Messages in this thread | | | From | Barry Song <> | Date | Thu, 22 Sep 2022 09:45:28 +1200 | Subject | Re: [PATCH] arm64/mm: fold check for KFENCE into can_set_direct_map() |
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On Thu, Sep 22, 2022 at 3:16 AM Mike Rapoport <rppt@kernel.org> wrote: > > Hi Barry, > > On Wed, Sep 21, 2022 at 09:00:28PM +1200, Barry Song wrote: > > On Wed, Sep 21, 2022 at 8:26 PM Mike Rapoport <rppt@kernel.org> wrote: > > > > > > From: Mike Rapoport <rppt@linux.ibm.com> > > > > > > KFENCE requires linear map to be mapped at page granularity, so that it > > > is possible to protect/unprotect single pages, just like with > > > rodata_full and DEBUG_PAGEALLOC. > > > > > > Instead of repating > > > > > > can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE) > > > > > > make can_set_direct_map() handle the KFENCE case. > > > > > > This also prevents potential false positives in kernel_page_present() > > > that may return true for non-present page if CONFIG_KFENCE is enabled. > > > > > > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> > > > --- > > > arch/arm64/mm/mmu.c | 8 ++------ > > > arch/arm64/mm/pageattr.c | 8 +++++++- > > > 2 files changed, 9 insertions(+), 7 deletions(-) > > > > > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > > > index e7ad44585f40..c5065abec55a 100644 > > > --- a/arch/arm64/mm/mmu.c > > > +++ b/arch/arm64/mm/mmu.c > > > @@ -535,7 +535,7 @@ static void __init map_mem(pgd_t *pgdp) > > > */ > > > BUILD_BUG_ON(pgd_index(direct_map_end - 1) == pgd_index(direct_map_end)); > > > > > > - if (can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE)) > > > + if (can_set_direct_map()) > > > flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; > > > > > > /* > > > @@ -1547,11 +1547,7 @@ int arch_add_memory(int nid, u64 start, u64 size, > > > > > > VM_BUG_ON(!mhp_range_allowed(start, size, true)); > > > > > > - /* > > > - * KFENCE requires linear map to be mapped at page granularity, so that > > > - * it is possible to protect/unprotect single pages in the KFENCE pool. > > > - */ > > > - if (can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE)) > > > + if (can_set_direct_map()) > > > flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; > > > > > > __create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start), > > > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c > > > index 64e985eaa52d..d107c3d434e2 100644 > > > --- a/arch/arm64/mm/pageattr.c > > > +++ b/arch/arm64/mm/pageattr.c > > > @@ -21,7 +21,13 @@ bool rodata_full __ro_after_init = IS_ENABLED(CONFIG_RODATA_FULL_DEFAULT_ENABLED > > > > > > bool can_set_direct_map(void) > > > { > > > - return rodata_full || debug_pagealloc_enabled(); > > > + /* > > > + * rodata_full, DEBUG_PAGEALLOC and KFENCE require linear map to be > > > + * mapped at page granularity, so that it is possible to > > > + * protect/unprotect single pages. > > > + */ > > > + return rodata_full || debug_pagealloc_enabled() || > > > + IS_ENABLED(CONFIG_KFENCE); > > > > might be irrelevant, i wonder if rodata_full is too strict as > > rodata_full is almost > > always true since RODATA_FULL_DEFAULT_ENABLED is default true. > > Not sure I follow. If either of these conditions is true the linear map > consists of base pages and it's possible to change attributes of each base > page. Whenever linear map contains block mapping, page attributes cannot be > modified.
Hi Mike, My question is irrelevant with your patch. It is more of another topic. i understand we need to protect read-only data of kernel, but it seems overly defensive. We are getting the whole linear mapping PTE-mapped.
/sys/kernel/debug# cat kernel_page_tables 0x0000000000000000-0xffff608000000000 17179705856G PGD 0xffff608000000000-0xffff60bf40000000 253G PUD 0xffff60bf40000000-0xffff60bf40200000 2M PTE RW NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60bf40200000-0xffff60bf41800000 22M PMD ro NX SHD AF NG BLK UXN MEM/NORMAL 0xffff60bf41800000-0xffff60bf41890000 576K PTE ro NX SHD AF NG UXN MEM/NORMAL 0xffff60bf41890000-0xffff60c04022e000 4171384K PTE RW NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c04022e000-0xffff60c04022f000 4K PTE ro NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c04022f000-0xffff60c042a3c000 41012K PTE RW NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c042a3c000-0xffff60c042a3d000 4K PTE ro NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c042a3d000-0xffff60c043431000 10192K PTE RW NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c043431000-0xffff60c043432000 4K PTE ro NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c043432000-0xffff60c0448e8000 21208K PTE RW NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c0448e8000-0xffff60c0448e9000 4K PTE ro NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c0448e9000-0xffff60c0448ed000 16K PTE RW NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c0448ed000-0xffff60c0448ee000 4K PTE ro NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c0448ee000-0xffff60c044a6b000 1524K PTE RW NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c044a6b000-0xffff60c044a6c000 4K PTE ro NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c044a6c000-0xffff60c044a74000 32K PTE RW NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c044a74000-0xffff60c044a75000 4K PTE ro NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c044a75000-0xffff60c044aaa000 212K PTE RW NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c044aaa000-0xffff60c044aab000 4K PTE ro NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c044aab000-0xffff60c053000000 234836K PTE RW NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c053000000-0xffff60c080000000 720M PMD 0xffff60c080000000-0xffff610000000000 254G PUD 0xffff610000000000-0xffff800000000000 31T PGD ---[ Linear Mapping end ]---
For example, for the below, 0xffff60c04022e000-0xffff60c04022f000 4K PTE ro NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c04022f000-0xffff60c042a3c000 41012K PTE RW NX SHD AF NG UXN MEM/NORMAL-TAGGED
41012K PTE is really big, don't we have a chance to make it block/cont-pte mapped by some alignment tricks such as,
0xffff60c04022e000-0xffff60c04022f000 4K PTE ro NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c04022e000-0xffff60c040230000 4K PTE RW NX SHD AF NG UXN MEM/NORMAL-TAGGED 0xffff60c040230000-0xffff60c040400000- 4K PTE CONT.. 0xffff60c040400000- 2MB PMD.....
> > And rodata_full might be false because > CONFIG_RODATA_FULL_DEFAULT_ENABLED was disabled at build time. > > > > } > > > > > > static int change_page_range(pte_t *ptep, unsigned long addr, void *data) > > > -- > > > 2.35.3 > > > > > > > Thanks > > Barry > > -- > Sincerely yours, > Mike.
Thanks Barry
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