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powerpc/pseries/papr-sysparm: Validate buffer object lengths

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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@linux.ibm.com
This commit is contained in:
Nathan Lynch 2023-12-12 11:01:57 -06:00 committed by Michael Ellerman
parent 514f6ff436
commit 35aae182bd
1 changed files with 47 additions and 0 deletions
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47
arch/powerpc/platforms/pseries/papr-sysparm.c
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@ -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));