x86/pkey: Fix undefined behaviour with PKRU_WD_BIT

Both __pkru_allows_write() and arch_set_user_pkey_access() shift
PKRU_WD_BIT (a signed constant) by up to 30 bits, hitting the
sign bit.

Use unsigned constants instead.

Clearly pkey 15 has not been used in combination with UBSAN yet.

Noticed by code inspection only.  I can't actually provoke the
compiler into generating incorrect logic as far as this shift is
concerned.

[
  dhansen: add stable@ tag, plus minor changelog massaging,

           For anyone doing backports, these #defines were in
	   arch/x86/include/asm/pgtable.h before 784a46618f.
]

Fixes: 33a709b25a ("mm/gup, x86/mm/pkeys: Check VMAs and PTEs for protection keys")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20211216000856.4480-1-andrew.cooper3@citrix.com

arch/x86/include/asm/pkru.h

@@ -4,8 +4,8 @@
 
 #include <asm/cpufeature.h>
 
-#define PKRU_AD_BIT 0x1
-#define PKRU_WD_BIT 0x2
+#define PKRU_AD_BIT 0x1u
+#define PKRU_WD_BIT 0x2u
 #define PKRU_BITS_PER_PKEY 2
 
 #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS