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Will Deacon 78672d49d3 arm64: mm: Fix lockless walks with static and dynamic page-table folding

commit 36639013b3462c06ff8e3400a427f775b4fc97f5 upstream.

Lina reports random oopsen originating from the fast GUP code when
16K pages are used with 4-level page-tables, the fourth level being
folded at runtime due to lack of LPA2.

In this configuration, the generic implementation of
p4d_offset_lockless() will return a 'p4d_t *' corresponding to the
'pgd_t' allocated on the stack of the caller, gup_fast_pgd_range().
This is normally fine, but when the fourth level of page-table is folded
at runtime, pud_offset_lockless() will offset from the address of the
'p4d_t' to calculate the address of the PUD in the same page-table page.
This results in a stray stack read when the 'p4d_t' has been allocated
on the stack and can send the walker into the weeds.

Fix the problem by providing our own definition of p4d_offset_lockless()
when CONFIG_PGTABLE_LEVELS <= 4 which returns the real page-table
pointer rather than the address of the local stack variable.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/50360968-13fb-4e6f-8f52-1725b3177215@asahilina.net
Fixes: 0dd4f60a2c76 ("arm64: mm: Add support for folding PUDs at runtime")
Reported-by: Asahi Lina <lina@asahilina.net>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240725090345.28461-1-will@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2024-08-03 09:00:48 +02:00

alpha

mseal: wire up mseal syscall

2024-05-23 19:40:26 -07:00

arc

bpf-for-netdev

2024-05-27 16:26:30 -07:00

arm

ARM: Remove address checking for MMUless devices

2024-08-03 08:59:30 +02:00

arm64

arm64: mm: Fix lockless walks with static and dynamic page-table folding