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>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a75a70a1f1e8e9b300c58a9d1b221b14d7a5216c..be74638521cce994324b09be2c5b40c920f290fd 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1068,6 +1068,9 @@ 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

diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 14219972c745ae6f31636e6e6bd0e89335f22c08..fa3243d71c76d0b9f14dde9066a2bff60a18165c 100644 (file)
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -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"

diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
index 448ce5e29c561bcf4fb8d1a6d3013fb6339e69be..fa7d9aef16197dd1fdc59782d853b784df795ead 100644 (file)
--- a/drivers/char/hpet.c
+++ b/drivers/char/hpet.c
@@ -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
+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)
 {