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.
[v2]: Clemens suggested modifying the Kconfig help text and making the
default setting configurable.
[v3]: Fixed up Documentation and Kconfig entries, default now "Y"
[v4]: After testing, found that I need to modify CONFIG_HPET_MMAP_DEFAULT usage
Signed-off-by: Prarit Bhargava <pra...@redhat.com>
Cc: Clemens Ladisch <clem...@ladisch.de>
---
Documentation/kernel-parameters.txt | 4 ++++
drivers/char/Kconfig | 9 +++++++--
drivers/char/hpet.c | 25 +++++++++++++++++++++++--
3 files changed, 34 insertions(+), 4 deletions(-)
diff --git a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt
index e567af3..1444491 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -962,6 +962,10 @@ 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] option to expose HPET MMAP to
+ userspace. By default this is disabled. Values are
+ 0(disabled) or 1(enabled).
+
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 3bb6fa3..51b62a1 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -534,10 +534,15 @@ 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 user access
+ to the HPET 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 e3f9a99..b3ba043 100644
--- a/drivers/char/hpet.c
+++ b/drivers/char/hpet.c
@@ -367,12 +367,30 @@ 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(KERN_INFO "HPET MMAP %s\n",
+ hpet_mmap_enabled ? "disabled" : "enabled");
+ 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;
+
if (((vma->vm_end - vma->vm_start) != PAGE_SIZE) || vma->vm_pgoff)
return -EINVAL;
@@ -393,10 +411,13 @@ static int hpet_mmap(struct file *file, struct
vm_area_struct *vma)
}
return 0;
+}
#else
+static int hpet_mmap(struct file *file, struct vm_area_struct *vma)
+{
return -ENOSYS;
-#endif
}
+#endif
static int hpet_fasync(int fd, struct file *file, int on)
{
--
1.7.9.3
--
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