Messages in this thread Patch in this message | | | Date | Sat, 26 Apr 2008 11:32:12 -0700 | From | Venki Pallipadi <> | Subject | Re: [git pull] x86 PAT changes |
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On Sat, Apr 26, 2008 at 10:15:33AM -0700, Linus Torvalds wrote: > > > On Sat, 26 Apr 2008, Pallipadi, Venkatesh wrote: > > > > Agreed that NONPROMISC_DEVMEM is not really needed for read/write. But, > > we will still need it for /dev/mem. > > If so, just disable it unconditionally for mmap. > > As mentioned, that's really just a return to original Linux /dev/mmap > semantics: long ago (well, not _that_ long ago) we never used to be able > to mmap() normal kernel memory, because the page counts would get screwed > up on pages that weren't marked PG_Reserved. > > So the traditional Linux behavior for mmap() on /dev/mem was always to > only allow it on memory that either had no "struct page *" backing at all, > or that was marked PG_Reserved (ie the ISA hole ay 640k-1M and things like > the BIOS tables etc). > > Going back to that doesn't sound horrible. >
OK. Below is the quick to disable /dev/mem mmap of RAM with PAT. This should go along with Ingo's patch that removes PAT dependency on NONPROMISC_DEVMEM. It makes things safer and eliminates aliasing. Still somewhat unclean as the range_is_allowed is duplicated. And also, just compile tested right now.
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
--- arch/x86/mm/pat.c | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+)
Index: linux-2.6/arch/x86/mm/pat.c =================================================================== --- linux-2.6.orig/arch/x86/mm/pat.c 2008-04-26 09:34:31.000000000 -0700 +++ linux-2.6/arch/x86/mm/pat.c 2008-04-26 11:25:57.000000000 -0700 @@ -16,6 +16,7 @@ #include <asm/msr.h> #include <asm/tlbflush.h> #include <asm/processor.h> +#include <asm/page.h> #include <asm/pgtable.h> #include <asm/pat.h> #include <asm/e820.h> @@ -477,6 +478,33 @@ pgprot_t phys_mem_access_prot(struct fil return vma_prot; } +#ifdef CONFIG_NONPROMISC_DEVMEM +/* This check is done in drivers/char/mem.c in case of NONPROMISC_DEVMEM*/ +static inline int range_is_allowed(unsigned long pfn, unsigned long size) +{ + return 1; +} +#else +static inline int range_is_allowed(unsigned long pfn, unsigned long size) +{ + u64 from = ((u64)pfn) << PAGE_SHIFT; + u64 to = from + size; + u64 cursor = from; + + while (cursor < to) { + if (!devmem_is_allowed(pfn)) { + printk(KERN_INFO + "Program %s tried to access /dev/mem between %Lx->%Lx.\n", + current->comm, from, to); + return 0; + } + cursor += PAGE_SIZE; + pfn++; + } + return 1; +} +#endif /* CONFIG_NONPROMISC_DEVMEM */ + int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn, unsigned long size, pgprot_t *vma_prot) { @@ -485,6 +513,9 @@ int phys_mem_access_prot_allowed(struct unsigned long ret_flags; int retval; + if (!range_is_allowed(pfn, size)) + return 0; + if (file->f_flags & O_SYNC) { flags = _PAGE_CACHE_UC; }
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