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module: clean up RO/NX handling.
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Modules have three sections: text, rodata and writable data.  The code
handled the case where these overlapped, however they never can:
debug_align() ensures they are always page-aligned.

This is why we got away with manually traversing the pages in
set_all_modules_text_rw() without rounding.

We create three helper functions: frob_text(), frob_rodata() and
frob_writable_data().  We then call these explicitly at every point,
so it's clear what we're doing.

We also expose module_enable_ro() and module_disable_ro() for
livepatch to use.

Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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@rustyrussell
rustyrussell authored and Jiri Kosina committed Dec 4, 2015
1 parent 7523e4d commit 85c898d
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Showing 2 changed files with 81 additions and 91 deletions.
4 changes: 4 additions & 0 deletions include/linux/module.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -762,9 +762,13 @@ 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_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_disable_ro(const struct module *mod) { }
#endif

#ifdef CONFIG_GENERIC_BUG
Expand Down
168 changes: 77 additions & 91 deletions kernel/module.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -80,15 +80,6 @@
# define debug_align(X) (X)
#endif

/*
* Given BASE and SIZE this macro calculates the number of pages the
* memory regions occupies
*/
#define MOD_NUMBER_OF_PAGES(BASE, SIZE) (((SIZE) > 0) ? \
(PFN_DOWN((unsigned long)(BASE) + (SIZE) - 1) - \
PFN_DOWN((unsigned long)BASE) + 1) \
: (0UL))

/* If this is set, the section belongs in the init part of the module */
#define INIT_OFFSET_MASK (1UL << (BITS_PER_LONG-1))

Expand Down Expand Up @@ -1858,74 +1849,75 @@ static void mod_sysfs_teardown(struct module *mod)
/*
* LKM RO/NX protection: protect module's text/ro-data
* from modification and any data from execution.
*
* General layout of module is:
* [text] [read-only-data] [writable data]
* text_size -----^ ^ ^
* ro_size ------------------------| |
* size -------------------------------------------|
*
* These values are always page-aligned (as is base)
*/
void set_page_attributes(void *start, void *end, int (*set)(unsigned long start, int num_pages))
static void frob_text(const struct module_layout *layout,
int (*set_memory)(unsigned long start, int num_pages))
{
unsigned long begin_pfn = PFN_DOWN((unsigned long)start);
unsigned long end_pfn = PFN_DOWN((unsigned long)end);

if (end_pfn > begin_pfn)
set(begin_pfn << PAGE_SHIFT, end_pfn - begin_pfn);
BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->text_size & (PAGE_SIZE-1));
set_memory((unsigned long)layout->base,
layout->text_size >> PAGE_SHIFT);
}

static void set_section_ro_nx(void *base,
unsigned long text_size,
unsigned long ro_size,
unsigned long total_size,
int (*set_ro)(unsigned long start, int num_pages),
int (*set_nx)(unsigned long start, int num_pages))
static void frob_rodata(const struct module_layout *layout,
int (*set_memory)(unsigned long start, int num_pages))
{
/* begin and end PFNs of the current subsection */
unsigned long begin_pfn;
unsigned long end_pfn;

/*
* Set RO for module text and RO-data:
* - Always protect first page.
* - Do not protect last partial page.
*/
if (ro_size > 0)
set_page_attributes(base, base + ro_size, set_ro);
BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->text_size & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->ro_size & (PAGE_SIZE-1));
set_memory((unsigned long)layout->base + layout->text_size,
(layout->ro_size - layout->text_size) >> PAGE_SHIFT);
}

/*
* Set NX permissions for module data:
* - Do not protect first partial page.
* - Always protect last page.
*/
if (total_size > text_size) {
begin_pfn = PFN_UP((unsigned long)base + text_size);
end_pfn = PFN_UP((unsigned long)base + total_size);
if (end_pfn > begin_pfn)
set_nx(begin_pfn << PAGE_SHIFT, end_pfn - begin_pfn);
}
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->size & (PAGE_SIZE-1));
set_memory((unsigned long)layout->base + layout->ro_size,
(layout->size - layout->ro_size) >> PAGE_SHIFT);
}

static void set_module_core_ro_nx(struct module *mod)
/* livepatching wants to disable read-only so it can frob module. */
void module_disable_ro(const struct module *mod)
{
set_section_ro_nx(mod->core_layout.base, mod->core_layout.text_size,
mod->core_layout.ro_size, mod->core_layout.size,
set_memory_ro, set_memory_nx);
frob_text(&mod->core_layout, set_memory_rw);
frob_rodata(&mod->core_layout, set_memory_rw);
frob_text(&mod->init_layout, set_memory_rw);
frob_rodata(&mod->init_layout, set_memory_rw);
}

static void unset_module_core_ro_nx(struct module *mod)
void module_enable_ro(const struct module *mod)
{
set_section_ro_nx(mod->core_layout.base, mod->core_layout.text_size,
mod->core_layout.ro_size, mod->core_layout.size,
set_memory_rw, set_memory_x);
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);
}

static void set_module_init_ro_nx(struct module *mod)
static void module_enable_nx(const struct module *mod)
{
set_section_ro_nx(mod->init_layout.base, mod->init_layout.text_size,
mod->init_layout.ro_size, mod->init_layout.size,
set_memory_ro, set_memory_nx);
frob_rodata(&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);
}

static void unset_module_init_ro_nx(struct module *mod)
static void module_disable_nx(const struct module *mod)
{
set_section_ro_nx(mod->init_layout.base, mod->init_layout.text_size,
mod->init_layout.ro_size, mod->init_layout.size,
set_memory_rw, set_memory_x);
frob_rodata(&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);
}

