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modules: add ro_after_init support
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Add ro_after_init support for modules by adding a new page-aligned section
in the module layout (after rodata) for ro_after_init data and enabling RO
protection for that section after module init runs.

Signed-off-by: Jessica Yu <[email protected]>
Acked-by: Kees Cook <[email protected]>
Signed-off-by: Rusty Russell <[email protected]>
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@rustyrussell
Jessica Yu authored and rustyrussell committed Aug 4, 2016
1 parent bdc9f37 commit 444d13f
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Showing 4 changed files with 60 additions and 15 deletions.
6 changes: 4 additions & 2 deletions include/linux/module.h
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Original file line number Diff line number Diff line change
Expand Up @@ -298,6 +298,8 @@ struct module_layout {
unsigned int text_size;
/* Size of RO section of the module (text+rodata) */
unsigned int ro_size;
/* Size of RO after init section */
unsigned int ro_after_init_size;

#ifdef CONFIG_MODULES_TREE_LOOKUP
struct mod_tree_node mtn;
Expand Down Expand Up @@ -765,12 +767,12 @@ extern int module_sysfs_initialized;
#ifdef CONFIG_DEBUG_SET_MODULE_RONX
extern void set_all_modules_text_rw(void);
extern void set_all_modules_text_ro(void);
extern void module_enable_ro(const struct module *mod);
extern void module_enable_ro(const struct module *mod, bool after_init);
extern void module_disable_ro(const struct module *mod);
#else
static inline void set_all_modules_text_rw(void) { }
static inline void set_all_modules_text_ro(void) { }
static inline void module_enable_ro(const struct module *mod) { }
static inline void module_enable_ro(const struct module *mod, bool after_init) { }
static inline void module_disable_ro(const struct module *mod) { }
#endif

Expand Down
1 change: 1 addition & 0 deletions include/uapi/linux/elf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -286,6 +286,7 @@ typedef struct elf64_phdr {
#define SHF_ALLOC 0x2
#define SHF_EXECINSTR 0x4
#define SHF_RELA_LIVEPATCH 0x00100000
#define SHF_RO_AFTER_INIT 0x00200000
#define SHF_MASKPROC 0xf0000000

/* special section indexes */
Expand Down
2 changes: 1 addition & 1 deletion kernel/livepatch/core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -309,7 +309,7 @@ static int klp_write_object_relocations(struct module *pmod,
break;
}

module_enable_ro(pmod);
module_enable_ro(pmod, true);
return ret;
}

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66 changes: 54 additions & 12 deletions kernel/module.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1857,10 +1857,11 @@ static void mod_sysfs_teardown(struct module *mod)
* from modification and any data from execution.
*
* General layout of module is:
* [text] [read-only-data] [writable data]
* text_size -----^ ^ ^
* ro_size ------------------------| |
* size -------------------------------------------|
* [text] [read-only-data] [ro-after-init] [writable data]
* text_size -----^ ^ ^ ^
* ro_size ------------------------| | |
* ro_after_init_size -----------------------------| |
* size -----------------------------------------------------------|
*
* These values are always page-aligned (as is base)
*/
Expand All @@ -1883,36 +1884,51 @@ static void frob_rodata(const struct module_layout *layout,
(layout->ro_size - layout->text_size) >> PAGE_SHIFT);
}

static void frob_ro_after_init(const struct module_layout *layout,
int (*set_memory)(unsigned long start, int num_pages))
{
BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->ro_size & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->ro_after_init_size & (PAGE_SIZE-1));
set_memory((unsigned long)layout->base + layout->ro_size,
(layout->ro_after_init_size - layout->ro_size) >> PAGE_SHIFT);
}

static void frob_writable_data(const struct module_layout *layout,
int (*set_memory)(unsigned long start, int num_pages))
{
BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->ro_size & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->ro_after_init_size & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->size & (PAGE_SIZE-1));
set_memory((unsigned long)layout->base + layout->ro_size,
(layout->size - layout->ro_size) >> PAGE_SHIFT);
set_memory((unsigned long)layout->base + layout->ro_after_init_size,
(layout->size - layout->ro_after_init_size) >> PAGE_SHIFT);
}

/* livepatching wants to disable read-only so it can frob module. */
void module_disable_ro(const struct module *mod)
{
frob_text(&mod->core_layout, set_memory_rw);
frob_rodata(&mod->core_layout, set_memory_rw);
frob_ro_after_init(&mod->core_layout, set_memory_rw);
frob_text(&mod->init_layout, set_memory_rw);
frob_rodata(&mod->init_layout, set_memory_rw);
}

void module_enable_ro(const struct module *mod)
void module_enable_ro(const struct module *mod, bool after_init)
{
frob_text(&mod->core_layout, set_memory_ro);
frob_rodata(&mod->core_layout, set_memory_ro);
frob_text(&mod->init_layout, set_memory_ro);
frob_rodata(&mod->init_layout, set_memory_ro);

