From 527701eda5f196588df9b36a30651804fea7d1a7 Mon Sep 17 00:00:00 2001
From: Palmer Dabbelt <palmerdabbelt@google.com>
Date: Thu, 9 Jul 2020 11:43:21 -0700
Subject: [PATCH] lib: Add a generic version of devmem_is_allowed()
As part of adding support for STRICT_DEVMEM to the RISC-V port, Zong
provided a devmem_is_allowed() implementation that's exactly the same as
all the others I checked. Instead I'm adding a generic version, which
will soon be used.
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
---
include/asm-generic/io.h | 4 ++++
lib/Kconfig | 3 +++
lib/Kconfig.debug | 2 +-
lib/Makefile | 2 ++
lib/devmem_is_allowed.c | 27 +++++++++++++++++++++++++++
5 files changed, 37 insertions(+), 1 deletion(-)
create mode 100644 lib/devmem_is_allowed.c
diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index dabf8cb7203b..da2e861dee1c 100644
--- a/include/asm-generic/io.h
+++ b/include/asm-generic/io.h
@@ -1122,6 +1122,10 @@ static inline void memcpy_toio(volatile void __iomem *addr, const void *buffer,
}
#endif
+#ifndef CONFIG_GENERIC_DEVMEM_IS_ALLOWED
+extern int devmem_is_allowed(unsigned long pfn);
+#endif
+
#endif /* __KERNEL__ */
#endif /* __ASM_GENERIC_IO_H */
diff --git a/lib/Kconfig b/lib/Kconfig
index b4b98a03ff98..b26721cf51bc 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -681,6 +681,9 @@ config GENERIC_LIB_CMPDI2
config GENERIC_LIB_UCMPDI2
bool
+config GENERIC_LIB_DEVMEM_IS_ALLOWED
+ bool
+
config PLDMFW
bool
default n
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 0c781f912f9f..87410f62b501 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1626,7 +1626,7 @@ config ARCH_HAS_DEVMEM_IS_ALLOWED
config STRICT_DEVMEM
bool "Filter access to /dev/mem"
depends on MMU && DEVMEM
- depends on ARCH_HAS_DEVMEM_IS_ALLOWED
+ depends on ARCH_HAS_DEVMEM_IS_ALLOWED || GENERIC_LIB_DEVMEM_IS_ALLOWED
default y if PPC || X86 || ARM64
help
If this option is disabled, you allow userspace (root) access to all
diff --git a/lib/Makefile b/lib/Makefile
index a4a4c6864f51..34011a11fbb3 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -348,3 +348,5 @@ obj-$(CONFIG_PLDMFW) += pldmfw/
obj-$(CONFIG_LIST_KUNIT_TEST) += list-test.o
obj-$(CONFIG_LINEAR_RANGES_TEST) += test_linear_ranges.o
obj-$(CONFIG_BITS_TEST) += test_bits.o
+
+obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
diff --git a/lib/devmem_is_allowed.c b/lib/devmem_is_allowed.c
new file mode 100644
index 000000000000..c0d67c541849
--- /dev/null
+++ b/lib/devmem_is_allowed.c
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * A generic version of devmem_is_allowed.
+ *
+ * Based on arch/arm64/mm/mmap.c
+ *
+ * Copyright (C) 2020 Google, Inc.
+ * Copyright (C) 2012 ARM Ltd.
+ */
+
+#include <linux/mm.h>
+#include <linux/ioport.h>
+
+/*
+ * devmem_is_allowed() checks to see if /dev/mem access to a certain address
+ * is valid. The argument is a physical page number. We mimic x86 here by
+ * disallowing access to system RAM as well as device-exclusive MMIO regions.
+ * This effectively disable read()/write() on /dev/mem.
+ */
+int devmem_is_allowed(unsigned long pfn)
+{
+ if (iomem_is_exclusive(pfn << PAGE_SHIFT))
+ return 0;
+ if (!page_is_ram(pfn))
+ return 1;
+ return 0;
+}