Hi Huacai,
On Tue, Apr 15, 2025 at 04:47:31PM +0800, Huacai Chen wrote:
On Tue, Apr 15, 2025 at 3:10 PM Thomas Weißschuh thomas.weissschuh@linutronix.de wrote:
Not all tasks have an ABI associated or vDSO mapped, for example kthreads never do. If such a task ever ends up calling stack_top(), it will derefence the NULL ABI pointer and crash.
This can for example happen when using kunit:
mips_stack_top+0x28/0xc0 arch_pick_mmap_layout+0x190/0x220 kunit_vm_mmap_init+0xf8/0x138 __kunit_add_resource+0x40/0xa8 kunit_vm_mmap+0x88/0xd8 usercopy_test_init+0xb8/0x240 kunit_try_run_case+0x5c/0x1a8 kunit_generic_run_threadfn_adapter+0x28/0x50 kthread+0x118/0x240 ret_from_kernel_thread+0x14/0x1cOnly dereference the ABI point if it is set.
Also move the randomization adjustment into the same conditional.
Signed-off-by: Thomas Weißschuh thomas.weissschuh@linutronix.de
arch/mips/kernel/process.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c index b630604c577f9ff3f2493b0f254363e499c8318c..02aa6a04a21da437909eeac4f149155cc298f5b5 100644 --- a/arch/mips/kernel/process.c +++ b/arch/mips/kernel/process.c @@ -690,18 +690,20 @@ unsigned long mips_stack_top(void) }
/* Space for the VDSO, data page & GIC user page */
top -= PAGE_ALIGN(current->thread.abi->vdso->size);top -= PAGE_SIZE;top -= mips_gic_present() ? PAGE_SIZE : 0;
if (current->thread.abi) {top -= PAGE_ALIGN(current->thread.abi->vdso->size);top -= PAGE_SIZE;top -= mips_gic_present() ? PAGE_SIZE : 0;I'm not sure, but maybe this line has nothing to do with VDSO.
The GIC page is also used by vDSO. It is mapped into the process together with the regular vDSO pages in arch_setup_additional_pages(). They should only ever be there together.
Thomas
/* Space to randomize the VDSO base */if (current->flags & PF_RANDOMIZE)top -= VDSO_RANDOMIZE_SIZE;} /* Space for cache colour alignment */ if (cpu_has_dc_aliases) top -= shm_align_mask + 1;
/* Space to randomize the VDSO base */if (current->flags & PF_RANDOMIZE)top -= VDSO_RANDOMIZE_SIZE;return top;}
-- 2.49.0