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    SubjectRe: livepatch: reuse module loader code to write relocations
    +++ Josh Poimboeuf [08/02/16 14:26 -0600]:
    >On Wed, Feb 03, 2016 at 08:11:09PM -0500, Jessica Yu wrote:
    >> Reuse module loader code to write relocations, thereby eliminating the need
    >> for architecture specific relocation code in livepatch. Specifically, reuse
    >> the apply_relocate_add() function in the module loader to write relocations
    >> instead of duplicating functionality in livepatch's arch-dependent
    >> klp_write_module_reloc() function.
    >>
    >> In order to accomplish this, livepatch modules manage their own relocation
    >> sections (marked with the SHF_RELA_LIVEPATCH section flag) and
    >> livepatch-specific symbols (marked with SHN_LIVEPATCH symbol section
    >> index). To apply livepatch relocation sections, livepatch symbols
    >> referenced by relocs are resolved and then apply_relocate_add() is called
    >> to apply those relocations.
    >>
    >> In addition, remove x86 livepatch relocation code and the s390
    >> klp_write_module_reloc() function stub. They are no longer needed since
    >> relocation work has been offloaded to module loader.
    >>
    >> Signed-off-by: Jessica Yu <jeyu@redhat.com>
    >> ---
    >> arch/s390/include/asm/livepatch.h | 7 -
    >> arch/x86/include/asm/livepatch.h | 2 -
    >> arch/x86/kernel/Makefile | 1 -
    >> arch/x86/kernel/livepatch.c | 70 ----------
    >> include/linux/livepatch.h | 30 ++--
    >> kernel/livepatch/core.c | 283 ++++++++++++++++++++++++++++++--------
    >> 6 files changed, 238 insertions(+), 155 deletions(-)
    >> delete mode 100644 arch/x86/kernel/livepatch.c
    >>
    >> diff --git a/arch/s390/include/asm/livepatch.h b/arch/s390/include/asm/livepatch.h
    >> index a52b6cc..350a751 100644
    >> --- a/arch/s390/include/asm/livepatch.h
    >> +++ b/arch/s390/include/asm/livepatch.h
    >> @@ -25,13 +25,6 @@ static inline int klp_check_compiler_support(void)
    >> return 0;
    >> }
    >>
    >> -static inline int klp_write_module_reloc(struct module *mod, unsigned long
    >> - type, unsigned long loc, unsigned long value)
    >> -{
    >> - /* not supported yet */
    >> - return -ENOSYS;
    >> -}
    >> -
    >> static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
    >> {
    >> regs->psw.addr = ip;
    >> diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
    >> index e795f52..d7c2b57 100644
    >> --- a/arch/x86/include/asm/livepatch.h
    >> +++ b/arch/x86/include/asm/livepatch.h
    >> @@ -33,8 +33,6 @@ static inline int klp_check_compiler_support(void)
    >> #endif
    >> return 0;
    >> }
    >> -int klp_write_module_reloc(struct module *mod, unsigned long type,
    >> - unsigned long loc, unsigned long value);
    >>
    >> static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
    >> {
    >> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
    >> index b1b78ff..c5e9a5c 100644
    >> --- a/arch/x86/kernel/Makefile
    >> +++ b/arch/x86/kernel/Makefile
    >> @@ -67,7 +67,6 @@ obj-$(CONFIG_X86_MPPARSE) += mpparse.o
    >> obj-y += apic/
    >> obj-$(CONFIG_X86_REBOOTFIXUPS) += reboot_fixups_32.o
    >> obj-$(CONFIG_DYNAMIC_FTRACE) += ftrace.o
    >> -obj-$(CONFIG_LIVEPATCH) += livepatch.o
    >> obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
    >> obj-$(CONFIG_FTRACE_SYSCALLS) += ftrace.o
    >> obj-$(CONFIG_X86_TSC) += trace_clock.o
    >> diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c
    >> deleted file mode 100644
    >> index 92fc1a5..0000000
    >> --- a/arch/x86/kernel/livepatch.c
    >> +++ /dev/null
    >> @@ -1,70 +0,0 @@
    >> -/*
    >> - * livepatch.c - x86-specific Kernel Live Patching Core
    >> - *
    >> - * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
    >> - * Copyright (C) 2014 SUSE
    >> - *
    >> - * This program is free software; you can redistribute it and/or
    >> - * modify it under the terms of the GNU General Public License
    >> - * as published by the Free Software Foundation; either version 2
    >> - * of the License, or (at your option) any later version.
