* [PATCH] mm/kasan: map KASAN zero page read only
@ 2016-01-06 15:54 ` Ard Biesheuvel
0 siblings, 0 replies; 10+ messages in thread
From: Ard Biesheuvel @ 2016-01-06 15:54 UTC (permalink / raw)
To: linux-mm, linux-arm-kernel, ryabinin.a.a, catalin.marinas, mingo
Cc: Ard Biesheuvel
The original x86_64-only version of KASAN mapped its zero page
read-only, but this got lost when the code was generalised and
ported to arm64, since, at the time, the PAGE_KERNEL_RO define
did not exist. It has been added to arm64 in the mean time, so
let's use it.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
mm/kasan/kasan_init.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/kasan/kasan_init.c b/mm/kasan/kasan_init.c
index 3f9a41cf0ac6..8726a92604ad 100644
--- a/mm/kasan/kasan_init.c
+++ b/mm/kasan/kasan_init.c
@@ -49,7 +49,7 @@ static void __init zero_pte_populate(pmd_t *pmd, unsigned long addr,
pte_t *pte = pte_offset_kernel(pmd, addr);
pte_t zero_pte;
- zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL);
+ zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL_RO);
zero_pte = pte_wrprotect(zero_pte);
while (addr + PAGE_SIZE <= end) {
--
2.5.0
--
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^ permalink raw reply related [flat|nested] 10+ messages in thread
* [PATCH] mm/kasan: map KASAN zero page read only
@ 2016-01-06 15:54 ` Ard Biesheuvel
0 siblings, 0 replies; 10+ messages in thread
From: Ard Biesheuvel @ 2016-01-06 15:54 UTC (permalink / raw)
To: linux-arm-kernel
The original x86_64-only version of KASAN mapped its zero page
read-only, but this got lost when the code was generalised and
ported to arm64, since, at the time, the PAGE_KERNEL_RO define
did not exist. It has been added to arm64 in the mean time, so
let's use it.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
mm/kasan/kasan_init.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/kasan/kasan_init.c b/mm/kasan/kasan_init.c
index 3f9a41cf0ac6..8726a92604ad 100644
--- a/mm/kasan/kasan_init.c
+++ b/mm/kasan/kasan_init.c
@@ -49,7 +49,7 @@ static void __init zero_pte_populate(pmd_t *pmd, unsigned long addr,
pte_t *pte = pte_offset_kernel(pmd, addr);
pte_t zero_pte;
- zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL);
+ zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL_RO);
zero_pte = pte_wrprotect(zero_pte);
while (addr + PAGE_SIZE <= end) {
--
2.5.0
^ permalink raw reply related [flat|nested] 10+ messages in thread
* Re: [PATCH] mm/kasan: map KASAN zero page read only
2016-01-06 15:54 ` Ard Biesheuvel
@ 2016-01-06 19:48 ` Andrey Ryabinin
-1 siblings, 0 replies; 10+ messages in thread
From: Andrey Ryabinin @ 2016-01-06 19:48 UTC (permalink / raw)
To: Ard Biesheuvel; +Cc: linux-mm, linux-arm-kernel, Catalin Marinas, mingo
2016-01-06 18:54 GMT+03:00 Ard Biesheuvel <ard.biesheuvel@linaro.org>:
> The original x86_64-only version of KASAN mapped its zero page
> read-only, but this got lost when the code was generalised and
> ported to arm64, since, at the time, the PAGE_KERNEL_RO define
> did not exist. It has been added to arm64 in the mean time, so
> let's use it.
>
Read-only wasn't lost. Just look at the next line:
zero_pte = pte_wrprotect(zero_pte);
PAGE_KERNEL_RO is not available on all architectures, thus it would be better
to not use it in generic code.
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
> mm/kasan/kasan_init.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/kasan/kasan_init.c b/mm/kasan/kasan_init.c
> index 3f9a41cf0ac6..8726a92604ad 100644
> --- a/mm/kasan/kasan_init.c
> +++ b/mm/kasan/kasan_init.c
> @@ -49,7 +49,7 @@ static void __init zero_pte_populate(pmd_t *pmd, unsigned long addr,
> pte_t *pte = pte_offset_kernel(pmd, addr);
> pte_t zero_pte;
>
> - zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL);
> + zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL_RO);
> zero_pte = pte_wrprotect(zero_pte);
>
> while (addr + PAGE_SIZE <= end) {
> --
> 2.5.0
>
--
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^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH] mm/kasan: map KASAN zero page read only
@ 2016-01-06 19:48 ` Andrey Ryabinin
0 siblings, 0 replies; 10+ messages in thread
From: Andrey Ryabinin @ 2016-01-06 19:48 UTC (permalink / raw)
To: linux-arm-kernel
2016-01-06 18:54 GMT+03:00 Ard Biesheuvel <ard.biesheuvel@linaro.org>:
> The original x86_64-only version of KASAN mapped its zero page
> read-only, but this got lost when the code was generalised and
> ported to arm64, since, at the time, the PAGE_KERNEL_RO define
> did not exist. It has been added to arm64 in the mean time, so
> let's use it.
