* Re: [PATCH] loadpin: Implement custom proc_handler for enforce
2025-12-16 8:37 ` Kees Cook
@ 2025-12-17 13:25 ` Joel Granados
2025-12-19 10:55 ` Joel Granados
1 sibling, 0 replies; 4+ messages in thread
From: Joel Granados @ 2025-12-17 13:25 UTC (permalink / raw)
To: Kees Cook
Cc: Paul Moore, James Morris, Serge E. Hallyn, linux-security-module,
linux-kernel
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On Tue, Dec 16, 2025 at 12:37:29AM -0800, Kees Cook wrote:
> On Mon, Dec 15, 2025 at 04:43:48PM +0100, Joel Granados wrote:
> > The new proc_handler_loadpin returns -EINVAL when is_loadpin_writable is
> > false and the kernel var (enforce) is being written. Move
> > loadpin_sysctl_table to .rodata (by const qualifying it) as there is no
> > need to change the value of the extra1 entry.
> >
> > Signed-off-by: Joel Granados <joel.granados@kernel.org>
> > ---
> > Const qualifying ctl tables is part of the hardening effort in the linux
> > kernel.
>
> Ah yes, thanks for getting through these "weird" cases! :)
>
> > ---
> > security/loadpin/loadpin.c | 21 ++++++++++++++++-----
> > 1 file changed, 16 insertions(+), 5 deletions(-)
> >
> > diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
> > index 273ffbd6defe1324d6688dec5f9fe6c9401283ed..f049c81b82a78265b6ae358bb2a814265cec9f16 100644
> > --- a/security/loadpin/loadpin.c
> > +++ b/security/loadpin/loadpin.c
> > @@ -53,18 +53,29 @@ static bool deny_reading_verity_digests;
> > #endif
> >
> > #ifdef CONFIG_SYSCTL
> > -static struct ctl_table loadpin_sysctl_table[] = {
> > +static bool is_loadpin_writable;
>
> I would rather that load_root_writable were declared external to
> loadpin_check(), and then we could remove set_sysctl() entirely, instead
> using load_root_writable as the thing to check in proc_handler_loadpin().
This seems like a better approach :).
>
> And also rename load_root_writable to "loadpin_root_writable", just to
> make it a bit more clear.
And the default value of loadpin_root_writable would be false. right?
Something like this:
diff --git c/security/loadpin/loadpin.c w/security/loadpin/loadpin.c
index 273ffbd6defe..650073829db4 100644
--- c/security/loadpin/loadpin.c
+++ w/security/loadpin/loadpin.c
@@ -53,44 +53,40 @@ static bool deny_reading_verity_digests;
#endif
#ifdef CONFIG_SYSCTL
-static struct ctl_table loadpin_sysctl_table[] = {
+static bool loadpin_root_writable;
+
+static int proc_handler_loadpin(const struct ctl_table *table, int dir,
+ void *buffer, size_t *lenp, loff_t *ppos)
+{
+ if (!loadpin_root_writable && SYSCTL_USER_TO_KERN(dir))
+ return -EINVAL;
+ return proc_dointvec_minmax(table, dir, buffer, lenp, ppos);
+}
+
+static const struct ctl_table loadpin_sysctl_table[] = {
{
.procname = "enforce",
.data = &enforce,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec_minmax,
- .extra1 = SYSCTL_ONE,
+ .proc_handler = proc_handler_loadpin,
+ .extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE,
},
};
-
-static void set_sysctl(bool is_writable)
-{
- /*
- * If load pinning is not enforced via a read-only block
- * device, allow sysctl to change modes for testing.
- */
- if (is_writable)
- loadpin_sysctl_table[0].extra1 = SYSCTL_ZERO;
- else
- loadpin_sysctl_table[0].extra1 = SYSCTL_ONE;
-}
-#else
-static inline void set_sysctl(bool is_writable) { }
#endif
-static void report_writable(struct super_block *mnt_sb, bool writable)
+static void report_writable(struct super_block *mnt_sb)
{
if (mnt_sb->s_bdev) {
pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev,
MAJOR(mnt_sb->s_bdev->bd_dev),
MINOR(mnt_sb->s_bdev->bd_dev),
- writable ? "writable" : "read-only");
+ loadpin_root_writable ? "writable" : "read-only");
} else
pr_info("mnt_sb lacks block device, treating as: writable\n");
- if (!writable)
+ if (!loadpin_root_writable)
pr_info("load pinning engaged.\n");
}
@@ -168,8 +164,8 @@ static int loadpin_check(struct file *file, enum kernel_read_file_id id)
spin_unlock(&pinned_root_spinlock);
if (first_root_pin) {
- report_writable(pinned_root, load_root_writable);
- set_sysctl(load_root_writable);
+ loadpin_root_writable = sb_is_writable(pinned_root);
+ report_writable(pinned_root);
report_load(origin, file, "pinned");
}
--
Joel Granados
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^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] loadpin: Implement custom proc_handler for enforce
2025-12-16 8:37 ` Kees Cook
2025-12-17 13:25 ` Joel Granados
@ 2025-12-19 10:55 ` Joel Granados
1 sibling, 0 replies; 4+ messages in thread
From: Joel Granados @ 2025-12-19 10:55 UTC (permalink / raw)
To: Kees Cook
Cc: Paul Moore, James Morris, Serge E. Hallyn, linux-security-module,
linux-kernel
[-- Attachment #1: Type: text/plain, Size: 1632 bytes --]
Sent out a V2
On Tue, Dec 16, 2025 at 12:37:29AM -0800, Kees Cook wrote:
> On Mon, Dec 15, 2025 at 04:43:48PM +0100, Joel Granados wrote:
> > The new proc_handler_loadpin returns -EINVAL when is_loadpin_writable is
> > false and the kernel var (enforce) is being written. Move
> > loadpin_sysctl_table to .rodata (by const qualifying it) as there is no
> > need to change the value of the extra1 entry.
> >
> > Signed-off-by: Joel Granados <joel.granados@kernel.org>
> > ---
> > Const qualifying ctl tables is part of the hardening effort in the linux
> > kernel.
>
> Ah yes, thanks for getting through these "weird" cases! :)
>
> > ---
> > security/loadpin/loadpin.c | 21 ++++++++++++++++-----
> > 1 file changed, 16 insertions(+), 5 deletions(-)
> >
> > diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
> > index 273ffbd6defe1324d6688dec5f9fe6c9401283ed..f049c81b82a78265b6ae358bb2a814265cec9f16 100644
> > --- a/security/loadpin/loadpin.c
> > +++ b/security/loadpin/loadpin.c
> > @@ -53,18 +53,29 @@ static bool deny_reading_verity_digests;
> > #endif
> >
> > #ifdef CONFIG_SYSCTL
> > -static struct ctl_table loadpin_sysctl_table[] = {
> > +static bool is_loadpin_writable;
>
> I would rather that load_root_writable were declared external to
> loadpin_check(), and then we could remove set_sysctl() entirely, instead
> using load_root_writable as the thing to check in proc_handler_loadpin().
>
> And also rename load_root_writable to "loadpin_root_writable", just to
> make it a bit more clear.
>
> -Kees
>
> --
> Kees Cook
--
Joel Granados
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^ permalink raw reply [flat|nested] 4+ messages in thread