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 can verify that their systems are secure, but it comes with a significant security risk for those who do not want the functionality. 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 <pra...@redhat.com> Cc: Clemens Ladisch <clem...@ladisch.de> --- Documentation/kernel-parameters.txt | 3 +++ drivers/char/hpet.c | 20 ++++++++++++++++++-- 2 files changed, 21 insertions(+), 2 deletions(-) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index e567af3..dbf0d81 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -962,6 +962,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted. VIA, nVidia) verbose: show contents of HPET registers during setup + hpet_mmap_enable [X86, HPET_MMAP] option to expose HPET MMAP to + userspace. By default this is disabled. + 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/hpet.c b/drivers/char/hpet.c index e3f9a99..de770ab 100644 --- a/drivers/char/hpet.c +++ b/drivers/char/hpet.c @@ -367,12 +367,25 @@ static unsigned int hpet_poll(struct file *file, poll_table * wait) return 0; } +#ifdef CONFIG_HPET_MMAP +static int hpet_mmap_enabled; + +static __init int hpet_mmap_enable(char *str) +{ + pr_info(KERN_INFO "HPET MMAP enabled\n"); + hpet_mmap_enabled = 1; + return 1; +} +__setup("hpet_mmap_enable", 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 +406,13 @@ 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/