    >> - *
    >> - * This program is distributed in the hope that it will be useful,
    >> - * but WITHOUT ANY WARRANTY; without even the implied warranty of
    >> - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    >> - * GNU General Public License for more details.
    >> - *
    >> - * You should have received a copy of the GNU General Public License
    >> - * along with this program; if not, see <http://www.gnu.org/licenses/>.
    >> - */
    >> -
    >> -#include <linux/module.h>
    >> -#include <linux/uaccess.h>
    >> -#include <asm/elf.h>
    >> -#include <asm/livepatch.h>
    >> -
    >> -/**
    >> - * klp_write_module_reloc() - write a relocation in a module
    >> - * @mod: module in which the section to be modified is found
    >> - * @type: ELF relocation type (see asm/elf.h)
    >> - * @loc: address that the relocation should be written to
    >> - * @value: relocation value (sym address + addend)
    >> - *
    >> - * This function writes a relocation to the specified location for
    >> - * a particular module.
    >> - */
    >> -int klp_write_module_reloc(struct module *mod, unsigned long type,
    >> - unsigned long loc, unsigned long value)
    >> -{
    >> - size_t size = 4;
    >> - unsigned long val;
    >> - unsigned long core = (unsigned long)mod->core_layout.base;
    >> - unsigned long core_size = mod->core_layout.size;
    >> -
    >> - switch (type) {
    >> - case R_X86_64_NONE:
    >> - return 0;
    >> - case R_X86_64_64:
    >> - val = value;
    >> - size = 8;
    >> - break;
    >> - case R_X86_64_32:
    >> - val = (u32)value;
    >> - break;
    >> - case R_X86_64_32S:
    >> - val = (s32)value;
    >> - break;
    >> - case R_X86_64_PC32:
    >> - val = (u32)(value - loc);
    >> - break;
    >> - default:
    >> - /* unsupported relocation type */
    >> - return -EINVAL;
    >> - }
    >> -
    >> - if (loc < core || loc >= core + core_size)
    >> - /* loc does not point to any symbol inside the module */
    >> - return -EINVAL;
    >> -
    >> - return probe_kernel_write((void *)loc, &val, size);
    >> -}
    >> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
    >> index fdd5f1c..1a40a72 100644
    >> --- a/include/linux/livepatch.h
    >> +++ b/include/linux/livepatch.h
    >> @@ -65,27 +65,8 @@ struct klp_func {
    >> };
    >>
    >> /**
    >> - * struct klp_reloc - relocation structure for live patching
    >> - * @loc: address where the relocation will be written
    >> - * @sympos: position in kallsyms to disambiguate symbols (optional)
    >> - * @type: ELF relocation type
    >> - * @name: name of the referenced symbol (for lookup/verification)
    >> - * @addend: offset from the referenced symbol
    >> - * @external: symbol is either exported or within the live patch module itself
    >> - */
    >> -struct klp_reloc {
    >> - unsigned long loc;
    >> - unsigned long sympos;
    >> - unsigned long type;
    >> - const char *name;
    >> - int addend;
    >> - int external;
    >> -};
    >> -
    >> -/**
    >> * struct klp_object - kernel object structure for live patching
    >> * @name: module name (or NULL for vmlinux)
    >> - * @relocs: relocation entries to be applied at load time
    >> * @funcs: function entries for functions to be patched in the object
    >> * @kobj: kobject for sysfs resources
    >> * @mod: kernel module associated with the patched object
    >> @@ -95,7 +76,6 @@ struct klp_reloc {
    >> struct klp_object {
    >> /* external */
    >> const char *name;
    >> - struct klp_reloc *relocs;
    >> struct klp_func *funcs;
    >>
    >> /* internal */
    >> @@ -123,6 +103,16 @@ struct klp_patch {
    >> enum klp_state state;
    >> };
    >>
    >> +/*
    >> + * Livepatch symbol and relocation section prefixes:
    >> + * ".klp.rela." for relocation sections
    >> + * ".klp.sym." for livepatch symbols
    >> + */
    >> +#define KLP_SYM_PREFIX ".klp.sym."
