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Subject[PATCH] /dev/mem: Add kernel config option to omit this device.
Date
Many systems don't need /dev/mem, so make it optional.
It saves some space on embedded systems.

Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
---
arch/x86/Kconfig.debug | 1 +
drivers/char/Kconfig | 10 ++++++++++
drivers/char/mem.c | 17 +++++++++++++++++
3 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index e46c214..a47825b 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -7,6 +7,7 @@ source "lib/Kconfig.debug"

config STRICT_DEVMEM
bool "Filter access to /dev/mem"
+ depends on DEVMEM
---help---
If this option is disabled, you allow userspace (root) access to all
of memory, including kernel and userspace memory. Accidental
diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 4364303..a2e462e 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -6,6 +6,16 @@ menu "Character devices"

source "drivers/tty/Kconfig"

+config DEVMEM
+ bool "/dev/mem virtual device support"
+ default y
+ help
+ Say Y here if you want to support the /dev/mem device.
+ Some X server drivers access the video hardware using this device.
+ Accessing hardware directly from user space can be useful in some
+ cases, but it is not without risks.
+ When in doubt, say "N".
+
config DEVKMEM
bool "/dev/kmem virtual device support"
default y
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index d6e9d08..97a35c2 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -87,6 +87,8 @@ void __weak unxlate_dev_mem_ptr(unsigned long phys, void *addr)
{
}

+#ifdef CONFIG_DEVMEM
+
/*
* This funcion reads the *physical* memory. The f_pos points directly to the
* memory location.
@@ -210,6 +212,10 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
return written;
}

+#endif
+
+#if defined(CONFIG_DEVMEM) || defined(CONFIG_DEVKMEM)
+
int __weak phys_mem_access_prot_allowed(struct file *file,
unsigned long pfn, unsigned long size, pgprot_t *vma_prot)
{
@@ -331,6 +337,8 @@ static int mmap_mem(struct file *file, struct vm_area_struct *vma)
return 0;
}

+#endif
+
#ifdef CONFIG_DEVKMEM
static int mmap_kmem(struct file *file, struct vm_area_struct *vma)
{
@@ -694,6 +702,7 @@ static loff_t null_lseek(struct file *file, loff_t offset, int orig)
return file->f_pos = 0;
}

+#if defined(CONFIG_DEVMEM) || defined(CONFIG_DEVKMEM) || defined(CONFIG_DEVPORT)
/*
* The memory devices use the full 32/64 bits of the offset, and so we cannot
* check against negative addresses: they are ok. The return value is weird,
@@ -726,11 +735,15 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
mutex_unlock(&file->f_path.dentry->d_inode->i_mutex);
return ret;
}
+#endif

+#if defined(CONFIG_DEVMEM) || defined(CONFIG_DEVKMEM) || \
+ defined(CONFIG_DEVPORT) || defined(CONFIG_CRASH_DUMP)
static int open_port(struct inode * inode, struct file * filp)
{
return capable(CAP_SYS_RAWIO) ? 0 : -EPERM;
}
+#endif

#define zero_lseek null_lseek
#define full_lseek null_lseek
@@ -740,6 +753,7 @@ static int open_port(struct inode * inode, struct file * filp)
#define open_kmem open_mem
#define open_oldmem open_mem

+#ifdef CONFIG_DEVMEM
static const struct file_operations mem_fops = {
.llseek = memory_lseek,
.read = read_mem,
@@ -748,6 +762,7 @@ static const struct file_operations mem_fops = {
.open = open_mem,
.get_unmapped_area = get_unmapped_area_mem,
};
+#endif

#ifdef CONFIG_DEVKMEM
static const struct file_operations kmem_fops = {
@@ -851,7 +866,9 @@ static const struct memdev {
const struct file_operations *fops;
struct backing_dev_info *dev_info;
} devlist[] = {
+#ifdef CONFIG_DEVMEM
[1] = { "mem", 0, &mem_fops, &directly_mappable_cdev_bdi },
+#endif
#ifdef CONFIG_DEVKMEM
[2] = { "kmem", 0, &kmem_fops, &directly_mappable_cdev_bdi },
#endif
--
1.7.7


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