| Message ID | 1452095687-18136-1-git-send-email-ard.biesheuvel@linaro.org |
|---|---|
| State | New |
| Headers | show |
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 >> _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/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. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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) {
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(-) -- 2.5.0 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel