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SubjectRe: [PATCH 5/5] keep /dev/kmem from triggering BUG_ON() with DEBUG_VIRTUAL
Some more compiler warnings. Btw, I'm building 32-bit only for now - no
64-bit testing yet.

On Wed, Apr 10, 2013 at 04:32:56PM -0700, Dave Hansen wrote:
>
> /dev/kmem can essentially be used to make the kernel call __pa()
> on any address. But, with DEBUG_VIRTUAL, we are now ensuring
> that when __pa() is only called on addresses for which its
> results are correct. For everything else, we BUG_ON().
>
> What this means is that a hapless /dev/kmem user can
> unintentionally make the kernel BUG_ON().
>
> This adds a function, is_kernel_linear_vaddr() to the /dev/kmem
> code to ensure that __pa() will not BUG_ON(). It will, instead,
> return an error up to the user.
>
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> ---
>
> linux.git-davehans/arch/x86/mm/pageattr.c | 19 +++++++++++++++++++
> linux.git-davehans/drivers/char/mem.c | 8 ++++++++
> linux.git-davehans/include/linux/mmdebug.h | 2 ++
> 3 files changed, 29 insertions(+)
>
> diff -puN arch/x86/mm/pageattr.c~make-devmem-work-on-highmem3b arch/x86/mm/pageattr.c
> --- linux.git/arch/x86/mm/pageattr.c~make-devmem-work-on-highmem3b 2013-04-10 16:23:45.780087708 -0700
> +++ linux.git-davehans/arch/x86/mm/pageattr.c 2013-04-10 16:23:45.786087714 -0700
> @@ -406,6 +406,25 @@ phys_addr_t slow_virt_to_phys(void *virt
> }
> EXPORT_SYMBOL_GPL(slow_virt_to_phys);
>
> +#ifdef CONFIG_DEBUG_VIRTUAL
> +int is_kernel_linear_vaddr(void *kernel_vaddr)
> +{
> + int err;
> + unsigned long pte_walk_paddr;
> + unsigned long linear_paddr = __pa_nodebug(kernel_vaddr);
> +
> + err = kernel_lookup_vaddr(kernel_vaddr, &pte_walk_paddr);

arch/x86/mm/pageattr.c: In function ‘is_kernel_linear_vaddr’:
arch/x86/mm/pageattr.c:416:2: warning: passing argument 2 of ‘kernel_lookup_vaddr’ from incompatible pointer type [enabled by default]
arch/x86/mm/pageattr.c:366:5: note: expected ‘phys_addr_t *’ but argument is of type ‘long unsigned int *’


> + /* if there is no pte, it can not be in the normal linear map */
> + if (err)
> + return 0;
> + /* is there is a pte which does not match the linear layout? */
> + if (pte_walk_paddr != linear_paddr)
> + return 0;
> +
> + return 1;
> +}
> +#endif /* CONFIG_DEBUG_VIRTUAL */
> +
> /*
> * Set the new pmd in all the pgds we know about:
> */
> diff -puN drivers/char/mem.c~make-devmem-work-on-highmem3b drivers/char/mem.c
> --- linux.git/drivers/char/mem.c~make-devmem-work-on-highmem3b 2013-04-10 16:23:45.781087709 -0700
> +++ linux.git-davehans/drivers/char/mem.c 2013-04-10 16:23:45.787087715 -0700
> @@ -357,6 +357,14 @@ static int mmap_kmem(struct file *file,
> if (!pfn_valid(pfn))
> return -EIO;
>
> + /*
> + * the __pa() calculation below only makes sense if the kernel's
> + * pagetables are set up in the way that __pa() expects. Otherwise,
> + * we are effectively mapping random memory in to place.
> + */
> + if (!is_kernel_linear_vaddr(kernel_vaddr))

Ditto:

drivers/char/mem.c:365:2: warning: passing argument 1 of ‘is_kernel_linear_vaddr’ makes pointer from integer without a cast [enabled by default]


> + return -EIO;
> +
> /* Turn a kernel-virtual address into a physical page frame */
> pfn = __pa(kernel_vaddr) >> PAGE_SHIFT;
>
> diff -puN include/linux/mmdebug.h~make-devmem-work-on-highmem3b include/linux/mmdebug.h
> --- linux.git/include/linux/mmdebug.h~make-devmem-work-on-highmem3b 2013-04-10 16:23:45.783087711 -0700
> +++ linux.git-davehans/include/linux/mmdebug.h 2013-04-10 16:23:45.787087715 -0700
> @@ -9,8 +9,10 @@
>
> #ifdef CONFIG_DEBUG_VIRTUAL
> #define VIRTUAL_BUG_ON(cond) BUG_ON(cond)
> +extern int is_kernel_linear_vaddr(void *kernel_vaddr);
> #else
> #define VIRTUAL_BUG_ON(cond) do { } while (0)
> +static inline int is_kernel_linear_vaddr(void *kernel_vaddr) { return 1; }a

In file included from include/linux/gfp.h:8:0,
from include/linux/mm.h:8,
from drivers/char/mem.c:11:
include/linux/mmdebug.h:12:12: note: expected ‘void *’ but argument is of type ‘long unsigned int’
In file included from include/linux/gfp.h:4:0,
from include/linux/mm.h:8,
from drivers/char/mem.c:11:
include/linux/mmzone.h:1187:6: warning: ‘pfn’ may be used uninitialized in this function [-Wuninitialized]
drivers/char/mem.c:340:16: note: ‘pfn’ was declared here

HTH.

--
Regards/Gruss,
Boris.

Sent from a fat crate under my desk. Formatting is fine.
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