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Message-Id: <20250415-kunit-mips-v3-1-4ec2461b5a7e@linutronix.de>
Date: Tue, 15 Apr 2025 09:10:06 +0200
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
Brendan Higgins <brendan.higgins@...ux.dev>,
David Gow <davidgow@...gle.com>, Rae Moar <rmoar@...gle.com>,
Huacai Chen <chenhuacai@...nel.org>
Cc: linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com,
Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: [PATCH v3 1/2] MIPS: Don't crash in stack_top() for tasks without
ABI or vDSO
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@...utronix.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;
+
+ /* 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
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