Re: [PATCH RFT v7 9/9] selftests/clone3: Test shadow stack support

[Mark Brown]

On Mon, Aug 05, 2024 at 08:54:54PM -0700, Kees Cook wrote:

>   # Running test 'Shadow stack on system with shadow stack'
>   # [5496] Trying clone3() with flags 0 (size 0)
>   # I am the parent (5496). My child's pid is 5505
>   # Child exited with signal 11
>   # [5496] clone3() with flags says: 11 expected 0
>   # [5496] Result (11) is different than expected (0)
>   not ok 20 Shadow stack on system with shadow stack

> The child segfaults immediately, it seems?

Does this help:

diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
index 1755fa21e6fb..27acbdf44c5f 100644
--- a/arch/x86/kernel/shstk.c
+++ b/arch/x86/kernel/shstk.c
@@ -198,13 +198,14 @@ int arch_shstk_post_fork(struct task_struct *t, struct kernel_clone_args *args)
 	 * the token 64-bit.
 	 */
 	struct mm_struct *mm;
-	unsigned long addr;
+	unsigned long addr, ssp;
 	u64 expected;
 	u64 val;
-	int ret = -EINVAL;;
+	int ret = -EINVAL;
 
-	addr = args->shadow_stack + args->shadow_stack_size - sizeof(u64);
-	expected = (addr - SS_FRAME_SIZE) | BIT(0);
+	ssp = args->shadow_stack + args->shadow_stack_size;
+	addr = ssp - SS_FRAME_SIZE;
+	expected = ssp | BIT(0);
 
 	mm = get_task_mm(t);
 	if (!mm)

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