6.6-stable review patch. If anyone has any objections, please let me know.
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From: Nathan Lynch nathanl@linux.ibm.com
[ Upstream commit 35aae182bd7b422be3cefc08c12207bf2b973364 ]
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 Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://msgid.link/20231212-papr-sys_rtas-vs-lockdown-v6-10-e9eafd0c8c6c@lin... Signed-off-by: Sasha Levin sashal@kernel.org --- 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 fedc61599e6cc..a1e7aeac74161 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));