linux-kernel - [PATCH 1/5] lib: Add a generic version of devmem_is

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Message-Id: <20200709200552.1910298-2-palmer@dabbelt.com>
Date:   Thu,  9 Jul 2020 13:05:48 -0700
From:   Palmer Dabbelt <palmer@...belt.com>
To:         linux-riscv@...ts.infradead.org, zong.li@...ive.com
Cc:     linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>, aou@...s.berkeley.edu,
        gxt@....edu.cn, Arnd Bergmann <arnd@...db.de>,
        akpm@...ux-foundation.org, linus.walleij@...aro.org,
        rppt@...ux.ibm.com, mchehab+samsung@...nel.org,
        gregory.0xf0@...il.com, masahiroy@...nel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        bgolaszewski@...libre.com, tglx@...utronix.de, steve@....org,
        keescook@...omium.org, mcgrof@...nel.org, alex@...ti.fr,
        mark.rutland@....com, james.morse@....com,
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        krzk@...nel.org, willy@...radead.org, paulmck@...nel.org,
        pmladek@...e.com, glider@...gle.com, elver@...gle.com,
        davidgow@...gle.com, ardb@...nel.org, takahiro.akashi@...aro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-arch@...r.kernel.org,
        kernel-team@...roid.com, Palmer Dabbelt <palmerdabbelt@...gle.com>
Subject: [PATCH 1/5] lib: Add a generic version of devmem_is_allowed()

From: Palmer Dabbelt <palmerdabbelt@...gle.com>

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.

Signed-off-by: Palmer Dabbelt <palmerdabbelt@...gle.com>
---
 include/asm-generic/io.h |  4 ++++
 lib/Kconfig              |  4 ++++
 lib/Makefile             |  2 ++
 lib/devmem_is_allowed.c  | 27 +++++++++++++++++++++++++++
 4 files changed, 37 insertions(+)
 create mode 100644 lib/devmem_is_allowed.c

diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index 8b1e020e9a03..69e3db65fba0 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 df3f3da95990..3b1b6481e073 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -676,3 +676,7 @@ config GENERIC_LIB_CMPDI2
 
 config GENERIC_LIB_UCMPDI2
 	bool
+
+config GENERIC_LIB_DEVMEM_IS_ALLOWED
+	bool
+	select ARCH_HAS_DEVMEM_IS_ALLOWED
diff --git a/lib/Makefile b/lib/Makefile
index b1c42c10073b..554ef14f9be5 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -318,3 +318,5 @@ obj-$(CONFIG_OBJAGG) += objagg.o
 # KUnit tests
 obj-$(CONFIG_LIST_KUNIT_TEST) += list-test.o
 obj-$(CONFIG_LINEAR_RANGES_TEST) += test_linear_ranges.o
+
+obj-$(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;
+}
-- 
2.27.0.383.g050319c2ae-goog