On Thu, 25 Jul 2024 at 11:03, Will Deacon <will@xxxxxxxxxx> wrote: > > 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@xxxxxxx> > Cc: Ard Biesheuvel <ardb@xxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Link: https://lore.kernel.org/r/50360968-13fb-4e6f-8f52-1725b3177215@xxxxxxxxxxxxx > Fixes: 0dd4f60a2c76 ("arm64: mm: Add support for folding PUDs at runtime") > Reported-by: Asahi Lina <lina@xxxxxxxxxxxxx> > Signed-off-by: Will Deacon <will@xxxxxxxxxx> > --- > arch/arm64/include/asm/pgtable.h | 22 ++++++++++++++++++++++ > 1 file changed, 22 insertions(+) > Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
