On 13/08/2019 17:26, Dave Martin wrote:
> 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
Ok
>
>> 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?
>
Ok
>> +#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
>
ok.
>> + */
>> + 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;
>> +}
>
I'll convert to use new helper get_starting_head() to make space in __reserved.
> [...]
>
> Otherwise looks reasonable.
>
> Cheers
> ---Dave
Cheers
Cristian
>
