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drivers/char/hpet.c: allow user controlled mmap for user processes 

The CONFIG_HPET_MMAP Kconfig option exposes the memory map of the HPET
registers to userspace.  The Kconfig help points out that in some cases
this can be a security risk as some systems may erroneously configure the
map such that additional data is exposed to userspace.

This is a problem for distributions -- some users want the MMAP
functionality but it comes with a significant security risk.  In an effort
to mitigate this risk, and due to the low number of users of the MMAP
functionality, I've introduced a kernel parameter, hpet_mmap_enable, that
is required in order to actually have the HPET MMAP exposed.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Acked-by: Matt Wilson <msw@amazon.com>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Prarit Bhargava 2013-11-12 15:08:33 -08:00 committed by Linus Torvalds
parent 72403b4a0f
commit 3d035f5806
3 changed files with 35 additions and 6 deletions
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3
Documentation/kernel-parameters.txt
View File

@ -1070,6 +1070,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
VIA, nVidia)
verbose: show contents of HPET registers during setup
hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
On x86-64 and powerpc, this option can be specified

10
drivers/char/Kconfig
View File

@ -522,10 +522,16 @@ config HPET_MMAP
If you say Y here, user applications will be able to mmap
the HPET registers.
config HPET_MMAP_DEFAULT
bool "Enable HPET MMAP access by default"
default y
depends on HPET_MMAP
help
In some hardware implementations, the page containing HPET
registers may also contain other things that shouldn't be
exposed to the user. If this applies to your hardware,
say N here.
exposed to the user. This option selects the default (if
kernel parameter hpet_mmap is not set) user access to the
registers for applications that require it.
config HANGCHECK_TIMER
tristate "Hangcheck timer"

28
drivers/char/hpet.c
View File

@ -367,12 +367,29 @@ static unsigned int hpet_poll(struct file *file, poll_table * wait)
return 0;
}
#ifdef CONFIG_HPET_MMAP
#ifdef CONFIG_HPET_MMAP_DEFAULT
static int hpet_mmap_enabled = 1;
#else
static int hpet_mmap_enabled = 0;
#endif
static __init int hpet_mmap_enable(char *str)
{
get_option(&str, &hpet_mmap_enabled);
pr_info("HPET mmap %s\n", hpet_mmap_enabled ? "enabled" : "disabled");
return 1;
}
__setup("hpet_mmap", hpet_mmap_enable);
static int hpet_mmap(struct file *file, struct vm_area_struct *vma)
{
#ifdef CONFIG_HPET_MMAP
struct hpet_dev *devp;
unsigned long addr;
if (!hpet_mmap_enabled)
return -EACCES;
devp = file->private_data;
addr = devp->hd_hpets->hp_hpet_phys;
@ -381,10 +398,13 @@ static int hpet_mmap(struct file *file, struct vm_area_struct *vma)
vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
return vm_iomap_memory(vma, addr, PAGE_SIZE);
#else
return -ENOSYS;
#endif
}
#else
static int hpet_mmap(struct file *file, struct vm_area_struct *vma)
{
return -ENOSYS;
}
#endif
static int hpet_fasync(int fd, struct file *file, int on)
{