/* Iterate through all modules and set each module's text as RW */
Expand All @@ -1937,16 +1929,9 @@ void set_all_modules_text_rw(void)
list_for_each_entry_rcu(mod, &modules, list) {
if (mod->state == MODULE_STATE_UNFORMED)
continue;
if ((mod->core_layout.base) && (mod->core_layout.text_size)) {
set_page_attributes(mod->core_layout.base,
mod->core_layout.base + mod->core_layout.text_size,
set_memory_rw);
}
if ((mod->init_layout.base) && (mod->init_layout.text_size)) {
set_page_attributes(mod->init_layout.base,
mod->init_layout.base + mod->init_layout.text_size,
set_memory_rw);
}

frob_text(&mod->core_layout, set_memory_rw);
frob_text(&mod->init_layout, set_memory_rw);
}
mutex_unlock(&module_mutex);
}
Expand All @@ -1960,24 +1945,25 @@ void set_all_modules_text_ro(void)
list_for_each_entry_rcu(mod, &modules, list) {
if (mod->state == MODULE_STATE_UNFORMED)
continue;
if ((mod->core_layout.base) && (mod->core_layout.text_size)) {
set_page_attributes(mod->core_layout.base,
mod->core_layout.base + mod->core_layout.text_size,
set_memory_ro);
}
if ((mod->init_layout.base) && (mod->init_layout.text_size)) {
set_page_attributes(mod->init_layout.base,
mod->init_layout.base + mod->init_layout.text_size,
set_memory_ro);
}

frob_text(&mod->core_layout, set_memory_ro);
frob_text(&mod->init_layout, set_memory_ro);
}
mutex_unlock(&module_mutex);
}

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_writable_data(layout, set_memory_x);
}

#else
static void set_module_core_ro_nx(struct module *mod) { }
static void set_module_init_ro_nx(struct module *mod) { }
static void unset_module_core_ro_nx(struct module *mod) { }
static void unset_module_init_ro_nx(struct module *mod) { }
static void disable_ro_nx(const struct module_layout *layout) { }
static void module_enable_nx(const struct module *mod) { }
static void module_disable_nx(const struct module *mod) { }
#endif

void __weak module_memfree(void *module_region)
Expand Down Expand Up @@ -2029,8 +2015,8 @@ static void free_module(struct module *mod)
synchronize_sched();
mutex_unlock(&module_mutex);

/* This may be NULL, but that's OK */
unset_module_init_ro_nx(mod);
/* This may be empty, but that's OK */
disable_ro_nx(&mod->init_layout);
module_arch_freeing_init(mod);
module_memfree(mod->init_layout.base);
kfree(mod->args);
Expand All @@ -2040,7 +2026,7 @@ static void free_module(struct module *mod)
lockdep_free_key_range(mod->core_layout.base, mod->core_layout.size);

/* Finally, free the core (containing the module structure) */
unset_module_core_ro_nx(mod);
disable_ro_nx(&mod->core_layout);
module_memfree(mod->core_layout.base);

#ifdef CONFIG_MPU
Expand Down Expand Up @@ -3275,7 +3261,7 @@ static noinline int do_init_module(struct module *mod)
mod->strtab = mod->core_strtab;
#endif
mod_tree_remove_init(mod);
unset_module_init_ro_nx(mod);
disable_ro_nx(&mod->init_layout);
module_arch_freeing_init(mod);
mod->init_layout.base = NULL;
mod->init_layout.size = 0;
Expand Down Expand Up @@ -3370,8 +3356,8 @@ static int complete_formation(struct module *mod, struct load_info *info)
module_bug_finalize(info->hdr, info->sechdrs, mod);

/* Set RO and NX regions */
set_module_init_ro_nx(mod);
set_module_core_ro_nx(mod);
module_enable_ro(mod);
module_enable_nx(mod);

/* Mark state as coming so strong_try_module_get() ignores us,
* but kallsyms etc. can see us. */
Expand Down Expand Up @@ -3536,8 +3522,8 @@ static int load_module(struct load_info *info, const char __user *uargs,
MODULE_STATE_GOING, mod);

/* we can't deallocate the module until we clear memory protection */
unset_module_init_ro_nx(mod);
unset_module_core_ro_nx(mod);
module_disable_ro(mod);
module_disable_nx(mod);

ddebug_cleanup:
dynamic_debug_remove(info->debug);
Expand Down

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