On Thu, 25 Jul 2024 at 11:03, Will Deacon will@kernel.org 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@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 Signed-off-by: Will Deacon will@kernel.org
arch/arm64/include/asm/pgtable.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)
Reviewed-by: Ard Biesheuvel ardb@kernel.org