On Fri, Aug 02, 2019 at 06:02:59PM +0100, Cristian Marussi wrote:
> Added a simple fake_sigreturn testcase which builds a ucontext_t
Add
> with a badly sized header that causes a overrun in the __reserved
> area and place it onto the stack. Expects a SIGSEGV on test PASS.
>
> Signed-off-by: Cristian Marussi <cristian.marussi@xxxxxxx>
> ---
> .../arm64/signal/testcases/.gitignore | 1 +
> .../testcases/fake_sigreturn_bad_size.c | 85 +++++++++++++++++++
> 2 files changed, 86 insertions(+)
> create mode 100644 tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_size.c
>
> diff --git a/tools/testing/selftests/arm64/signal/testcases/.gitignore b/tools/testing/selftests/arm64/signal/testcases/.gitignore
> index 94f9baaf638c..3408e0f5ba98 100644
> --- a/tools/testing/selftests/arm64/signal/testcases/.gitignore
> +++ b/tools/testing/selftests/arm64/signal/testcases/.gitignore
> @@ -8,3 +8,4 @@ fake_sigreturn_bad_magic
> fake_sigreturn_bad_size_for_magic0
> fake_sigreturn_missing_fpsimd
> fake_sigreturn_duplicated_fpsimd
> +fake_sigreturn_bad_size
> diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_size.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_size.c
> new file mode 100644
> index 000000000000..1467fb534d8b
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_size.c
> @@ -0,0 +1,85 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (C) 2019 ARM Limited */
> +
signal.h?
> +#include <stdio.h>
> +#include <ucontext.h>
> +
> +#include "test_signals_utils.h"
> +#include "testcases.h"
> +
> +struct fake_sigframe sf;
> +
> +#define MIN_SZ_ALIGN 16
> +
> +static int fake_sigreturn_bad_size_run(struct tdescr *td,
> + siginfo_t *si, ucontext_t *uc)
> +{
> + size_t resv_sz, need_sz, offset;
> + struct _aarch64_ctx *shead = GET_SF_RESV_HEAD(sf), *head;
> +
> + /* just to fill the ucontext_t with something real */
> + if (!get_current_context(td, &sf.uc))
> + return 1;
> +
> + resv_sz = GET_SF_RESV_SIZE(sf);
> + /*
> + * find the terminator, preserving existing headers
> + * and verify amount of spare room in __reserved area.
> + */
> + head = get_terminator(shead, resv_sz, &offset);
> + /*
> + * try stripping extra_context header when low on space:
> + * we need at least for the bad sized esr_context.
double space
> + */
> + need_sz = HDR_SZ + sizeof(struct esr_context);
> + if (head && resv_sz - offset < need_sz) {
> + fprintf(stderr, "Low on space:%zd. Discarding extra_context.\n",
> + resv_sz - offset);
> + head = get_header(shead, EXTRA_MAGIC, resv_sz, &offset);
> + }
> + /* just give up and timeout if still not enough space */
> + if (head && resv_sz - offset >= need_sz) {
> + fprintf(stderr, "Mangling template header. Spare space:%zd\n",
> + resv_sz - offset);
> + /*
> + * Use an esr_context to build a fake header with a
> + * size greater then the free __reserved area minus HDR_SZ;
> + * using ESR_MAGIC here since it is not checked for size nor
> + * is limited to one instance.
> + *
> + * At first inject an additional normal esr_context
> + */
> + head->magic = ESR_MAGIC;
> + head->size = sizeof(struct esr_context);
> + /* and terminate properly */
> + write_terminator_record(GET_RESV_NEXT_HEAD(head));
> + ASSERT_GOOD_CONTEXT(&sf.uc);
> +
> + /*
> + * now mess with fake esr_context size: leaving less space than
> + * neededwhile keeping size value 16-aligned
> + *
> + * It must trigger a SEGV from Kernel on:
> + *
> + * resv_sz - offset < sizeof(*head)
> + */
> + /* at first set the maximum good 16-aligned size */
> + head->size = (resv_sz - offset - need_sz + MIN_SZ_ALIGN) & ~0xfUL;
> + /* plus a bit more of 16-aligned sized stuff */
> + head->size += MIN_SZ_ALIGN;
> + /* and terminate properly */
> + write_terminator_record(GET_RESV_NEXT_HEAD(head));
> + ASSERT_BAD_CONTEXT(&sf.uc);
> + fake_sigreturn(&sf, sizeof(sf), 16);
> + }
> +
> + return 1;
> +}
[...]
Otherwise looks reasonable.
Cheers
---Dave
