The patch titled
Subject: mm/pagewalk: fix EFI_PGT_DUMP of espfix area
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-pagewalk-fix-efi_pgt_dump-of-espfix-area.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-pagewalk-fix-efi_pgt_dump-of-espfix-area.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm/pagewalk: fix EFI_PGT_DUMP of espfix area
Date: Sun, 23 Jul 2023 14:17:55 -0700 (PDT)
Booting x86_64 with CONFIG_EFI_PGT_DUMP=y shows messages of the form
"mm/pgtable-generic.c:53: bad pmd (____ptrval____)(8000000100077061)".
EFI_PGT_DUMP dumps all of efi_mm, including the espfix area, which is set
up with pmd entries which fit the pmd_bad() check: so 0d940a9b270b warns
and clears those entries, which would ruin running Win16 binaries.
The failing pte_offset_map() stopped such a kernel from even booting,
until a few commits later be872f83bf57 changed the pagewalk to tolerate
that: but it needs to be even more careful, to not spoil those entries.
I might have preferred to change init_espfix_ap() not to use "bad" pmd
entries; or to leave them out of the efi_mm dump. But there is great
value in staying away from there, and a pagewalk check of address against
TASK_SIZE may protect from other such aberrations too.
Link: https://lkml.kernel.org/r/22bca736-4cab-9ee5-6a52-73a3b2bbe865@xxxxxxxxxx
Closes: https://lore.kernel.org/linux-mm/CABXGCsN3JqXckWO=V7p=FhPU1tK03RE1w9UE6xL5Y86SMk209w@xxxxxxxxxxxxxx/
Fixes: 0d940a9b270b ("mm/pgtable: allow pte_offset_map[_lock]() to fail")
Fixes: be872f83bf57 ("mm/pagewalk: walk_pte_range() allow for pte_offset_map()")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>
Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>
Cc: Bagas Sanjaya <bagasdotme@xxxxxxxxx>
Cc: Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/pagewalk.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/mm/pagewalk.c~mm-pagewalk-fix-efi_pgt_dump-of-espfix-area
+++ a/mm/pagewalk.c
@@ -48,8 +48,11 @@ static int walk_pte_range(pmd_t *pmd, un
if (walk->no_vma) {
/*
* pte_offset_map() might apply user-specific validation.
+ * Indeed, on x86_64 the pmd entries set up by init_espfix_ap()
+ * fit its pmd_bad() check (_PAGE_NX set and _PAGE_RW clear),
+ * and CONFIG_EFI_PGT_DUMP efi_mm goes so far as to walk them.
*/
- if (walk->mm == &init_mm)
+ if (walk->mm == &init_mm || addr >= TASK_SIZE)
pte = pte_offset_kernel(pmd, addr);
else
pte = pte_offset_map(pmd, addr);
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
tmpfs-fix-documentation-of-noswap-and-huge-mount-options.patch
shmem-minor-fixes-to-splice-read-implementation.patch
mm-pagewalk-fix-efi_pgt_dump-of-espfix-area.patch
mm-userfaultfd-add-new-uffdio_poison-ioctl-fix.patch
mm-pgtable-add-rcu_read_lock-and-rcu_read_unlocks.patch
mm-pgtable-add-pae-safety-to-__pte_offset_map.patch
arm-adjust_pte-use-pte_offset_map_nolock.patch
powerpc-assert_pte_locked-use-pte_offset_map_nolock.patch
powerpc-add-pte_free_defer-for-pgtables-sharing-page.patch
sparc-add-pte_free_defer-for-pte_t-pgtable_t.patch
s390-add-pte_free_defer-for-pgtables-sharing-page.patch
mm-pgtable-add-pte_free_defer-for-pgtable-as-page.patch
mm-khugepaged-retract_page_tables-without-mmap-or-vma-lock.patch
mm-khugepaged-collapse_pte_mapped_thp-with-mmap_read_lock.patch
mm-khugepaged-delete-khugepaged_collapse_pte_mapped_thps.patch
mm-delete-mmap_write_trylock-and-vma_try_start_write.patch
mm-pgtable-notes-on-pte_offset_map.patch
powerpc-assert_pte_locked-use-pte_offset_map_nolock-fix.patch