if (after_init)
frob_ro_after_init(&mod->core_layout, set_memory_ro);
}

static void module_enable_nx(const struct module *mod)
{
frob_rodata(&mod->core_layout, set_memory_nx);
frob_ro_after_init(&mod->core_layout, set_memory_nx);
frob_writable_data(&mod->core_layout, set_memory_nx);
frob_rodata(&mod->init_layout, set_memory_nx);
frob_writable_data(&mod->init_layout, set_memory_nx);
Expand All @@ -1921,6 +1937,7 @@ static void module_enable_nx(const struct module *mod)
static void module_disable_nx(const struct module *mod)
{
frob_rodata(&mod->core_layout, set_memory_x);
frob_ro_after_init(&mod->core_layout, set_memory_x);
frob_writable_data(&mod->core_layout, set_memory_x);
frob_rodata(&mod->init_layout, set_memory_x);
frob_writable_data(&mod->init_layout, set_memory_x);
Expand Down Expand Up @@ -1963,6 +1980,8 @@ static void disable_ro_nx(const struct module_layout *layout)
frob_text(layout, set_memory_rw);
frob_rodata(layout, set_memory_rw);
frob_rodata(layout, set_memory_x);
frob_ro_after_init(layout, set_memory_rw);
frob_ro_after_init(layout, set_memory_x);
frob_writable_data(layout, set_memory_x);
}

Expand Down Expand Up @@ -2305,6 +2324,7 @@ static void layout_sections(struct module *mod, struct load_info *info)
* finder in the two loops below */
{ SHF_EXECINSTR | SHF_ALLOC, ARCH_SHF_SMALL },
{ SHF_ALLOC, SHF_WRITE | ARCH_SHF_SMALL },
{ SHF_RO_AFTER_INIT | SHF_ALLOC, ARCH_SHF_SMALL },
{ SHF_WRITE | SHF_ALLOC, ARCH_SHF_SMALL },
{ ARCH_SHF_SMALL | SHF_ALLOC, 0 }
};
Expand Down Expand Up @@ -2336,7 +2356,11 @@ static void layout_sections(struct module *mod, struct load_info *info)
mod->core_layout.size = debug_align(mod->core_layout.size);
mod->core_layout.ro_size = mod->core_layout.size;
break;
case 3: /* whole core */
case 2: /* RO after init */
mod->core_layout.size = debug_align(mod->core_layout.size);
mod->core_layout.ro_after_init_size = mod->core_layout.size;
break;
case 4: /* whole core */
mod->core_layout.size = debug_align(mod->core_layout.size);
break;
}
Expand Down Expand Up @@ -2366,7 +2390,14 @@ static void layout_sections(struct module *mod, struct load_info *info)
mod->init_layout.size = debug_align(mod->init_layout.size);
mod->init_layout.ro_size = mod->init_layout.size;
break;
case 3: /* whole init */
case 2:
/*
* RO after init doesn't apply to init_layout (only
* core_layout), so it just takes the value of ro_size.
*/
mod->init_layout.ro_after_init_size = mod->init_layout.ro_size;
break;
case 4: /* whole init */
mod->init_layout.size = debug_align(mod->init_layout.size);
break;
}
Expand Down Expand Up @@ -3193,6 +3224,7 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
{
/* Module within temporary copy. */
struct module *mod;
unsigned int ndx;
int err;

mod = setup_load_info(info, flags);
Expand All @@ -3215,6 +3247,15 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
/* We will do a special allocation for per-cpu sections later. */
info->sechdrs[info->index.pcpu].sh_flags &= ~(unsigned long)SHF_ALLOC;

/*
* Mark ro_after_init section with SHF_RO_AFTER_INIT so that
* layout_sections() can put it in the right place.
* Note: ro_after_init sections also have SHF_{WRITE,ALLOC} set.
*/
ndx = find_sec(info, ".data..ro_after_init");
if (ndx)
info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT;

/* Determine total sizes, and put offsets in sh_entsize. For now
this is done generically; there doesn't appear to be any
special cases for the architectures. */
Expand Down Expand Up @@ -3381,12 +3422,14 @@ static noinline int do_init_module(struct module *mod)
/* Switch to core kallsyms now init is done: kallsyms may be walking! */
rcu_assign_pointer(mod->kallsyms, &mod->core_kallsyms);
#endif
module_enable_ro(mod, true);
mod_tree_remove_init(mod);
disable_ro_nx(&mod->init_layout);
module_arch_freeing_init(mod);
mod->init_layout.base = NULL;
mod->init_layout.size = 0;
mod->init_layout.ro_size = 0;
mod->init_layout.ro_after_init_size = 0;
mod->init_layout.text_size = 0;
/*
* We want to free module_init, but be aware that kallsyms may be
Expand Down Expand Up @@ -3478,8 +3521,7 @@ static int complete_formation(struct module *mod, struct load_info *info)
/* This relies on module_mutex for list integrity. */
module_bug_finalize(info->hdr, info->sechdrs, mod);

/* Set RO and NX regions */
module_enable_ro(mod);
module_enable_ro(mod, false);
module_enable_nx(mod);

/* Mark state as coming so strong_try_module_get() ignores us,
Expand Down

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