parisc: Allow mmap(MAP_STACK) memory to automatically expand upwards

commit 5d69896 upstream.

When userspace allocates memory with mmap() in order to be used for stack,
allow this memory region to automatically expand upwards up until the
current maximum process stack size.
The fault handler checks if the VM_GROWSUP bit is set in the vm_flags field
of a memory area before it allows it to expand.
This patch modifies the parisc specific code only.
A RFC for a generic patch to modify mmap() for all architectures was sent
to the mailing list but did not get enough Acks.

Reported-by: Camm Maguire <camm@maguirefamily.org>
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org	# v5.10+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: hdeller

arch/parisc/include/asm/mman.h

@@ -11,4 +11,18 @@ static inline bool arch_memory_deny_write_exec_supported(void)
 }
 #define arch_memory_deny_write_exec_supported arch_memory_deny_write_exec_supported
 
+static inline unsigned long arch_calc_vm_flag_bits(unsigned long flags)
+{
+	/*
+	 * The stack on parisc grows upwards, so if userspace requests memory
+	 * for a stack, mark it with VM_GROWSUP so that the stack expansion in
+	 * the fault handler will work.
+	 */
+	if (flags & MAP_STACK)
+		return VM_GROWSUP;
+
+	return 0;
+}
+#define arch_calc_vm_flag_bits(flags) arch_calc_vm_flag_bits(flags)
+
 #endif /* __ASM_MMAN_H__ */