[PATCH] selftests/powerpc: Add a test of SEGV error behaviour

[John Sperbeck]

On Tue, Jan 2, 2018 at 3:03 AM, Michael Ellerman <mpe at ellerman.id.au> wrote:
> Add a test case of the error code reported when we take a SEGV on a
> mapped but inaccessible area. We broke this recently.
>
> Based on a test case from John Sperbeck <jsperbeck at google.com>.
>
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
> ---
>  tools/testing/selftests/powerpc/mm/.gitignore    |  3 +-
>  tools/testing/selftests/powerpc/mm/Makefile      |  2 +-
>  tools/testing/selftests/powerpc/mm/segv_errors.c | 78 ++++++++++++++++++++++++
>  3 files changed, 81 insertions(+), 2 deletions(-)
>  create mode 100644 tools/testing/selftests/powerpc/mm/segv_errors.c
>
> diff --git a/tools/testing/selftests/powerpc/mm/.gitignore b/tools/testing/selftests/powerpc/mm/.gitignore
> index e715a3f2fbf4..7d7c42ed6de9 100644
> --- a/tools/testing/selftests/powerpc/mm/.gitignore
> +++ b/tools/testing/selftests/powerpc/mm/.gitignore
> @@ -1,4 +1,5 @@
>  hugetlb_vs_thp_test
>  subpage_prot
>  tempfile
> -prot_sao
> \ No newline at end of file
> +prot_sao
> +segv_errors
> \ No newline at end of file
> diff --git a/tools/testing/selftests/powerpc/mm/Makefile b/tools/testing/selftests/powerpc/mm/Makefile
> index bf315bcbe663..8ebbe96d80a8 100644
> --- a/tools/testing/selftests/powerpc/mm/Makefile
> +++ b/tools/testing/selftests/powerpc/mm/Makefile
> @@ -2,7 +2,7 @@
>  noarg:
>         $(MAKE) -C ../
>
> -TEST_GEN_PROGS := hugetlb_vs_thp_test subpage_prot prot_sao
> +TEST_GEN_PROGS := hugetlb_vs_thp_test subpage_prot prot_sao segv_errors
>  TEST_GEN_FILES := tempfile
>
>  include ../../lib.mk
> diff --git a/tools/testing/selftests/powerpc/mm/segv_errors.c b/tools/testing/selftests/powerpc/mm/segv_errors.c
> new file mode 100644
> index 000000000000..06ae76ee3ea1
> --- /dev/null
> +++ b/tools/testing/selftests/powerpc/mm/segv_errors.c
> @@ -0,0 +1,78 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Copyright 2017 John Sperbeck
> + *
> + * Test that an access to a mapped but inaccessible area causes a SEGV and
> + * reports si_code == SEGV_ACCERR.
> + */
> +
> +#include <stdbool.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <signal.h>
> +#include <sys/mman.h>
> +#include <assert.h>
> +#include <ucontext.h>
> +
> +#include "utils.h"
> +
> +static bool faulted;
> +static int si_code;
> +
> +static void segv_handler(int n, siginfo_t *info, void *ctxt_v)
> +{
> +       ucontext_t *ctxt = (ucontext_t *)ctxt_v;
> +       struct pt_regs *regs = ctxt->uc_mcontext.regs;
> +
> +       faulted = true;
> +       si_code = info->si_code;
> +       regs->nip += 4;
> +}
> +
> +int test_segv_errors(void)
> +{
> +       struct sigaction act = {
> +               .sa_sigaction = segv_handler,
> +               .sa_flags = SA_SIGINFO,
> +       };
> +       char c, *p = NULL;
> +
> +       p = mmap(NULL, getpagesize(), 0, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
> +       FAIL_IF(p == MAP_FAILED);
> +
> +       FAIL_IF(sigaction(SIGSEGV, &act, NULL) != 0);
> +
> +       faulted = false;
> +       si_code = 0;
> +
> +       /*
> +        * We just need a compiler barrier, but mb() works and has the nice
> +        * property of being easy to spot in the disassembly.
> +        */
> +       mb();
> +       c = *p;
> +       mb();
> +
> +       FAIL_IF(!faulted);
> +       FAIL_IF(si_code != SEGV_ACCERR);
> +
> +       faulted = false;
> +       si_code = 0;
> +
> +       mb();
> +       *p = c;
> +       mb();
> +
> +       FAIL_IF(!faulted);
> +       FAIL_IF(si_code != SEGV_ACCERR);
> +
> +       return 0;
> +}
> +
> +int main(void)
> +{
> +       return test_harness(test_segv_errors, "segv_errors");
> +}
> --
> 2.14.3
>

Looks good to me.

Acked-by: John Sperbeck <jsperbeck at google.com>