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| author | Hugh Dickins <hughd@google.com> | 2023-07-23 14:17:55 -0700 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2023-07-27 13:07:04 -0700 |
| commit | 8b1cb4a2e819a2e4851ceeba53563f4edf03a8cf (patch) | |
| tree | 54a3599e5b0e719e6809920a79c18bee07a6b182 /mm/pagewalk.c | |
| parent | fa598952fac059054316dccb2213478ccb81a0d1 (diff) | |
| download | lwn-8b1cb4a2e819a2e4851ceeba53563f4edf03a8cf.tar.gz lwn-8b1cb4a2e819a2e4851ceeba53563f4edf03a8cf.zip | |
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/pagewalk.c')
| -rw-r--r-- | mm/pagewalk.c | 5 |
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); |