Messages in this thread Patch in this message | | | Date | Fri, 8 Mar 2019 13:31:43 +0100 | From | Jessica Yu <> | Subject | Re: [PATCH] kallsyms: store type information in its own array |
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+++ Eugene Loh [07/03/19 15:37 -0800]: >It's been 1.5 weeks. Could I get some feedback on this patch? Thanks.
Apologies, I was on vacation the past week.
Added some CC's from the last time we talked about overwriting the st_size/st_info Elf_Sym fields, in case anyone else has comments.
>On 02/25/2019 11:59 AM, eugene.loh@oracle.com wrote: >>From: Eugene Loh <eugene.loh@oracle.com> >> >>When a module is loaded, its symbols' Elf_Sym information is stored >>in a symtab. Further, type information is also captured. Since >>Elf_Sym has no type field, historically the st_info field has been >>hijacked for storing type: st_info was overwritten. >> >>commit 5439c985c5a83a8419f762115afdf560ab72a452 ("module: Overwrite >>st_size instead of st_info") changes that practice, as its one-liner >>indicates. Unfortunately, this change overwrites symbol size, >>information that a tool like DTrace expects to find. >> >>Allocate a typetab array to store type information so that no Elf_Sym >>field needs to be overwritten. >> >>Fixes: 5439c985c5a8 ("module: Overwrite st_size instead of st_info") >>Signed-off-by: Eugene Loh <eugene.loh@oracle.com> >>Reviewed-by: Nick Alcock <nick.alcock@oracle.com> >>--- >> include/linux/module.h | 1 + >> kernel/module-internal.h | 2 +- >> kernel/module.c | 21 ++++++++++++++------- >> 3 files changed, 16 insertions(+), 8 deletions(-) >> >>diff --git a/include/linux/module.h b/include/linux/module.h >>index f5bc4c0..9c1bc21 100644 >>--- a/include/linux/module.h >>+++ b/include/linux/module.h >>@@ -315,6 +315,7 @@ struct mod_kallsyms { >> Elf_Sym *symtab; >> unsigned int num_symtab; >> char *strtab; >>+ char *typetab; >> }; >> #ifdef CONFIG_LIVEPATCH >>diff --git a/kernel/module-internal.h b/kernel/module-internal.h >>index 79c9be2..67828af 100644 >>--- a/kernel/module-internal.h >>+++ b/kernel/module-internal.h >>@@ -20,7 +20,7 @@ struct load_info { >> unsigned long len; >> Elf_Shdr *sechdrs; >> char *secstrings, *strtab; >>- unsigned long symoffs, stroffs; >>+ unsigned long symoffs, stroffs, init_typeoff, core_typeoff;
Small nit: typeoff to typeoffs to match symoffs and stroffs.
Otherwise the rest looks fine to me. I guess it's about time we get rid of the Elf_Sym field hijacking anyway :-)
Thanks!
Jessica
>> struct _ddebug *debug; >> unsigned int num_debug; >> bool sig_ok; >>diff --git a/kernel/module.c b/kernel/module.c >>index 2ad1b52..c7c1bcd 100644 >>--- a/kernel/module.c >>+++ b/kernel/module.c >>@@ -2647,6 +2647,8 @@ static void layout_symtab(struct module *mod, struct load_info *info) >> info->symoffs = ALIGN(mod->core_layout.size, symsect->sh_addralign ?: 1); >> info->stroffs = mod->core_layout.size = info->symoffs + ndst * sizeof(Elf_Sym); >> mod->core_layout.size += strtab_size; >>+ info->core_typeoff = mod->core_layout.size; >>+ mod->core_layout.size += ndst * sizeof(char); >> mod->core_layout.size = debug_align(mod->core_layout.size); >> /* Put string table section at end of init part of module. */ >>@@ -2660,6 +2662,8 @@ static void layout_symtab(struct module *mod, struct load_info *info) >> __alignof__(struct mod_kallsyms)); >> info->mod_kallsyms_init_off = mod->init_layout.size; >> mod->init_layout.size += sizeof(struct mod_kallsyms); >>+ info->init_typeoff = mod->init_layout.size; >>+ mod->init_layout.size += nsrc * sizeof(char); >> mod->init_layout.size = debug_align(mod->init_layout.size); >> } >>@@ -2683,20 +2687,23 @@ static void add_kallsyms(struct module *mod, const struct load_info *info) >> mod->kallsyms->num_symtab = symsec->sh_size / sizeof(Elf_Sym); >> /* Make sure we get permanent strtab: don't use info->strtab. */ >> mod->kallsyms->strtab = (void *)info->sechdrs[info->index.str].sh_addr; >>+ mod->kallsyms->typetab = mod->init_layout.base + info->init_typeoff; >>- /* Set types up while we still have access to sections. */ >>- for (i = 0; i < mod->kallsyms->num_symtab; i++) >>- mod->kallsyms->symtab[i].st_size >>- = elf_type(&mod->kallsyms->symtab[i], info); >>- >>- /* Now populate the cut down core kallsyms for after init. */ >>+ /* >>+ * Now populate the cut down core kallsyms for after init >>+ * and set types up while we still have access to sections. >>+ */ >> mod->core_kallsyms.symtab = dst = mod->core_layout.base + info->symoffs; >> mod->core_kallsyms.strtab = s = mod->core_layout.base + info->stroffs; >>+ mod->core_kallsyms.typetab = mod->core_layout.base + info->core_typeoff; >> src = mod->kallsyms->symtab; >> for (ndst = i = 0; i < mod->kallsyms->num_symtab; i++) { >>+ mod->kallsyms->typetab[i] = elf_type(src + i, info); >> if (i == 0 || is_livepatch_module(mod) || >> is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum, >> info->index.pcpu)) { >>+ mod->core_kallsyms.typetab[ndst] = >>+ mod->kallsyms->typetab[i]; >> dst[ndst] = src[i]; >> dst[ndst++].st_name = s - mod->core_kallsyms.strtab; >> s += strlcpy(s, &mod->kallsyms->strtab[src[i].st_name], >>@@ -4084,7 +4091,7 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type, >> const Elf_Sym *sym = &kallsyms->symtab[symnum]; >> *value = kallsyms_symbol_value(sym); >>- *type = sym->st_size; >>+ *type = kallsyms->typetab[symnum]; >> strlcpy(name, kallsyms_symbol_name(kallsyms, symnum), KSYM_NAME_LEN); >> strlcpy(module_name, mod->name, MODULE_NAME_LEN); >> *exported = is_exported(name, *value, mod); >
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