[PATCH v6 12/26] powerpc/secvar: Warn when PAGE_SIZE is smaller than max object size

Andrew Donnellan
2023-02-10T08:04:59Z

Due to sysfs constraints, when writing to a variable, we can only handle
writes of up to PAGE_SIZE.

It's possible that the maximum object size is larger than PAGE_SIZE, in
which case, print a warning on boot so that the user is aware.

Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Russell Currey <ruscur@russell.cc>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>

---

v3: New patch (ajd)
---
arch/powerpc/kernel/secvar-sysfs.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/arch/powerpc/kernel/secvar-sysfs.c b/arch/powerpc/kernel/secvar-sysfs.c
index bfb19f22c6ba..6ba23b2bb9da 100644
--- a/arch/powerpc/kernel/secvar-sysfs.c
+++ b/arch/powerpc/kernel/secvar-sysfs.c
@@ -225,6 +225,7 @@ static int secvar_sysfs_load_static(void)

static int secvar_sysfs_init(void)
{
+ u64 max_size;
int rc;

if (!secvar_ops) {
@@ -274,6 +275,14 @@ static int secvar_sysfs_init(void)
goto err;
}

+ // Due to sysfs limitations, we will only ever get a write buffer of
+ // up to 1 page in size. Print a warning if this is potentially going
+ // to cause problems, so that the user is aware.
+ secvar_ops->max_size(&max_size);
+ if (max_size > PAGE_SIZE)
+ pr_warn_ratelimited("PAGE_SIZE (%lu) is smaller than maximum object size (%llu), writes are limited to PAGE_SIZE\n",
+ PAGE_SIZE, max_size);
+
return 0;
err:
kobject_put(secvar_kobj);
--
2.39.1