>
Read-only wasn't lost. Just look at the next line:
zero_pte = pte_wrprotect(zero_pte);
PAGE_KERNEL_RO is not available on all architectures, thus it would be better
to not use it in generic code.
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
> mm/kasan/kasan_init.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/kasan/kasan_init.c b/mm/kasan/kasan_init.c
> index 3f9a41cf0ac6..8726a92604ad 100644
> --- a/mm/kasan/kasan_init.c
> +++ b/mm/kasan/kasan_init.c
> @@ -49,7 +49,7 @@ static void __init zero_pte_populate(pmd_t *pmd, unsigned long addr,
> pte_t *pte = pte_offset_kernel(pmd, addr);
> pte_t zero_pte;
>
> - zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL);
> + zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL_RO);
> zero_pte = pte_wrprotect(zero_pte);
>
> while (addr + PAGE_SIZE <= end) {
> --
> 2.5.0
>
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] mm/kasan: map KASAN zero page read only
2016-01-06 19:48 ` Andrey Ryabinin
@ 2016-01-06 20:18 ` Ard Biesheuvel
-1 siblings, 0 replies; 10+ messages in thread
From: Ard Biesheuvel @ 2016-01-06 20:18 UTC (permalink / raw)
To: Andrey Ryabinin; +Cc: linux-mm, linux-arm-kernel, Catalin Marinas, mingo
On 6 January 2016 at 20:48, Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:
> 2016-01-06 18:54 GMT+03:00 Ard Biesheuvel <ard.biesheuvel@linaro.org>:
>> The original x86_64-only version of KASAN mapped its zero page
>> read-only, but this got lost when the code was generalised and
>> ported to arm64, since, at the time, the PAGE_KERNEL_RO define
>> did not exist. It has been added to arm64 in the mean time, so
>> let's use it.
>>
>
> Read-only wasn't lost. Just look at the next line:
> zero_pte = pte_wrprotect(zero_pte);
>
> PAGE_KERNEL_RO is not available on all architectures, thus it would be better
> to not use it in generic code.
>
OK, I didn't see that. For some reason, it is not working for me on
arm64, though.
I will investigate.
--
Ard.
>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> ---
>> mm/kasan/kasan_init.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/kasan/kasan_init.c b/mm/kasan/kasan_init.c
>> index 3f9a41cf0ac6..8726a92604ad 100644
>> --- a/mm/kasan/kasan_init.c
>> +++ b/mm/kasan/kasan_init.c
>> @@ -49,7 +49,7 @@ static void __init zero_pte_populate(pmd_t *pmd, unsigned long addr,
>> pte_t *pte = pte_offset_kernel(pmd, addr);
>> pte_t zero_pte;
>>
>> - zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL);
>> + zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL_RO);
>> zero_pte = pte_wrprotect(zero_pte);
>>
>> while (addr + PAGE_SIZE <= end) {
>> --
>> 2.5.0
>>
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
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^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH] mm/kasan: map KASAN zero page read only
@ 2016-01-06 20:18 ` Ard Biesheuvel
0 siblings, 0 replies; 10+ messages in thread
From: Ard Biesheuvel @ 2016-01-06 20:18 UTC (permalink / raw)
To: linux-arm-kernel
On 6 January 2016 at 20:48, Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:
> 2016-01-06 18:54 GMT+03:00 Ard Biesheuvel <ard.biesheuvel@linaro.org>:
>> The original x86_64-only version of KASAN mapped its zero page
>> read-only, but this got lost when the code was generalised and
>> ported to arm64, since, at the time, the PAGE_KERNEL_RO define
>> did not exist. It has been added to arm64 in the mean time, so
>> let's use it.
>>
>
> Read-only wasn't lost. Just look at the next line:
> zero_pte = pte_wrprotect(zero_pte);
>
> PAGE_KERNEL_RO is not available on all architectures, thus it would be better
> to not use it in generic code.
