linux-kernel - [PATCH v2 3/4] module: Rework layout alignment to avoid BUG

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Message-Id: <f13c61751da92ca56ea06d5687e567c3468c6ab3.1645542447.git.christophe.leroy@csgroup.eu>
Date:   Tue, 22 Feb 2022 16:12:18 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Luis Chamberlain <mcgrof@...nel.org>, linux-modules@...r.kernel.org
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/4] module: Rework layout alignment to avoid BUG_ON()s

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@...roup.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