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 <redacted>
Signed-off-by: Russell Currey <redacted>

---

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 2cbc60b37e4e..9b6be63b7b36 100644
--- a/arch/powerpc/kernel/secvar-sysfs.c
+++ b/arch/powerpc/kernel/secvar-sysfs.c

@@ -223,6 +223,7 @@ static int secvar_sysfs_load_static(void)
  
  static int secvar_sysfs_init(void)
  {
+	u64 max_size;
  	int rc;
  
  	if (!secvar_ops) {

@@ -272,6 +273,14 @@ 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);