From: Nathan Lynch via B4 Relay <devnull+nathanl.linux.ibm.com@kernel.org>
To: Michael Ellerman <mpe@ellerman.id.au>,
Nicholas Piggin <npiggin@gmail.com>
Cc: "Nathan Lynch" <nathanl@linux.ibm.com>,
tyreld@linux.ibm.com, gcwilson@linux.ibm.com,
"Aneesh Kumar K.V (IBM)" <aneesh.kumar@kernel.org>,
"Michal Suchánek" <msuchanek@suse.de>,
linuxppc-dev@lists.ozlabs.org
Subject: [PATCH v6 10/13] powerpc/pseries/papr-sysparm: Validate buffer object lengths
Date: Tue, 12 Dec 2023 11:01:57 -0600 [thread overview]
Message-ID: <20231212-papr-sys_rtas-vs-lockdown-v6-10-e9eafd0c8c6c@linux.ibm.com> (raw)
In-Reply-To: <20231212-papr-sys_rtas-vs-lockdown-v6-0-e9eafd0c8c6c@linux.ibm.com>
From: Nathan Lynch <nathanl@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 <nathanl@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
next prev parent reply other threads:[~2023-12-12 17:10 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-12 17:01 [PATCH v6 00/13] powerpc/pseries: New character devices for system parameters and VPD Nathan Lynch via B4 Relay
2023-12-12 17:01 ` [PATCH v6 01/13] powerpc/rtas: Avoid warning on invalid token argument to sys_rtas() Nathan Lynch via B4 Relay
2023-12-12 17:01 ` [PATCH v6 02/13] powerpc/rtas: Add for_each_rtas_function() iterator Nathan Lynch via B4 Relay
2023-12-12 17:01 ` [PATCH v6 03/13] powerpc/rtas: Fall back to linear search on failed token->function lookup Nathan Lynch via B4 Relay
2023-12-12 17:01 ` [PATCH v6 04/13] powerpc/rtas: Add function return status constants Nathan Lynch via B4 Relay
2023-12-12 17:01 ` [PATCH v6 05/13] powerpc/rtas: Move token validation from block_rtas_call() to sys_rtas() Nathan Lynch via B4 Relay
2023-12-12 17:01 ` [PATCH v6 06/13] powerpc/rtas: Facilitate high-level call sequences Nathan Lynch via B4 Relay
2023-12-12 17:01 ` [PATCH v6 07/13] powerpc/rtas: Serialize firmware activation sequences Nathan Lynch via B4 Relay
2023-12-12 17:01 ` [PATCH v6 08/13] powerpc/rtas: Warn if per-function lock isn't held Nathan Lynch via B4 Relay
2023-12-12 17:01 ` [PATCH v6 09/13] powerpc/pseries: Add papr-vpd character driver for VPD retrieval Nathan Lynch via B4 Relay
2023-12-12 17:01 ` Nathan Lynch via B4 Relay [this message]
2023-12-12 17:01 ` [PATCH v6 11/13] powerpc/pseries/papr-sysparm: Expose character device to user space Nathan Lynch via B4 Relay
2023-12-12 17:01 ` [PATCH v6 12/13] powerpc/selftests: Add test for papr-vpd Nathan Lynch via B4 Relay
2023-12-12 17:02 ` [PATCH v6 13/13] powerpc/selftests: Add test for papr-sysparm Nathan Lynch via B4 Relay
2023-12-21 10:38 ` [PATCH v6 00/13] powerpc/pseries: New character devices for system parameters and VPD Michael Ellerman
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