    >> +#define KLP_SYM_PREFIX_LEN 9
    >> +#define KLP_RELASEC_PREFIX ".klp.rela."
    >> +#define KLP_RELASEC_PREFIX_LEN 10
    >> +
    >> #define klp_for_each_object(patch, obj) \
    >> for (obj = patch->objs; obj->funcs; obj++)
    >>
    >> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
    >> index 7aa975d..c1fe57c 100644
    >> --- a/kernel/livepatch/core.c
    >> +++ b/kernel/livepatch/core.c
    >> @@ -28,6 +28,9 @@
    >> #include <linux/list.h>
    >> #include <linux/kallsyms.h>
    >> #include <linux/livepatch.h>
    >> +#include <linux/elf.h>
    >> +#include <linux/string.h>
    >> +#include <linux/moduleloader.h>
    >> #include <asm/cacheflush.h>
    >>
    >> /**
    >> @@ -87,6 +90,166 @@ static bool klp_is_object_loaded(struct klp_object *obj)
    >> return !obj->name || obj->mod;
    >> }
    >>
    >> +/*
    >> + * Check if a livepatch symbol is formatted properly.
    >> + *
    >> + * See Documentation/livepatch/module-elf-format.txt for a
    >> + * detailed outline of requirements.
    >> + */
    >> +static int klp_check_symbol_format(struct module *pmod, Elf_Sym *sym)
    >> +{
    >> + size_t len;
    >> + char *s, *objname, *symname;
    >> +
    >> + if (sym->st_shndx != SHN_LIVEPATCH)
    >> + return -EINVAL;
    >> +
    >> + /*
    >> + * Livepatch symbol names must follow this format:
    >> + * .klp.sym.objname.symbol_name,sympos
    >> + */
    >> + s = pmod->strtab + sym->st_name;
    >> + /* [.klp.sym.]objname.symbol_name,sympos */
    >> + if (!s || strncmp(s, KLP_SYM_PREFIX, KLP_SYM_PREFIX_LEN))
    >> + return -EINVAL;
    >> +
    >> + /* .klp.sym.[objname].symbol_name,sympos */
    >> + objname = s + KLP_SYM_PREFIX_LEN;
    >> + len = strcspn(objname, ".");
    >> + if (!(len > 0))
    >> + return -EINVAL;
    >> +
    >> + /* .klp.sym.objname.symbol_name,[sympos] */
    >> + if (!strchr(s, ','))
    >> + return -EINVAL;
    >> +
    >> + /* .klp.sym.objname.[symbol_name],sympos */
    >> + symname = objname + len + 1;
    >> + len = strcspn(symname, ",");
    >> + if (!(len > 0))
    >> + return -EINVAL;
    >> +
    >> + return 0;
    >> +}
    >> +
    >> +/*
    >> + * Check if a livepatch relocation section is formatted properly.
    >> + *
    >> + * See Documentation/livepatch/module-elf-format.txt for a
    >> + * detailed outline of requirements.
    >> + */
    >> +static int klp_check_relasec_format(struct module *pmod, Elf_Shdr *relasec)
    >> +{
    >> + char *secname;
    >> + size_t len;
    >> +
    >> + secname = pmod->klp_info->secstrings + relasec->sh_name;
    >> + /* [.klp.rela.]objname.section_name */
    >> + if (!secname || strncmp(secname, KLP_RELASEC_PREFIX,
    >> + KLP_RELASEC_PREFIX_LEN))
    >> + return -EINVAL;
    >> +
    >> + /* .klp.rela.[objname].section_name */
    >> + len = strcspn(secname + KLP_RELASEC_PREFIX_LEN, ".");
    >> + if (!(len > 0))
    >> + return -EINVAL;
    >> +
    >> + return 0;
    >> +}
    >> +
    >> +/*
    >> + * Check if obj->name matches the objname encoded in the rela
    >> + * section name (.klp.rela.[objname].section_name)
    >> + *
    >> + * Must pass klp_check_relasec_format() before calling this.
