Subject: Re: [PATCH v5 11/11] kselftest: arm64: fake_sigreturn_misaligned_sp

From: Dave Martin <[email-masked]>
Date: Wed, 4 Sep 2019 12:49:44 +0100

On Mon, Sep 02, 2019 at 12:29:32pm +0100, Cristian Marussi wrote:
> Add a simple fake_sigreturn testcase which places a valid sigframe on a
> non-16 bytes aligned SP. Expects a SIGSEGV on test PASS.
> 
> Signed-off-by: Cristian Marussi <[email-masked]>
> ---
> v3 --> v4
> - fix commit
> - use new fake_sigreturn misalig_bytes params
> - removed TODO
> - added test description
> ---
>  .../testcases/fake_sigreturn_misaligned_sp.c  | 37 +++++++++++++++++++
>  1 file changed, 37 insertions(+)
>  create mode 100644 tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_misaligned_sp.c
> 
> diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_misaligned_sp.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_misaligned_sp.c
> new file mode 100644
> index 000000000000..1e089e66f9f3
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_misaligned_sp.c
> @@ -0,0 +1,37 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 ARM Limited
> + *
> + * Place a fake sigframe on the stack at a misaligned SP: on sigreturn
> + * Kernel must spot this attempt and the test case is expected to be
> + * terminated via SEGV.
> + */
> +
> +#include <signal.h>
> +#include <ucontext.h>
> +
> +#include "test_signals_utils.h"
> +#include "testcases.h"
> +
> +struct fake_sigframe sf;
> +
> +static int fake_sigreturn_misaligned_run(struct tdescr *td,
> +					 siginfo_t *si, ucontext_t *uc)
> +{
> +	/* just to fill the ucontext_t with something real */
> +	if (!get_current_context(td, &sf.uc))
> +		return 1;
> +
> +	/* Forcing sigframe on misaligned SP (16 + 3) */
> +	fake_sigreturn(&sf, sizeof(sf), 3);

Can we add tests on the TODO list for other misalignments?

 a) 4 (i.e., __alignof__(struct _aarch64_ctx))
 b) 8 (i.e., sizeof(struct _aarch64_ctx))

This may help catch potential wrong-bitmask bugs in the kernel when
checking the alignment.  Similarly to my suggestion on patch 10, these
can go on the TODO list and added later (probably macro-ised).

For now, let's get this series settled as-is -- so, after responding to
nits:

Reviewed-by: Dave Martin <[email-masked]>

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