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>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 882a40d..9ca3e74 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1070,6 +1070,9 @@
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
diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 1421997..fa3243d 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -522,10 +522,16 @@
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"
diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
index dca5834..5d9c31d 100644
--- a/drivers/char/hpet.c
+++ b/drivers/char/hpet.c
@@ -367,12 +367,29 @@
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 @@
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)
{