[PATCH v2] arm64: add check_wx_pages debugfs for CHECK_WX

[Phong Tran]

follow the suggestion from
https://github.com/KSPP/linux/issues/35

Signed-off-by: Phong Tran <tranmanphong@xxxxxxxxx>
---
Change since v1:
- Update the Kconfig help text
- Don't check the return value of debugfs_create_file()
- Tested on QEMU aarch64
root@qemuarm64:~# zcat /proc/config.gz | grep PTDUMP
CONFIG_GENERIC_PTDUMP=y
CONFIG_PTDUMP_CORE=y
CONFIG_PTDUMP_DEBUGFS=y
root@qemuarm64:~# uname -a
Linux qemuarm64 5.7.0-rc2-00001-g20ddb383c313 #3 SMP PREEMPT Tue Apr 21 23:18:56 +07 2020 aarch64 GNU/Linux
root@qemuarm64:~# echo 1 > /sys/kernel/debug/check_wx_pages
[   63.261868] Checked W+X mappings: passed, no W+X pages found
---
 arch/arm64/Kconfig.debug        |  5 ++++-
 arch/arm64/include/asm/ptdump.h |  2 ++
 arch/arm64/mm/dump.c            |  1 +
 arch/arm64/mm/ptdump_debugfs.c  | 18 ++++++++++++++++++
 4 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
index a1efa246c9ed..cd82c9d3664a 100644
--- a/arch/arm64/Kconfig.debug
+++ b/arch/arm64/Kconfig.debug
@@ -48,7 +48,10 @@ config DEBUG_WX
 	  of other unfixed kernel bugs easier.
 
 	  There is no runtime or memory usage effect of this option
-	  once the kernel has booted up - it's a one time check.
+	  once the kernel has booted up - it's a one time check at
+	  boot, and can also be triggered at runtime by echo "1" to
+	  "check_wx_pages". The "check_wx_pages" is available only with
+	  CONFIG_PTDUMP_DEBUGFS is enabled.
 
 	  If in doubt, say "Y".
 
diff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h
index 38187f74e089..c90a6ec6f59b 100644
--- a/arch/arm64/include/asm/ptdump.h
+++ b/arch/arm64/include/asm/ptdump.h
@@ -24,9 +24,11 @@ struct ptdump_info {
 void ptdump_walk(struct seq_file *s, struct ptdump_info *info);
 #ifdef CONFIG_PTDUMP_DEBUGFS
 void ptdump_debugfs_register(struct ptdump_info *info, const char *name);
+void ptdump_check_wx_init(void);
 #else
 static inline void ptdump_debugfs_register(struct ptdump_info *info,
 					   const char *name) { }
+static inline void ptdump_check_wx_init(void) { }
 #endif
 void ptdump_check_wx(void);
 #endif /* CONFIG_PTDUMP_CORE */
diff --git a/arch/arm64/mm/dump.c b/arch/arm64/mm/dump.c
index 860c00ec8bd3..60c99a047763 100644
--- a/arch/arm64/mm/dump.c
+++ b/arch/arm64/mm/dump.c
@@ -378,6 +378,7 @@ static int ptdump_init(void)
 #endif
 	ptdump_initialize();
 	ptdump_debugfs_register(&kernel_ptdump_info, "kernel_page_tables");
+	ptdump_check_wx_init();
 	return 0;
 }
 device_initcall(ptdump_init);
diff --git a/arch/arm64/mm/ptdump_debugfs.c b/arch/arm64/mm/ptdump_debugfs.c
index d29d722ec3ec..6b0aa16cb17b 100644
--- a/arch/arm64/mm/ptdump_debugfs.c
+++ b/arch/arm64/mm/ptdump_debugfs.c
@@ -20,3 +20,21 @@ void ptdump_debugfs_register(struct ptdump_info *info, const char *name)
 {
 	debugfs_create_file(name, 0400, NULL, info, &ptdump_fops);
 }
+
+static int check_wx_debugfs_set(void *data, u64 val)
+{
+	if (val != 1ULL)
+		return -EINVAL;
+
+	ptdump_check_wx();
+
+	return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(check_wx_fops, NULL, check_wx_debugfs_set, "%llu\n");
+
+void ptdump_check_wx_init(void)
+{
+	debugfs_create_file("check_wx_pages", 0200, NULL,
+			NULL, &check_wx_fops) ? 0 : -ENOMEM;
+}
-- 
2.20.1