On Mon, Apr 14, 2025 at 05:32:47PM +0800, Huacai Chen wrote:
Hi, Thomas,
On Mon, Apr 14, 2025 at 4:29 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 vdso 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+0x14/0x1cSigned-off-by: Thomas Weißschuh thomas.weissschuh@linutronix.de
arch/mips/kernel/process.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c index b630604c577f9ff3f2493b0f254363e499c8318c..66343cb6c1737c4217ddd8a2c3ca244fac0ef8a5 100644 --- a/arch/mips/kernel/process.c +++ b/arch/mips/kernel/process.c @@ -690,9 +690,11 @@ 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 think the below code should also exist only when VDSO exists.
if (current->flags & PF_RANDOMIZE) top -= VDSO_RANDOMIZE_SIZE;
Good point, thanks. I'll move that up into the same new conditional block.
Huacai
/* Space for cache colour alignment */ if (cpu_has_dc_aliases)-- 2.49.0