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x86/mm/pageattr: Prevent PSE and GLOABL leftovers to confuse pmd/pte_present and pmd_huge

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Without this patch any kernel code that reads kernel memory in
non present kernel pte/pmds (as set by pageattr.c) will crash.

With this kernel code:

static struct page *crash_page;
static unsigned long *crash_address;
[..]
	crash_page = alloc_pages(GFP_KERNEL, 9);
	crash_address = page_address(crash_page);
	if (set_memory_np((unsigned long)crash_address, 1))
		printk("set_memory_np failure\n");
[..]

The kernel will crash if inside the "crash tool" one would try
to read the memory at the not present address.

crash> p crash_address
crash_address = $8 = (long unsigned int *) 0xffff88023c000000
crash> rd 0xffff88023c000000
[ *lockup* ]

The lockup happens because _PAGE_GLOBAL and _PAGE_PROTNONE
shares the same bit, and pageattr leaves _PAGE_GLOBAL set on a
kernel pte which is then mistaken as _PAGE_PROTNONE (so
pte_present returns true by mistake and the kernel fault then
gets confused and loops).

With THP the same can happen after we taught pmd_present to
check _PAGE_PROTNONE and _PAGE_PSE in commit
027ef6c878 ("mm: thp: fix pmd_present for
split_huge_page and PROT_NONE with THP").  THP has the same
problem with _PAGE_GLOBAL as the 4k pages, but it also has a
problem with _PAGE_PSE, which must be cleared too.

After the patch is applied copy_user correctly returns -EFAULT
and doesn't lockup anymore.

crash> p crash_address
crash_address = $9 = (long unsigned int *) 0xffff88023c000000
crash> rd 0xffff88023c000000
rd: read error: kernel virtual address: ffff88023c000000  type:
"64-bit KVADDR"

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Shaohua Li <shaohua.li@intel.com>
Cc: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andrea Arcangeli 2013-02-22 15:11:51 -08:00 committed by Ingo Molnar
parent 954f857187
commit a8aed3e075
1 changed files with 47 additions and 3 deletions
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50
arch/x86/mm/pageattr.c
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@ -444,6 +444,19 @@ try_preserve_large_page(pte_t *kpte, unsigned long address,
pgprot_val(req_prot) &= ~pgprot_val(cpa->mask_clr);
pgprot_val(req_prot) |= pgprot_val(cpa->mask_set);
/*
* Set the PSE and GLOBAL flags only if the PRESENT flag is
* set otherwise pmd_present/pmd_huge will return true even on
* a non present pmd. The canon_pgprot will clear _PAGE_GLOBAL
* for the ancient hardware that doesn't support it.
*/
if (pgprot_val(new_prot) & _PAGE_PRESENT)
pgprot_val(new_prot) |= _PAGE_PSE | _PAGE_GLOBAL;
else
pgprot_val(new_prot) &= ~(_PAGE_PSE | _PAGE_GLOBAL);
new_prot = canon_pgprot(new_prot);
/*
* old_pte points to the large page base address. So we need
* to add the offset of the virtual address:
@ -489,7 +502,7 @@ try_preserve_large_page(pte_t *kpte, unsigned long address,
* The address is aligned and the number of pages
* covers the full page.
*/
new_pte = pfn_pte(pte_pfn(old_pte), canon_pgprot(new_prot));
new_pte = pfn_pte(pte_pfn(old_pte), new_prot);
__set_pmd_pte(kpte, address, new_pte);
cpa->flags |= CPA_FLUSHTLB;
do_split = 0;
@ -540,16 +553,35 @@ static int split_large_page(pte_t *kpte, unsigned long address)
#ifdef CONFIG_X86_64
if (level == PG_LEVEL_1G) {
pfninc = PMD_PAGE_SIZE >> PAGE_SHIFT;
pgprot_val(ref_prot) |= _PAGE_PSE;
/*
* Set the PSE flags only if the PRESENT flag is set
* otherwise pmd_present/pmd_huge will return true
* even on a non present pmd.
*/
if (pgprot_val(ref_prot) & _PAGE_PRESENT)
pgprot_val(ref_prot) |= _PAGE_PSE;
else
pgprot_val(ref_prot) &= ~_PAGE_PSE;
}
#endif
/*
* Set the GLOBAL flags only if the PRESENT flag is set
* otherwise pmd/pte_present will return true even on a non
* present pmd/pte. The canon_pgprot will clear _PAGE_GLOBAL
* for the ancient hardware that doesn't support it.
*/
if (pgprot_val(ref_prot) & _PAGE_PRESENT)
pgprot_val(ref_prot) |= _PAGE_GLOBAL;
else
pgprot_val(ref_prot) &= ~_PAGE_GLOBAL;
/*
* Get the target pfn from the original entry:
*/
pfn = pte_pfn(*kpte);
for (i = 0; i < PTRS_PER_PTE; i++, pfn += pfninc)
set_pte(&pbase[i], pfn_pte(pfn, ref_prot));
set_pte(&pbase[i], pfn_pte(pfn, canon_pgprot(ref_prot)));
if (address >= (unsigned long)__va(0) &&
address < (unsigned long)__va(max_low_pfn_mapped << PAGE_SHIFT))
@ -659,6 +691,18 @@ repeat:
new_prot = static_protections(new_prot, address, pfn);
/*
* Set the GLOBAL flags only if the PRESENT flag is
* set otherwise pte_present will return true even on
* a non present pte. The canon_pgprot will clear
* _PAGE_GLOBAL for the ancient hardware that doesn't
* support it.
*/
if (pgprot_val(new_prot) & _PAGE_PRESENT)
pgprot_val(new_prot) |= _PAGE_GLOBAL;
else
pgprot_val(new_prot) &= ~_PAGE_GLOBAL;
/*
* We need to keep the pfn from the existing PTE,
* after all we're only going to change it's attributes