>
OK, I didn't see that. For some reason, it is not working for me on
arm64, though.
I will investigate.
--
Ard.
>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> ---
>> mm/kasan/kasan_init.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/kasan/kasan_init.c b/mm/kasan/kasan_init.c
>> index 3f9a41cf0ac6..8726a92604ad 100644
>> --- a/mm/kasan/kasan_init.c
>> +++ b/mm/kasan/kasan_init.c
>> @@ -49,7 +49,7 @@ static void __init zero_pte_populate(pmd_t *pmd, unsigned long addr,
>> pte_t *pte = pte_offset_kernel(pmd, addr);
>> pte_t zero_pte;
>>
>> - zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL);
>> + zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL_RO);
>> zero_pte = pte_wrprotect(zero_pte);
>>
>> while (addr + PAGE_SIZE <= end) {
>> --
>> 2.5.0
>>
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] mm/kasan: map KASAN zero page read only
2016-01-06 20:18 ` Ard Biesheuvel
@ 2016-01-07 9:51 ` Catalin Marinas
-1 siblings, 0 replies; 10+ messages in thread
From: Catalin Marinas @ 2016-01-07 9:51 UTC (permalink / raw)
To: Ard Biesheuvel; +Cc: Andrey Ryabinin, linux-mm, mingo, linux-arm-kernel
On Wed, Jan 06, 2016 at 09:18:03PM +0100, Ard Biesheuvel wrote:
> On 6 January 2016 at 20:48, Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:
> > 2016-01-06 18:54 GMT+03:00 Ard Biesheuvel <ard.biesheuvel@linaro.org>:
> >> The original x86_64-only version of KASAN mapped its zero page
> >> read-only, but this got lost when the code was generalised and
> >> ported to arm64, since, at the time, the PAGE_KERNEL_RO define
> >> did not exist. It has been added to arm64 in the mean time, so
> >> let's use it.
> >>
> >
> > Read-only wasn't lost. Just look at the next line:
> > zero_pte = pte_wrprotect(zero_pte);
> >
> > PAGE_KERNEL_RO is not available on all architectures, thus it would be better
> > to not use it in generic code.
>
> OK, I didn't see that. For some reason, it is not working for me on
> arm64, though.
It's because the arm64 set_pte_at() doesn't bother checking for
!PTE_WRITE to set PTE_RDONLY when mapping kernel pages. It works fine
for user though. That's because usually all read-only kernel mappings
already have PTE_RDONLY set via PAGE_KERNEL_RO.
We may need to change the set_pte_at logic a bit to cover the above
case.
--
Catalin
--
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^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH] mm/kasan: map KASAN zero page read only
@ 2016-01-07 9:51 ` Catalin Marinas
0 siblings, 0 replies; 10+ messages in thread
From: Catalin Marinas @ 2016-01-07 9:51 UTC (permalink / raw)
To: linux-arm-kernel
On Wed, Jan 06, 2016 at 09:18:03PM +0100, Ard Biesheuvel wrote:
> On 6 January 2016 at 20:48, Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:
> > 2016-01-06 18:54 GMT+03:00 Ard Biesheuvel <ard.biesheuvel@linaro.org>:
> >> The original x86_64-only version of KASAN mapped its zero page
> >> read-only, but this got lost when the code was generalised and
> >> ported to arm64, since, at the time, the PAGE_KERNEL_RO define
> >> did not exist. It has been added to arm64 in the mean time, so
> >> let's use it.
> >>
> >
> > Read-only wasn't lost. Just look at the next line:
> > zero_pte = pte_wrprotect(zero_pte);
> >
> > PAGE_KERNEL_RO is not available on all architectures, thus it would be better
> > to not use it in generic code.
>
> OK, I didn't see that. For some reason, it is not working for me on
> arm64, though.
It's because the arm64 set_pte_at() doesn't bother checking for
!PTE_WRITE to set PTE_RDONLY when mapping kernel pages. It works fine
for user though. That's because usually all read-only kernel mappings
already have PTE_RDONLY set via PAGE_KERNEL_RO.
We may need to change the set_pte_at logic a bit to cover the above
case.
