[PATCH RESEND 2/2] ARM: prctl: Reject PR_SET_MDWE on pre-ARMv6

[Zev Weiss <zev@bewilderbeest.net>]

On v5 and lower CPUs we can't provide MDWE protection, so ensure we
fail any attempt to enable it via prctl(PR_SET_MDWE).

Previously such an attempt would misleadingly succeed, leading to any
subsequent mmap(PROT_READ|PROT_WRITE) or execve() failing
unconditionally (the latter somewhat violently via
force_fatal_sig(SIGSEGV) due to READ_IMPLIES_EXEC).

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Cc: <stable@vger.kernel.org> # v6.3+
---
 arch/arm/include/asm/mman.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
 create mode 100644 arch/arm/include/asm/mman.h

diff --git a/arch/arm/include/asm/mman.h b/arch/arm/include/asm/mman.h
new file mode 100644
index 000000000000..2189e507c8e0
--- /dev/null
+++ b/arch/arm/include/asm/mman.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_MMAN_H__
+#define __ASM_MMAN_H__
+
+#include <asm/system_info.h>
+#include <uapi/asm/mman.h>
+
+static inline bool arch_memory_deny_write_exec_supported(void)
+{
+	return cpu_architecture() >= CPU_ARCH_ARMv6;
+}
+#define arch_memory_deny_write_exec_supported arch_memory_deny_write_exec_supported
+
+#endif /* __ASM_MMAN_H__ */
-- 
2.43.2