arm64: Ignore the 'write' ESR flag on cache maintenance faults

ESR.WnR bit is always set on data cache maintenance faults even though
the page is not required to have write permission. If a translation
fault (page not yet mapped) happens for read-only user address range,
Linux incorrectly assumes a permission fault. This patch adds the check
of the ESR.CM bit during the page fault handling to ignore the 'write'
flag.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Tim Northover <Tim.Northover@arm.com>
Cc: stable@vger.kernel.org

arch/arm64/mm/fault.c

@@ -148,6 +148,7 @@ void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *regs)
 #define VM_FAULT_BADACCESS	0x020000
 
 #define ESR_WRITE		(1 << 6)
+#define ESR_CM			(1 << 8)
 #define ESR_LNX_EXEC		(1 << 24)
 
 /*
@@ -206,7 +207,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 	struct task_struct *tsk;
 	struct mm_struct *mm;
 	int fault, sig, code;
-	int write = esr & ESR_WRITE;
+	bool write = (esr & ESR_WRITE) && !(esr & ESR_CM);
 	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
 		(write ? FAULT_FLAG_WRITE : 0);