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>

diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index dabf8cb7203b7bf601518a7fd3ae8c8b0f86af9c..da2e861dee1c3eb63cd31a5342561f869903acc5 100644 (file)
--- 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 b4b98a03ff987c5361156d09af8b3f99895b1a9b..b26721cf51bc977412df0801fe36128f3d71ac69 100644 (file)
--- 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 0c781f912f9f0bdf526861fe60afd895e7107419..87410f62b50186a49bbf686f2cee1ff6ecc60c2b 100644 (file)
--- 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 a4a4c6864f51814f6fbc3b90b3c59b04d71471b1..34011a11fbb35c3cbefafe87a191c4b5c0fbc9ae 100644 (file)
--- 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 (file)
index 0000000..c0d67c5
--- /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;
+}