[PATCH v3] powerpc: Fix virt_addr_valid() check

[Kefeng Wang <wangkefeng.wang@huawei.com>]

When run ethtool eth0 on PowerPC64, the BUG occurred,

  usercopy: Kernel memory exposure attempt detected from SLUB object not in SLUB page?! (offset 0, size 1048)!
  kernel BUG at mm/usercopy.c:99
  ...
  usercopy_abort+0x64/0xa0 (unreliable)
  __check_heap_object+0x168/0x190
  __check_object_size+0x1a0/0x200
  dev_ethtool+0x2494/0x2b20
  dev_ioctl+0x5d0/0x770
  sock_do_ioctl+0xf0/0x1d0
  sock_ioctl+0x3ec/0x5a0
  __se_sys_ioctl+0xf0/0x160
  system_call_exception+0xfc/0x1f0
  system_call_common+0xf8/0x200

The code shows below,

  data = vzalloc(array_size(gstrings.len, ETH_GSTRING_LEN));
  copy_to_user(useraddr, data, gstrings.len * ETH_GSTRING_LEN))

The data is alloced by vmalloc(), virt_addr_valid(ptr) will return true
on PowerPC64, which leads to the panic.

As commit 4dd7554a6456 ("powerpc/64: Add VIRTUAL_BUG_ON checks for __va
and __pa addresses") does, let's check the virt addr above PAGE_OFFSET in
the virt_addr_valid() for PowerPC64, which will make sure that the passed
address is a valid linear map address.

Meanwhile, PAGE_OFFSET is the virtual address of the start of lowmem,
the check is suitable for PowerPC32 too.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
v3:
- update changelog and remove a redundant cast 
 arch/powerpc/include/asm/page.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
index 254687258f42..a8a29a23ce2d 100644
--- a/arch/powerpc/include/asm/page.h
+++ b/arch/powerpc/include/asm/page.h
@@ -132,7 +132,10 @@ static inline bool pfn_valid(unsigned long pfn)
 #define virt_to_page(kaddr)	pfn_to_page(virt_to_pfn(kaddr))
 #define pfn_to_kaddr(pfn)	__va((pfn) << PAGE_SHIFT)
 
-#define virt_addr_valid(kaddr)	pfn_valid(virt_to_pfn(kaddr))
+#define virt_addr_valid(vaddr)	({						\
+	unsigned long _addr = (unsigned long)vaddr;				\
+	_addr >= PAGE_OFFSET && pfn_valid(virt_to_pfn(_addr));	\
+})
 
 /*
  * On Book-E parts we need __va to parse the device tree and we can't
-- 
2.26.2