um: virt-pci: Avoid GCC non-NULL warning

GCC gets confused about the return value of get_cpu_var() possibly
being NULL, so explicitly test for it before calls to memcpy() and
memset(). Avoids warnings like this:

   arch/um/drivers/virt-pci.c: In function 'um_pci_send_cmd':
   include/linux/fortify-string.h:48:33: warning: argument 1 null where non-null expected [-Wnonnull]
      48 | #define __underlying_memcpy     __builtin_memcpy
         |                                 ^
   include/linux/fortify-string.h:438:9: note: in expansion of macro '__underlying_memcpy'
     438 |         __underlying_##op(p, q, __fortify_size);                        \
         |         ^~~~~~~~~~~~~
   include/linux/fortify-string.h:483:26: note: in expansion of macro '__fortify_memcpy_chk'
     483 | #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,                  \
         |                          ^~~~~~~~~~~~~~~~~~~~
   arch/um/drivers/virt-pci.c:100:9: note: in expansion of macro 'memcpy'
     100 |         memcpy(buf, cmd, cmd_size);
         |         ^~~~~~

While at it, avoid literal "8" and use stored sizeof(buf->data) in
memset() and um_pci_send_cmd().

Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/202211271212.SUZSC9f9-lkp@intel.com
Fixes: ba38961a069b ("um: Enable FORTIFY_SOURCE")
Cc: Richard Weinberger <richard@nod.at>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Xiu Jianfeng <xiujianfeng@huawei.com>
Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>
Cc: linux-um@lists.infradead.org
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/arch/um/drivers/virt-pci.c b/arch/um/drivers/virt-pci.c
index acb55b3..3ac220d 100644 (file)
--- a/arch/um/drivers/virt-pci.c
+++ b/arch/um/drivers/virt-pci.c
@@ -97,7 +97,8 @@ static int um_pci_send_cmd(struct um_pci_device *dev,
        }
 
        buf = get_cpu_var(um_pci_msg_bufs);
-       memcpy(buf, cmd, cmd_size);
+       if (buf)
+               memcpy(buf, cmd, cmd_size);
 
        if (posted) {
                u8 *ncmd = kmalloc(cmd_size + extra_size, GFP_ATOMIC);
@@ -182,6 +183,7 @@ static unsigned long um_pci_cfgspace_read(void *priv, unsigned int offset,
        struct um_pci_message_buffer *buf;
        u8 *data;
        unsigned long ret = ULONG_MAX;
+       size_t bytes = sizeof(buf->data);
 
        if (!dev)
                return ULONG_MAX;
@@ -189,7 +191,8 @@ static unsigned long um_pci_cfgspace_read(void *priv, unsigned int offset,
        buf = get_cpu_var(um_pci_msg_bufs);
        data = buf->data;
 
-       memset(buf->data, 0xff, sizeof(buf->data));
+       if (buf)
+               memset(data, 0xff, bytes);
 
        switch (size) {
        case 1:
@@ -204,7 +207,7 @@ static unsigned long um_pci_cfgspace_read(void *priv, unsigned int offset,
                goto out;
        }
 
-       if (um_pci_send_cmd(dev, &hdr, sizeof(hdr), NULL, 0, data, 8))
+       if (um_pci_send_cmd(dev, &hdr, sizeof(hdr), NULL, 0, data, bytes))
                goto out;
 
        switch (size) {