Messages in this thread | | | Date | Mon, 21 Nov 2022 18:16:37 +0000 | From | Will Deacon <> | Subject | Re: [PATCH v2 2/2] arm64/mm: fix incorrect file_map_count for invalid pmd/pud |
| |
On Mon, Nov 21, 2022 at 11:15:49AM +0800, Liu Shixin wrote: > On 2022/11/18 22:34, Will Deacon wrote: > > On Thu, Nov 17, 2022 at 03:56:02PM +0800, Liu Shixin wrote: > >> The page table check trigger BUG_ON() unexpectedly when split hugepage: > >> > >> ------------[ cut here ]------------ > >> kernel BUG at mm/page_table_check.c:119! > >> Internal error: Oops - BUG: 00000000f2000800 [#1] SMP > >> Dumping ftrace buffer: > >> (ftrace buffer empty) > >> Modules linked in: > >> CPU: 7 PID: 210 Comm: transhuge-stres Not tainted 6.1.0-rc3+ #748 > >> Hardware name: linux,dummy-virt (DT) > >> pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) > >> pc : page_table_check_set.isra.0+0x398/0x468 > >> lr : page_table_check_set.isra.0+0x1c0/0x468 > >> [...] > >> Call trace: > >> page_table_check_set.isra.0+0x398/0x468 > >> __page_table_check_pte_set+0x160/0x1c0 > >> __split_huge_pmd_locked+0x900/0x1648 > >> __split_huge_pmd+0x28c/0x3b8 > >> unmap_page_range+0x428/0x858 > >> unmap_single_vma+0xf4/0x1c8 > >> zap_page_range+0x2b0/0x410 > >> madvise_vma_behavior+0xc44/0xe78 > >> do_madvise+0x280/0x698 > >> __arm64_sys_madvise+0x90/0xe8 > >> invoke_syscall.constprop.0+0xdc/0x1d8 > >> do_el0_svc+0xf4/0x3f8 > >> el0_svc+0x58/0x120 > >> el0t_64_sync_handler+0xb8/0xc0 > >> el0t_64_sync+0x19c/0x1a0 > >> [...] > >> > >> On arm64, pmd_leaf() will return true even if the pmd is invalid due to > >> pmd_present_invalid() check. So in pmdp_invalidate() the file_map_count > >> will not only decrease once but also increase once. Then in set_pte_at(), > >> the file_map_count increase again, and so trigger BUG_ON() unexpectedly. > >> > >> Fix this problem by adding pmd_valid() in pmd_user_accessible_page(). > >> Moreover, add pud_valid() for pud_user_accessible_page() too. > >> > >> Fixes: 42b2547137f5 ("arm64/mm: enable ARCH_SUPPORTS_PAGE_TABLE_CHECK") > >> Reported-by: Denys Vlasenko <dvlasenk@redhat.com> > >> Signed-off-by: Liu Shixin <liushixin2@huawei.com> > >> Acked-by: Pasha Tatashin <pasha.tatashin@soleen.com> > >> --- > >> arch/arm64/include/asm/pgtable.h | 4 ++-- > >> 1 file changed, 2 insertions(+), 2 deletions(-) > >> > >> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > >> index edf6625ce965..3bc64199aa2e 100644 > >> --- a/arch/arm64/include/asm/pgtable.h > >> +++ b/arch/arm64/include/asm/pgtable.h > >> @@ -863,12 +863,12 @@ static inline bool pte_user_accessible_page(pte_t pte) > >> > >> static inline bool pmd_user_accessible_page(pmd_t pmd) > >> { > >> - return pmd_leaf(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd)); > >> + return pmd_valid(pmd) && pmd_leaf(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd)); > > Hmm, doesn't this have a funny interaction with PROT_NONE where the pmd is > > invalid but present? If you don't care about PROT_NONE, then you could just > > do: > > > > pmd_valid(pmd) && !pmd_table(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd)) > > > > but if you do care then you could do: > > > > pmd_leaf(pmd) && !pmd_present_invalid(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd)) > I prefer the latter. I will fix and resend later. > >> static inline bool pud_user_accessible_page(pud_t pud) > >> { > >> - return pud_leaf(pud) && pud_user(pud); > >> + return pud_valid(pud) && pud_leaf(pud) && pud_user(pud); > > Not caused by this patch, but why don't we have something like a > > pud_user_exec() check here like we do for the pte and pmd levels? > As far as I know, there is no user use the user executable pud on arm64, so didn't define pud_user_exec().
I can believe they don't get exposed to userspace at all, but exposing only as non-executable doesn't sound right. So I would have thought that either pud_user_accessible_page() would always return false or it would need to check for the executable case too.
Will
| |