From:   Andrew Donnellan <ajd@linux.ibm.com>
To:     linuxppc-dev@lists.ozlabs.org, linux-integrity@vger.kernel.org
Cc:     ruscur@russell.cc, bgray@linux.ibm.com, nayna@linux.ibm.com,
        gcwilson@linux.ibm.com, gjoyce@linux.ibm.com, brking@linux.ibm.com,
        stefanb@linux.ibm.com, sudhakar@linux.ibm.com,
        erichte@linux.ibm.com, gregkh@linuxfoundation.org,
        linux-kernel@vger.kernel.org, zohar@linux.ibm.com, joel@jms.id.au,
        npiggin@gmail.com
Subject: [PATCH v5 12/25] powerpc/secvar: Warn when PAGE_SIZE is smaller than max object size
Date:   Tue, 31 Jan 2023 17:39:15 +1100
Message-Id: <20230131063928.388035-13-ajd@linux.ibm.com>
In-Reply-To: <20230131063928.388035-1-ajd@linux.ibm.com>
References: <20230131063928.388035-1-ajd@linux.ibm.com>
MIME-Version: 1.0
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Precedence: bulk

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>

---

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);
-- 
2.39.1