[4/4] ptdump: add check_wx_pages debugfs attribute

Commit Message

Christophe Leroy Jan. 9, 2024, 12:14 p.m. UTC

Add a writable attribute in debugfs to trigger a
W^X pages check at any time.

To trigger the test, just echo any numeric value into
/sys/kernel/debug/check_wx_pages

The result is provided into dmesg.

Signed-off-by: Christophe Leroy <[e-mail]>
---
 mm/ptdump.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

Comments

Heiko Carstens Jan. 9, 2024, 1:50 p.m. UTC | #1

On Tue, Jan 09, 2024 at 01:14:38PM +0100, Christophe Leroy wrote:
> Add a writable attribute in debugfs to trigger a
> W^X pages check at any time.
> 
> To trigger the test, just echo any numeric value into
> /sys/kernel/debug/check_wx_pages
> 
> The result is provided into dmesg.
> 
> Signed-off-by: Christophe Leroy <[e-mail]>
> ---
>  mm/ptdump.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
...
> +static int check_wx_debugfs_set(void *data, u64 val)
> +{
> +	ptdump_check_wx();
> +
> +	return 0;
> +}
> +
> +DEFINE_SIMPLE_ATTRIBUTE(check_wx_fops, NULL, check_wx_debugfs_set, "%llu\n");
> +
> +static int ptdump_debugfs_init(void)
> +{
> +	debugfs_create_file("check_wx_pages", 0200, NULL, NULL, &check_wx_fops);
> +
> +	return 0;
> +}

Wouldn't it be better to have (only?) a readable attribute which triggers
this, and provides the result via this attribute?
That would allow for automated tests without having to parse dmesg.

Patch

diff --git a/mm/ptdump.c b/mm/ptdump.c
index 03c1bdae4a43..e154099c2584 100644
--- a/mm/ptdump.c
+++ b/mm/ptdump.c
@@ -1,6 +1,7 @@ 
 // SPDX-License-Identifier: GPL-2.0
 
 #include <linux/pagewalk.h>
+#include <linux/debugfs.h>
 #include <linux/ptdump.h>
 #include <linux/kasan.h>
 
@@ -163,3 +164,21 @@  void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)
 	/* Flush out the last page */
 	st->note_page(st, 0, -1, 0);
 }
+
+static int check_wx_debugfs_set(void *data, u64 val)
+{
+	ptdump_check_wx();
+
+	return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(check_wx_fops, NULL, check_wx_debugfs_set, "%llu\n");
+
+static int ptdump_debugfs_init(void)
+{
+	debugfs_create_file("check_wx_pages", 0200, NULL, NULL, &check_wx_fops);
+
+	return 0;
+}
+
+device_initcall(ptdump_debugfs_init);