[PATCH] modules: always page-align module section allocations

From: Jessica Yu
Date: Wed Jul 24 2019 - 11:02:26 EST

Some arches (e.g., arm64, x86) have moved towards non-executable
module_alloc() allocations for security hardening reasons. That means
that the module loader will need to set the text section of a module to
executable, regardless of whether or not CONFIG_STRICT_MODULE_RWX is set.

When CONFIG_STRICT_MODULE_RWX=y, module section allocations are always
page-aligned to handle memory rwx permissions. On some arches with
CONFIG_STRICT_MODULE_RWX=n however, when setting the module text to
executable, the BUG_ON() in frob_text() gets triggered since module
section allocations are not page-aligned when CONFIG_STRICT_MODULE_RWX=n.
Since the set_memory_* API works with pages, and since we need to call
set_memory_x() regardless of whether CONFIG_STRICT_MODULE_RWX is set, we
might as well page-align all module section allocations for ease of
managing rwx permissions of module sections (text, rodata, etc).

Fixes: 2eef1399a866 ("modules: fix BUG when load module with rodata=n")
Reported-by: Martin Kaiser <lists@xxxxxxxxx>
Reported-by: Bartosz Golaszewski <brgl@xxxxxxxx>
Tested-by: David Lechner <david@xxxxxxxxxxxxxx>
Tested-by: Martin Kaiser <martin@xxxxxxxxx>
Signed-off-by: Jessica Yu <jeyu@xxxxxxxxxx>
kernel/module.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 5933395af9a0..cd8df516666d 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -64,14 +64,9 @@

* Modules' sections will be aligned on page boundaries
- * to ensure complete separation of code and data, but
+ * to ensure complete separation of code and data
# define debug_align(X) ALIGN(X, PAGE_SIZE)
-# define debug_align(X) (X)

/* If this is set, the section belongs in the init part of the module */