On Tue, 15 Apr 2025 at 15:10, 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+0x14/0x1c
Only 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
This looks good to me -- we've hit what's effectively the same issue on other architectures with this test, with similar resolutions.
Reviewed-by: David Gow davidgow@google.com
I'm happy to have this (and the following path) go in via the KUnit tree, but if you'd rather have it go via MIPS, that's fine, too. (The qemu_configs won't generate any merge conflicts.)
-- David
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;
/* 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