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Merge tag 'livepatching-for-6.3' of git://git.kernel.org/pub/scm/linu…
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…x/kernel/git/livepatching/livepatching

Pull livepatching updates from Petr Mladek:

 - Allow reloading a livepatched module by clearing livepatch-specific
   relocations in the livepatch module.

   Otherwise, the repeated load would fail on consistency checks.

* tag 'livepatching-for-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/livepatching/livepatching:
  livepatch,x86: Clear relocation targets on a module removal
  x86/module: remove unused code in __apply_relocate_add
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Linus Torvalds committed Feb 23, 2023
2 parents d876315 + 0c05e7b commit 7dd86cf
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Showing 3 changed files with 126 additions and 50 deletions.
97 changes: 60 additions & 37 deletions arch/x86/kernel/module.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -129,22 +129,27 @@ int apply_relocate(Elf32_Shdr *sechdrs,
return 0;
}
#else /*X86_64*/
static int __apply_relocate_add(Elf64_Shdr *sechdrs,
static int __write_relocate_add(Elf64_Shdr *sechdrs,
const char *strtab,
unsigned int symindex,
unsigned int relsec,
struct module *me,
void *(*write)(void *dest, const void *src, size_t len))
void *(*write)(void *dest, const void *src, size_t len),
bool apply)
{
unsigned int i;
Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
Elf64_Sym *sym;
void *loc;
u64 val;
u64 zero = 0ULL;

DEBUGP("Applying relocate section %u to %u\n",
DEBUGP("%s relocate section %u to %u\n",
apply ? "Applying" : "Clearing",
relsec, sechdrs[relsec].sh_info);
for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
size_t size;

/* This is where to make the change */
loc = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
+ rel[i].r_offset;
Expand All @@ -162,56 +167,53 @@ static int __apply_relocate_add(Elf64_Shdr *sechdrs,

switch (ELF64_R_TYPE(rel[i].r_info)) {
case R_X86_64_NONE:
break;
continue; /* nothing to write */
case R_X86_64_64:
if (*(u64 *)loc != 0)
goto invalid_relocation;
write(loc, &val, 8);
size = 8;
break;
case R_X86_64_32:
if (*(u32 *)loc != 0)
goto invalid_relocation;
write(loc, &val, 4);
if (val != *(u32 *)loc)
if (val != *(u32 *)&val)
goto overflow;
size = 4;
break;
case R_X86_64_32S:
if (*(s32 *)loc != 0)
goto invalid_relocation;
write(loc, &val, 4);
if ((s64)val != *(s32 *)loc)
if ((s64)val != *(s32 *)&val)
goto overflow;
size = 4;
break;
case R_X86_64_PC32:
case R_X86_64_PLT32:
if (*(u32 *)loc != 0)
goto invalid_relocation;
val -= (u64)loc;
write(loc, &val, 4);
#if 0
if ((s64)val != *(s32 *)loc)
goto overflow;
#endif
size = 4;
break;
case R_X86_64_PC64:
if (*(u64 *)loc != 0)
goto invalid_relocation;
val -= (u64)loc;
write(loc, &val, 8);
size = 8;
break;
default:
pr_err("%s: Unknown rela relocation: %llu\n",
me->name, ELF64_R_TYPE(rel[i].r_info));
return -ENOEXEC;
}

if (apply) {
if (memcmp(loc, &zero, size)) {
pr_err("x86/modules: Invalid relocation target, existing value is nonzero for type %d, loc %p, val %Lx\n",
(int)ELF64_R_TYPE(rel[i].r_info), loc, val);
return -ENOEXEC;
}
write(loc, &val, size);
} else {
if (memcmp(loc, &val, size)) {
pr_warn("x86/modules: Invalid relocation target, existing value does not match expected value for type %d, loc %p, val %Lx\n",
(int)ELF64_R_TYPE(rel[i].r_info), loc, val);
return -ENOEXEC;
}
write(loc, &zero, size);
}
}
return 0;

invalid_relocation:
pr_err("x86/modules: Skipping invalid relocation target, existing value is nonzero for type %d, loc %p, val %Lx\n",
(int)ELF64_R_TYPE(rel[i].r_info), loc, val);
return -ENOEXEC;

overflow:
pr_err("overflow in relocation type %d val %Lx\n",
(int)ELF64_R_TYPE(rel[i].r_info), val);
Expand All @@ -220,11 +222,12 @@ static int __apply_relocate_add(Elf64_Shdr *sechdrs,
return -ENOEXEC;
}

int apply_relocate_add(Elf64_Shdr *sechdrs,
const char *strtab,
unsigned int symindex,
unsigned int relsec,
struct module *me)
static int write_relocate_add(Elf64_Shdr *sechdrs,
const char *strtab,
unsigned int symindex,
unsigned int relsec,
struct module *me,
bool apply)
{
int ret;
bool early = me->state == MODULE_STATE_UNFORMED;
Expand All @@ -235,8 +238,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
mutex_lock(&text_mutex);
}

ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
write);
ret = __write_relocate_add(sechdrs, strtab, symindex, relsec, me,
write, apply);

if (!early) {
text_poke_sync();
Expand All @@ -246,6 +249,26 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
return ret;
}

int apply_relocate_add(Elf64_Shdr *sechdrs,
const char *strtab,
unsigned int symindex,
unsigned int relsec,
struct module *me)
{
return write_relocate_add(sechdrs, strtab, symindex, relsec, me, true);
}

#ifdef CONFIG_LIVEPATCH
void clear_relocate_add(Elf64_Shdr *sechdrs,
const char *strtab,
unsigned int symindex,
unsigned int relsec,
struct module *me)
{
write_relocate_add(sechdrs, strtab, symindex, relsec, me, false);
}
#endif

#endif

int module_finalize(const Elf_Ehdr *hdr,
Expand Down
17 changes: 17 additions & 0 deletions include/linux/moduleloader.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -75,6 +75,23 @@ int apply_relocate_add(Elf_Shdr *sechdrs,
unsigned int symindex,
unsigned int relsec,
struct module *mod);
#ifdef CONFIG_LIVEPATCH
/*
* Some architectures (namely x86_64 and ppc64) perform sanity checks when
* applying relocations. If a patched module gets unloaded and then later
* reloaded (and re-patched), klp re-applies relocations to the replacement
* function(s). Any leftover relocations from the previous loading of the
* patched module might trigger the sanity checks.
*
* To prevent that, when unloading a patched module, clear out any relocations
* that might trigger arch-specific sanity checks on a future module reload.
*/
void clear_relocate_add(Elf_Shdr *sechdrs,
const char *strtab,
unsigned int symindex,
unsigned int relsec,
struct module *me);
#endif
#else
static inline int apply_relocate_add(Elf_Shdr *sechdrs,
const char *strtab,
Expand Down
62 changes: 49 additions & 13 deletions kernel/livepatch/core.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -260,6 +260,14 @@ static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
return 0;
}

void __weak clear_relocate_add(Elf_Shdr *sechdrs,
const char *strtab,
unsigned int symindex,
unsigned int relsec,
struct module *me)
{
}

/*
* At a high-level, there are two types of klp relocation sections: those which
* reference symbols which live in vmlinux; and those which reference symbols
Expand All @@ -283,10 +291,10 @@ static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
* the to-be-patched module to be loaded and patched sometime *after* the
* klp module is loaded.
*/
int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
const char *shstrtab, const char *strtab,
unsigned int symndx, unsigned int secndx,
const char *objname)
static int klp_write_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
const char *shstrtab, const char *strtab,
unsigned int symndx, unsigned int secndx,
const char *objname, bool apply)
{
int cnt, ret;
char sec_objname[MODULE_NAME_LEN];
Expand All @@ -308,11 +316,26 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
if (strcmp(objname ? objname : "vmlinux", sec_objname))
return 0;

ret = klp_resolve_symbols(sechdrs, strtab, symndx, sec, sec_objname);
if (ret)
return ret;
if (apply) {
ret = klp_resolve_symbols(sechdrs, strtab, symndx,
sec, sec_objname);
if (ret)
return ret;

return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
}

clear_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
return 0;
}

return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
const char *shstrtab, const char *strtab,
unsigned int symndx, unsigned int secndx,
const char *objname)
{
return klp_write_section_relocs(pmod, sechdrs, shstrtab, strtab, symndx,
secndx, objname, true);
}

/*
Expand Down Expand Up @@ -761,8 +784,9 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
func->old_sympos ? func->old_sympos : 1);
}

static int klp_apply_object_relocs(struct klp_patch *patch,
struct klp_object *obj)
static int klp_write_object_relocs(struct klp_patch *patch,
struct klp_object *obj,
bool apply)
{
int i, ret;
struct klp_modinfo *info = patch->mod->klp_info;
Expand All @@ -773,17 +797,29 @@ static int klp_apply_object_relocs(struct klp_patch *patch,
if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
continue;

ret = klp_apply_section_relocs(patch->mod, info->sechdrs,
ret = klp_write_section_relocs(patch->mod, info->sechdrs,
info->secstrings,
patch->mod->core_kallsyms.strtab,
info->symndx, i, obj->name);
info->symndx, i, obj->name, apply);
if (ret)
return ret;
}

return 0;
}

static int klp_apply_object_relocs(struct klp_patch *patch,
struct klp_object *obj)
{
return klp_write_object_relocs(patch, obj, true);
}

static void klp_clear_object_relocs(struct klp_patch *patch,
struct klp_object *obj)
{
klp_write_object_relocs(patch, obj, false);
}

/* parts of the initialization that is done only when the object is loaded */
static int klp_init_object_loaded(struct klp_patch *patch,
struct klp_object *obj)
Expand Down Expand Up @@ -1171,7 +1207,7 @@ static void klp_cleanup_module_patches_limited(struct module *mod,
klp_unpatch_object(obj);

klp_post_unpatch_callback(obj);

klp_clear_object_relocs(patch, obj);
klp_free_object_loaded(obj);
break;
}
Expand Down

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