[PATCH v3 3/4] module: Rework layout alignment to avoid BUG_ON()s

Christophe Leroy
2022-02-22T15:17:10Z

Perform layout alignment verification up front and WARN_ON()
and fail module loading instead of crashing the machine.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
kernel/module/internal.h | 1 +
kernel/module/main.c | 5 +++++
kernel/module/strict_rwx.c | 28 +++++++++++++++++++---------
3 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index 276e3f49a4ae..f3dcd40f300c 100644
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@@ -187,6 +187,7 @@ void module_enable_nx(const struct module *mod);
void module_enable_x(const struct module *mod);
int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
char *secstrings, struct module *mod);
+bool module_check_misalignment(const struct module *mod);

#ifdef CONFIG_MODULE_SIG
int module_sig_check(struct load_info *info, int flags);
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 47addf849ef7..4876e2beb5b6 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2596,6 +2596,9 @@ 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);

+ if (module_check_misalignment(mod))
+ goto out_misaligned;
+
module_enable_ro(mod, false);
module_enable_nx(mod);
module_enable_x(mod);
@@ -2609,6 +2612,8 @@ static int complete_formation(struct module *mod, struct load_info *info)

return 0;

+out_misaligned:
+ err = -EINVAL;
out:
mutex_unlock(&module_mutex);
return err;
diff --git a/kernel/module/strict_rwx.c b/kernel/module/strict_rwx.c
index 6b99be9e88e1..14fbea66f12f 100644
--- a/kernel/module/strict_rwx.c
+++ b/kernel/module/strict_rwx.c
@@ -42,9 +42,6 @@ static void frob_text(const struct module_layout *layout,
static void frob_rodata(const struct module_layout *layout,
int (*set_memory)(unsigned long start, int num_pages))
{
- BUG_ON(!PAGE_ALIGNED(layout->base));
- BUG_ON(!PAGE_ALIGNED(layout->text_size));
- BUG_ON(!PAGE_ALIGNED(layout->ro_size));
set_memory((unsigned long)layout->base + layout->text_size,
(layout->ro_size - layout->text_size) >> PAGE_SHIFT);
}
@@ -52,9 +49,6 @@ static void frob_rodata(const struct module_layout *layout,
static void frob_ro_after_init(const struct module_layout *layout,
int (*set_memory)(unsigned long start, int num_pages))
{
- BUG_ON(!PAGE_ALIGNED(layout->base));
- BUG_ON(!PAGE_ALIGNED(layout->ro_size));
- BUG_ON(!PAGE_ALIGNED(layout->ro_after_init_size));
set_memory((unsigned long)layout->base + layout->ro_size,
(layout->ro_after_init_size - layout->ro_size) >> PAGE_SHIFT);
}
@@ -62,13 +56,29 @@ static void frob_ro_after_init(const struct module_layout *layout,
static void frob_writable_data(const struct module_layout *layout,
int (*set_memory)(unsigned long start, int num_pages))
{
- BUG_ON(!PAGE_ALIGNED(layout->base));
- BUG_ON(!PAGE_ALIGNED(layout->ro_after_init_size));
- BUG_ON(!PAGE_ALIGNED(layout->size));
set_memory((unsigned long)layout->base + layout->ro_after_init_size,
(layout->size - layout->ro_after_init_size) >> PAGE_SHIFT);
}

+static bool layout_check_misalignment(const struct module_layout *layout)
+{
+ return WARN_ON(!PAGE_ALIGNED(layout->base)) ||
+ WARN_ON(!PAGE_ALIGNED(layout->text_size)) ||
+ WARN_ON(!PAGE_ALIGNED(layout->ro_size)) ||
+ WARN_ON(!PAGE_ALIGNED(layout->ro_after_init_size)) ||
+ WARN_ON(!PAGE_ALIGNED(layout->size));
+}
+
+bool module_check_misalignment(const struct module *mod)
+{
+ if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
+ return false;
+
+ return layout_check_misalignment(&mod->core_layout) ||
+ layout_check_misalignment(&mod->data_layout) ||
+ layout_check_misalignment(&mod->init_layout);
+}
+
void module_enable_x(const struct module *mod)
{
if (!PAGE_ALIGNED(mod->core_layout.base) ||
--
2.34.1