
> + if (strcmp(".ARM.exidx.init.text", secname) == 0)
> + mod->arch.init_table = table;
> + }
> + }
> }
> -
> - 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);
> #endif
> #ifdef CONFIG_ARM_PATCH_PHYS_VIRT
> s = find_mod_section(hdr, sechdrs, ".pv_table");
> @@ -519,11 +509,13 @@ 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 +523,12 @@ 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
> }