The pmd_leaf() is used to test a leaf mapped PMD, however, it misses
the PROT_NONE mapped PMD on arm64. Fix it. A real world issue [1]
caused by this was reported by Qian Cai.
Link: https://patchwork.kernel.org/comment/24798260/ [1]
Fixes: 8aa82df3c123 ("arm64: mm: add p?d_leaf() definitions")
Reported-by: Qian Cai <[email protected]>
Signed-off-by: Muchun Song <[email protected]>
---
arch/arm64/include/asm/pgtable.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 94e147e5456c..09eaae46a19b 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -535,7 +535,7 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
PMD_TYPE_TABLE)
#define pmd_sect(pmd) ((pmd_val(pmd) & PMD_TYPE_MASK) == \
PMD_TYPE_SECT)
-#define pmd_leaf(pmd) pmd_sect(pmd)
+#define pmd_leaf(pmd) (pmd_present(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT))
#define pmd_bad(pmd) (!pmd_table(pmd))
#define pmd_leaf_size(pmd) (pmd_cont(pmd) ? CONT_PMD_SIZE : PMD_SIZE)
--
2.11.0
On Mon, Apr 4, 2022 at 10:10 PM Aneesh Kumar K V
<[email protected]> wrote:
>
> On 4/4/22 5:10 PM, Muchun Song wrote:
> > On Mon, Apr 4, 2022 at 5:20 PM Will Deacon <[email protected]> wrote:
> >>
> >> On Sun, Apr 03, 2022 at 10:49:28AM +0800, Muchun Song wrote:
> >>> The pmd_leaf() is used to test a leaf mapped PMD, however, it misses
> >>> the PROT_NONE mapped PMD on arm64. Fix it. A real world issue [1]
> >>> caused by this was reported by Qian Cai.
> >>>
> >>> Link: https://patchwork.kernel.org/comment/24798260/ [1]
> >>> Fixes: 8aa82df3c123 ("arm64: mm: add p?d_leaf() definitions")
> >>> Reported-by: Qian Cai <[email protected]>
> >>> Signed-off-by: Muchun Song <[email protected]>
> >>> ---
> >>> arch/arm64/include/asm/pgtable.h | 2 +-
> >>> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> >>> index 94e147e5456c..09eaae46a19b 100644
> >>> --- a/arch/arm64/include/asm/pgtable.h
> >>> +++ b/arch/arm64/include/asm/pgtable.h
> >>> @@ -535,7 +535,7 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
> >>> PMD_TYPE_TABLE)
> >>> #define pmd_sect(pmd) ((pmd_val(pmd) & PMD_TYPE_MASK) == \
> >>> PMD_TYPE_SECT)
> >>> -#define pmd_leaf(pmd) pmd_sect(pmd)
> >>> +#define pmd_leaf(pmd) (pmd_present(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT))
> >>> #define pmd_bad(pmd) (!pmd_table(pmd))
> >>>
> >>> #define pmd_leaf_size(pmd) (pmd_cont(pmd) ? CONT_PMD_SIZE : PMD_SIZE)
> >>
> >> A bunch of the users of pmd_leaf() already check pmd_present() -- is it
> >> documented that we need to handle this check inside the macro? afaict x86
> >> doesn't do this either.
>
>
> ppc64 also doesn't do a pmd_present check.
>
> >>
> >
> > arm64 is different from x86 here. pmd_leaf() could return true for
> > the none pmd without pmd_present() check, the check of
> > pmd_present() aims to exclude the pmd_none() case. However,
> > it could work properly on x86 without pmd_present() or pmd_none().
> > So we don't see pmd_present() or pmd_none() check in pmd_leaf().
> > For this reason, I think this check is necessary.
> >
> > BTW, there are some users of pmd_leaf() (e.g. apply_to_pmd_range,
> > walk_pmd_range, ptdump_pmd_entry) which do not check pmd_present()
> > or pmd_none() before the call of pmd_leaf(). So it is also necessary
> > to add the check.
> >
>
>
> I would expect pmd_leaf check to return true, if the said pmd page table
> entry can point to a leaf page table entry which can also be a not
> present page table entry?
>
All right. In order to exclude the pmd_none() case. How about
the following code?
#define pmd_leaf(pmd) (pmd_val(pmd) && !(pmd_val(pmd) &
PMD_TABLE_BIT))
Thanks.
On 4/4/22 5:10 PM, Muchun Song wrote:
> On Mon, Apr 4, 2022 at 5:20 PM Will Deacon <[email protected]> wrote:
>>
>> On Sun, Apr 03, 2022 at 10:49:28AM +0800, Muchun Song wrote:
>>> The pmd_leaf() is used to test a leaf mapped PMD, however, it misses
>>> the PROT_NONE mapped PMD on arm64. Fix it. A real world issue [1]
>>> caused by this was reported by Qian Cai.
>>>
>>> Link: https://patchwork.kernel.org/comment/24798260/ [1]
>>> Fixes: 8aa82df3c123 ("arm64: mm: add p?d_leaf() definitions")
>>> Reported-by: Qian Cai <[email protected]>
>>> Signed-off-by: Muchun Song <[email protected]>
>>> ---
>>> arch/arm64/include/asm/pgtable.h | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
>>> index 94e147e5456c..09eaae46a19b 100644
>>> --- a/arch/arm64/include/asm/pgtable.h
>>> +++ b/arch/arm64/include/asm/pgtable.h
>>> @@ -535,7 +535,7 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
>>> PMD_TYPE_TABLE)
>>> #define pmd_sect(pmd) ((pmd_val(pmd) & PMD_TYPE_MASK) == \
>>> PMD_TYPE_SECT)
>>> -#define pmd_leaf(pmd) pmd_sect(pmd)
>>> +#define pmd_leaf(pmd) (pmd_present(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT))
>>> #define pmd_bad(pmd) (!pmd_table(pmd))
>>>
>>> #define pmd_leaf_size(pmd) (pmd_cont(pmd) ? CONT_PMD_SIZE : PMD_SIZE)
>>
>> A bunch of the users of pmd_leaf() already check pmd_present() -- is it
>> documented that we need to handle this check inside the macro? afaict x86
>> doesn't do this either.
ppc64 also doesn't do a pmd_present check.
>>
>
> arm64 is different from x86 here. pmd_leaf() could return true for
> the none pmd without pmd_present() check, the check of
> pmd_present() aims to exclude the pmd_none() case. However,
> it could work properly on x86 without pmd_present() or pmd_none().
> So we don't see pmd_present() or pmd_none() check in pmd_leaf().
> For this reason, I think this check is necessary.
>
> BTW, there are some users of pmd_leaf() (e.g. apply_to_pmd_range,
> walk_pmd_range, ptdump_pmd_entry) which do not check pmd_present()
> or pmd_none() before the call of pmd_leaf(). So it is also necessary
> to add the check.
>
I would expect pmd_leaf check to return true, if the said pmd page table
entry can point to a leaf page table entry which can also be a not
present page table entry?
-aneesh