    >> + */
    >> +static bool klp_relasec_matches_object(struct module *pmod, Elf_Shdr *relasec,
    >> + struct klp_object *obj)
    >> +{
    >> + size_t len;
    >> + const char *obj_objname, *sec_objname, *secname;
    >> +
    >> + secname = pmod->klp_info->secstrings + relasec->sh_name;
    >> + /* .klp.rela.[objname].section_name */
    >> + sec_objname = secname + KLP_RELASEC_PREFIX_LEN;
    >> + obj_objname = klp_is_module(obj) ? obj->name : "vmlinux";
    >> +
    >> + /* Get length of the objname encoded in the section name */
    >> + len = strcspn(sec_objname, ".");
    >> +
    >> + if (strlen(obj_objname) != len)
    >> + return false;
    >> +
    >> + return strncmp(sec_objname, obj_objname, len) ? false : true;
    >> +}
    >> +
    >> +/*
    >> + * klp_get_* helper functions
    >> + *
    >> + * klp_get_* functions extract different components of the name
    >> + * of a livepatch symbol. The full symbol name from the strtab
    >> + * is passed in as parameter @s, and @result is filled in with
    >> + * the extracted component.
    >> + *
    >> + * These functions assume a correctly formatted symbol and the
    >> + * klp_check_symbol_format() test *must* pass before calling any
    >> + * of these functions.
    >> + */
    >> +
    >> +/* .klp.sym.[objname].symbol_name,sympos */
    >> +static int klp_get_sym_objname(char *s, char **result)
    >> +{
    >> + size_t len;
    >> + char *objname, *objname_start;
    >> +
    >> + /* .klp.sym.[objname].symbol_name,sympos */
    >> + objname_start = s + KLP_SYM_PREFIX_LEN;
    >> + len = strcspn(objname_start, ".");
    >> + objname = kstrndup(objname_start, len, GFP_KERNEL);
    >> + if (objname == NULL)
    >> + return -ENOMEM;
    >> +
    >> + /* klp_find_object_symbol() treats NULL as vmlinux */
    >> + if (!strcmp(objname, "vmlinux")) {
    >> + *result = NULL;
    >> + kfree(objname);
    >> + } else
    >> + *result = objname;
    >> +
    >> + return 0;
    >> +}
    >> +
    >> +/* .klp.sym.objname.[symbol_name],sympos */
    >> +static int klp_get_symbol_name(char *s, char **result)
    >> +{
    >> + size_t len;
    >> + char *objname, *symname;
    >> +
    >> + /* .klp.sym.[objname].symbol_name,sympos */
    >> + objname = s + KLP_SYM_PREFIX_LEN;
    >> + len = strcspn(objname, ".");
    >> +
    >> + /* .klp.sym.objname.[symbol_name],sympos */
    >> + symname = objname + len + 1;
    >> + len = strcspn(symname, ",");
    >> +
    >> + *result = kstrndup(symname, len, GFP_KERNEL);
    >> + if (*result == NULL)
    >> + return -ENOMEM;
    >> +
    >> + return 0;
    >> +}
    >> +
    >> +/* .klp.sym.objname.symbol_name,[sympos] */
    >> +static int klp_get_sympos(char *s, unsigned long *result)
    >> +{
    >> + char *sympos;
    >> +
    >> + /* .klp.sym.symbol_name,[sympos] */
    >> + sympos = strchr(s, ',') + 1;
    >> + return kstrtol(sympos, 10, result);
    >> +}
    >> +
    >> /* sets obj->mod if object is not vmlinux and module is found */
    >> static void klp_find_object_module(struct klp_object *obj)
    >> {
    >
    >I think all the above string parsing code could be replaced with a
    >couple of sscanf() calls.
    >
    >For example:
    >
    > char objname[64], symname[256];
    >
    > ret = sscanf(s, ".klp.sym.%63[^.].%255[^,],%u", objname, symname, &sympos);
    > if (ret < 3)
    > // string doesn't match expected format
    >
    >That would be much simpler.
    >
    >Only problem is, the kernel version of sscanf() doesn't seem to support
    >the '[' conversion specifier. At least not yet ;-) Adding support for
    >that would be a win-win: less code overall, and the addition of a useful
    >scanf feature which could be used by other code.

    Ah, I had completely forgotten that we have sscanf() in the kernel :-)
    That would look *much* nicer, assuming we can get kernel sscanf() to
    support the bracket character classes..

    Jessica

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