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powerpc/hugetlb: fix page rights verification in gup_hugepte() 

gup_hugepte() checks if pages are present and readable, and
when  'write' is set, also checks if the pages are writable.

Initially this was done by checking if _PAGE_PRESENT and
_PAGE_READ were set. In addition, _PAGE_WRITE was verified for write
accesses.

The problem is that we have to handle the three following cases:
1/ The target defines __PAGE_READ and __PAGE_WRITE
2/ The target defines __PAGE_RW
3/ The target defines __PAGE_RO

In case 1/, this is obvious
In case 2/, __PAGE_READ is defined as 0 and __PAGE_WRITE as __PAGE_RW
so it works as well.
But in case 3, __PAGE_RW is defined as 0, which means __PAGE_WRITE is 0
and then the test returns true (page writable) in all cases.

A first correction was attempted in commit 6b8cb66a6a ("powerpc: Fix
usage of _PAGE_RO in hugepage"), but that fix is wrong:
instead of checking that the page is writable when write is requested,
it checks that the page is NOT writable when write is NOT requested.

This patch adds a new pte_read() helper to check whether a page is
readable or not. This avoids handling all possible cases in
gup_hugepte().

Then gup_hugepte() is modified to use pte_present(), pte_read()
and pte_write() instead of the raw flags.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Christophe Leroy 2017-07-12 17:03:42 +02:00 committed by Michael Ellerman
parent 4cfac2f9c7
commit ca8afd4046
4 changed files with 10 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/powerpc/include/asm/book3s/32/pgtable.h
View File

@ -298,6 +298,7 @@ int map_kernel_page(unsigned long va, phys_addr_t pa, int flags);
/* Generic accessors to PTE bits */
static inline int pte_write(pte_t pte) { return !!(pte_val(pte) & _PAGE_RW);}
static inline int pte_read(pte_t pte) { return 1; }
static inline int pte_dirty(pte_t pte) { return !!(pte_val(pte) & _PAGE_DIRTY); }
static inline int pte_young(pte_t pte) { return !!(pte_val(pte) & _PAGE_ACCESSED); }
static inline int pte_special(pte_t pte) { return !!(pte_val(pte) & _PAGE_SPECIAL); }

5
arch/powerpc/include/asm/book3s/64/pgtable.h
View File

@ -410,6 +410,11 @@ static inline int pte_write(pte_t pte)
return __pte_write(pte) || pte_savedwrite(pte);
}
static inline int pte_read(pte_t pte)
{
return !!(pte_raw(pte) & cpu_to_be64(_PAGE_READ));
}
#define __HAVE_ARCH_PTEP_SET_WRPROTECT
static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr,
pte_t *ptep)

1
arch/powerpc/include/asm/nohash/pgtable.h
View File

@ -14,6 +14,7 @@ static inline int pte_write(pte_t pte)
{
return (pte_val(pte) & (_PAGE_RW | _PAGE_RO)) != _PAGE_RO;
}
static inline int pte_read(pte_t pte) { return 1; }
static inline int pte_dirty(pte_t pte) { return pte_val(pte) & _PAGE_DIRTY; }
static inline int pte_young(pte_t pte) { return pte_val(pte) & _PAGE_ACCESSED; }
static inline int pte_special(pte_t pte) { return pte_val(pte) & _PAGE_SPECIAL; }

15
arch/powerpc/mm/hugetlbpage.c
View File

@ -977,7 +977,6 @@ EXPORT_SYMBOL_GPL(__find_linux_pte_or_hugepte);
int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
unsigned long end, int write, struct page **pages, int *nr)
{
unsigned long mask;
unsigned long pte_end;
struct page *head, *page;
pte_t pte;
@ -988,18 +987,10 @@ int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
end = pte_end;
pte = READ_ONCE(*ptep);
mask = _PAGE_PRESENT | _PAGE_READ;
/*
* On some CPUs like the 8xx, _PAGE_RW hence _PAGE_WRITE is defined
* as 0 and _PAGE_RO has to be set when a page is not writable
*/
if (write)
mask |= _PAGE_WRITE;
else
mask |= _PAGE_RO;
if ((pte_val(pte) & mask) != mask)
if (!pte_present(pte) || !pte_read(pte))
return 0;
if (write && !pte_write(pte))
return 0;
/* hugepages are never "special" */