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authorHugh Dickins <hughd@google.com>2023-07-23 14:17:55 -0700
committerAndrew Morton <akpm@linux-foundation.org>2023-07-27 13:07:04 -0700
commit8b1cb4a2e819a2e4851ceeba53563f4edf03a8cf (patch)
tree54a3599e5b0e719e6809920a79c18bee07a6b182 /mm
parentfa598952fac059054316dccb2213478ccb81a0d1 (diff)
mm/pagewalk: fix EFI_PGT_DUMP of espfix area
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@google.com Closes: https://lore.kernel.org/linux-mm/CABXGCsN3JqXckWO=V7p=FhPU1tK03RE1w9UE6xL5Y86SMk209w@mail.gmail.com/ 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@google.com> Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com> Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com> Cc: Bagas Sanjaya <bagasdotme@gmail.com> Cc: Laura Abbott <labbott@fedoraproject.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/pagewalk.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 64437105fe0d..2022333805d3 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -48,8 +48,11 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
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);