From: Nathan Lynch <nath...@linux.ibm.com>
The ability to get and set system parameters will be exposed to user
space, so let's get a little more strict about malformed
papr_sysparm_buf objects.
* Create accessors for the length field of struct papr_sysparm_buf.
The length is always stored in MSB order and this is better than
spreading the necessary conversions all over.
* Reject attempts to submit invalid buffers to RTAS.
* Warn if RTAS returns a buffer with an invalid length, clamping the
returned length to a safe value that won't overrun the buffer.
These are meant as precautionary measures to mitigate both firmware
and kernel bugs in this area, should they arise, but I am not aware of
any.
Signed-off-by: Nathan Lynch <nath...@linux.ibm.com>
---
arch/powerpc/platforms/pseries/papr-sysparm.c | 47 +++++++++++++++++++++++++++
1 file changed, 47 insertions(+)
diff --git a/arch/powerpc/platforms/pseries/papr-sysparm.c
b/arch/powerpc/platforms/pseries/papr-sysparm.c
index fedc61599e6c..a1e7aeac7416 100644
--- a/arch/powerpc/platforms/pseries/papr-sysparm.c
+++ b/arch/powerpc/platforms/pseries/papr-sysparm.c
@@ -23,6 +23,46 @@ void papr_sysparm_buf_free(struct papr_sysparm_buf *buf)
kfree(buf);
}
+static size_t papr_sysparm_buf_get_length(const struct papr_sysparm_buf *buf)
+{
+ return be16_to_cpu(buf->len);
+}
+
+static void papr_sysparm_buf_set_length(struct papr_sysparm_buf *buf, size_t
length)
+{
+ WARN_ONCE(length > sizeof(buf->val),
+ "bogus length %zu, clamping to safe value", length);
+ length = min(sizeof(buf->val), length);
+ buf->len = cpu_to_be16(length);
+}
+
+/*
+ * For use on buffers returned from ibm,get-system-parameter before
+ * returning them to callers. Ensures the encoded length of valid data
+ * cannot overrun buf->val[].
+ */
+static void papr_sysparm_buf_clamp_length(struct papr_sysparm_buf *buf)
+{
+ papr_sysparm_buf_set_length(buf, papr_sysparm_buf_get_length(buf));
+}
+
+/*
+ * Perform some basic diligence on the system parameter buffer before
+ * submitting it to RTAS.
+ */
+static bool papr_sysparm_buf_can_submit(const struct papr_sysparm_buf *buf)
+{
+ /*
+ * Firmware ought to reject buffer lengths that exceed the
+ * maximum specified in PAPR, but there's no reason for the
+ * kernel to allow them either.
+ */
+ if (papr_sysparm_buf_get_length(buf) > sizeof(buf->val))
+ return false;
+
+ return true;
+}
+
/**
* papr_sysparm_get() - Retrieve the value of a PAPR system parameter.
* @param: PAPR system parameter token as described in
@@ -63,6 +103,9 @@ int papr_sysparm_get(papr_sysparm_t param, struct
papr_sysparm_buf *buf)
if (token == RTAS_UNKNOWN_SERVICE)
return -ENOENT;
+ if (!papr_sysparm_buf_can_submit(buf))
+ return -EINVAL;
+
work_area = rtas_work_area_alloc(sizeof(*buf));
memcpy(rtas_work_area_raw_buf(work_area), buf, sizeof(*buf));
@@ -77,6 +120,7 @@ int papr_sysparm_get(papr_sysparm_t param, struct
papr_sysparm_buf *buf)
case 0:
ret = 0;
memcpy(buf, rtas_work_area_raw_buf(work_area), sizeof(*buf));
+ papr_sysparm_buf_clamp_length(buf);
break;
case -3: /* parameter not implemented */
ret = -EOPNOTSUPP;
@@ -115,6 +159,9 @@ int papr_sysparm_set(papr_sysparm_t param, const struct
papr_sysparm_buf *buf)
if (token == RTAS_UNKNOWN_SERVICE)
return -ENOENT;
+ if (!papr_sysparm_buf_can_submit(buf))
+ return -EINVAL;
+
work_area = rtas_work_area_alloc(sizeof(*buf));
memcpy(rtas_work_area_raw_buf(work_area), buf, sizeof(*buf));
--
2.41.0