--
Catalin
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] mm/kasan: map KASAN zero page read only
2016-01-07 9:51 ` Catalin Marinas
@ 2016-01-07 10:01 ` Ard Biesheuvel
-1 siblings, 0 replies; 10+ messages in thread
From: Ard Biesheuvel @ 2016-01-07 10:01 UTC (permalink / raw)
To: Catalin Marinas; +Cc: Andrey Ryabinin, linux-mm, mingo, linux-arm-kernel
On 7 January 2016 at 10:51, Catalin Marinas <catalin.marinas@arm.com> wrote:
> On Wed, Jan 06, 2016 at 09:18:03PM +0100, Ard Biesheuvel wrote:
>> On 6 January 2016 at 20:48, Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:
>> > 2016-01-06 18:54 GMT+03:00 Ard Biesheuvel <ard.biesheuvel@linaro.org>:
>> >> The original x86_64-only version of KASAN mapped its zero page
>> >> read-only, but this got lost when the code was generalised and
>> >> ported to arm64, since, at the time, the PAGE_KERNEL_RO define
>> >> did not exist. It has been added to arm64 in the mean time, so
>> >> let's use it.
>> >>
>> >
>> > Read-only wasn't lost. Just look at the next line:
>> > zero_pte = pte_wrprotect(zero_pte);
>> >
>> > PAGE_KERNEL_RO is not available on all architectures, thus it would be better
>> > to not use it in generic code.
>>
>> OK, I didn't see that. For some reason, it is not working for me on
>> arm64, though.
>
> It's because the arm64 set_pte_at() doesn't bother checking for
> !PTE_WRITE to set PTE_RDONLY when mapping kernel pages. It works fine
> for user though. That's because usually all read-only kernel mappings
> already have PTE_RDONLY set via PAGE_KERNEL_RO.
>
> We may need to change the set_pte_at logic a bit to cover the above
> case.
>
Yes, that would be useful. I had an interesting dive down a rabbit
hole yesterday due to the fact that the kasan zero page (which backs a
substantial chunk of the shadow area) was getting written to by one
mapping, and reporting KAsan errors via another.
--
Ard.
--
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^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH] mm/kasan: map KASAN zero page read only
@ 2016-01-07 10:01 ` Ard Biesheuvel
0 siblings, 0 replies; 10+ messages in thread
From: Ard Biesheuvel @ 2016-01-07 10:01 UTC (permalink / raw)
To: linux-arm-kernel
On 7 January 2016 at 10:51, Catalin Marinas <catalin.marinas@arm.com> wrote:
> On Wed, Jan 06, 2016 at 09:18:03PM +0100, Ard Biesheuvel wrote:
>> On 6 January 2016 at 20:48, Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:
>> > 2016-01-06 18:54 GMT+03:00 Ard Biesheuvel <ard.biesheuvel@linaro.org>:
>> >> The original x86_64-only version of KASAN mapped its zero page
>> >> read-only, but this got lost when the code was generalised and
>> >> ported to arm64, since, at the time, the PAGE_KERNEL_RO define
>> >> did not exist. It has been added to arm64 in the mean time, so
>> >> let's use it.
>> >>
>> >
>> > Read-only wasn't lost. Just look at the next line:
>> > zero_pte = pte_wrprotect(zero_pte);
>> >
>> > PAGE_KERNEL_RO is not available on all architectures, thus it would be better
>> > to not use it in generic code.
>>
>> OK, I didn't see that. For some reason, it is not working for me on
>> arm64, though.
>
> It's because the arm64 set_pte_at() doesn't bother checking for
> !PTE_WRITE to set PTE_RDONLY when mapping kernel pages. It works fine
> for user though. That's because usually all read-only kernel mappings
> already have PTE_RDONLY set via PAGE_KERNEL_RO.
>
> We may need to change the set_pte_at logic a bit to cover the above
> case.
>
Yes, that would be useful. I had an interesting dive down a rabbit
hole yesterday due to the fact that the kasan zero page (which backs a
substantial chunk of the shadow area) was getting written to by one
mapping, and reporting KAsan errors via another.
--
Ard.
^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2016-01-07 10:01 UTC | newest]
Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-01-06 15:54 [PATCH] mm/kasan: map KASAN zero page read only Ard Biesheuvel
2016-01-06 15:54 ` Ard Biesheuvel
2016-01-06 19:48 ` Andrey Ryabinin
2016-01-06 19:48 ` Andrey Ryabinin
2016-01-06 20:18 ` Ard Biesheuvel
2016-01-06 20:18 ` Ard Biesheuvel
2016-01-07 9:51 ` Catalin Marinas
2016-01-07 9:51 ` Catalin Marinas
2016-01-07 10:01 ` Ard Biesheuvel
2016-01-07 10:01 ` Ard Biesheuvel
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