Hi
On 13/08/2019 17:25, Dave Martin wrote:
On Fri, Aug 02, 2019 at 06:02:55PM +0100, Cristian Marussi wrote:
Added a simple fake_sigreturn testcase which builds a ucontext_t
Add
Ok
with a bad magic header and place it onto the stack. Expects a SIGSEGV on test PASS. This commit also introduces a common utility assembly function to invoke a sigreturn using a fake provided sigframe.
Signed-off-by: Cristian Marussi cristian.marussi@arm.com
tools/testing/selftests/arm64/signal/Makefile | 2 +- .../testing/selftests/arm64/signal/signals.S | 64 +++++++++++++++++++ .../arm64/signal/test_signals_utils.h | 1 + .../arm64/signal/testcases/.gitignore | 1 + .../testcases/fake_sigreturn_bad_magic.c | 63 ++++++++++++++++++ 5 files changed, 130 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/arm64/signal/signals.S create mode 100644 tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c
diff --git a/tools/testing/selftests/arm64/signal/Makefile b/tools/testing/selftests/arm64/signal/Makefile index 8c8d08be4b0d..b3dcf315b5a4 100644 --- a/tools/testing/selftests/arm64/signal/Makefile +++ b/tools/testing/selftests/arm64/signal/Makefile @@ -80,7 +80,7 @@ endif # Common test-unit targets to build common-layout test-cases executables # Needs secondary expansion to properly include the testcase c-file in pre-reqs .SECONDEXPANSION: -$(PROGS): test_signals.c test_signals_utils.c testcases/testcases.c $$@.c test_signals.h test_signals_utils.h testcases/testcases.h +$(PROGS): test_signals.c test_signals_utils.c testcases/testcases.c signals.S $$@.c test_signals.h test_signals_utils.h testcases/testcases.h @if [ ! -d $(khdr_dir) ]; then \ echo -n "\n!!! WARNING: $(khdr_dir) NOT FOUND."; \ echo "===> Are you sure Kernel Headers have been installed properly ?\n"; \ diff --git a/tools/testing/selftests/arm64/signal/signals.S b/tools/testing/selftests/arm64/signal/signals.S new file mode 100644 index 000000000000..6262b877400b --- /dev/null +++ b/tools/testing/selftests/arm64/signal/signals.S @@ -0,0 +1,64 @@ +/*
- SPDX-License-Identifier: GPL-2.0
- Copyright (C) 2019 ARM Limited
- */
+#include <asm/unistd.h>
+.section ".rodata", "a"
The section name is not usually quoted in .section (though I guess it works).
Ok
+call_fmt:
- .asciz "Calling sigreturn with fake sigframe sized:%zd at calculated SP @%08lX\n"
+.text
+.globl fake_sigreturn
+/* fake_sigreturn x0:&sigframe, x1:sigframe_size, x2:alignment_SP */ +fake_sigreturn:
- mov x20, x0
- mov x21, x1
- mov x22, x2
- mov x23, sp
- /* create space on the stack for fake sigframe..."x22"-aligned */
- mov x0, #0
Why to we move 0 into x0? We clobber x0 again in the next instruction:
Yes unneeded.
- add x0, x21, x22
- sub x22, x22, #1
- bic x0, x0, x22
- sub x23, x23, x0
Can you explain the logic here? I'm not sure I understand what this is trying to do exactly.
The attempt is to make space on the stack for a x22-bytes-aligned sigframe of at least x21-bytes-size (assuming x22 is power-of-two):
- calculate the needed aligned space (sigframe_size + x22) & ~(x22 - 1) - calculate new SP in x23: x3 = sp - needed_aligned_space - later down... move SP to the calculated sp in x23 - copy the provided sigframe on such new SP
I notice you further modify this in patch 11 -- see my comments there, where I also suggest an alternative way of specifying a misaligned frame that might be simpler.
I've seen your comments on patch 11. I think I'll simplify that as you suggested: patch 11 was meant to add the capability to misalign the sigframe on the SP (which is needed in testcase contained in 11) but in fact is better if I move all of the simplified logic here.
- ldr x0, =call_fmt
- mov x1, x21
- mov x2, x23
- bl printf
- mov sp, x23
- /* now fill it with the provided content... */
- mov x0, sp
- mov x1, x20
- mov x2, x21
- bl memcpy
- /*
* Here saving a last minute SP to current->token acts as a marker:* if we got here, we are successfully faking a sigreturn; in other* words we are sure no bad fatal signal has been raised till now* for unrelated reasons, so we should consider the possibl observedtypo: possible (or possibly?)
possibly
* fatal signal like SEGV coming from Kernel restore_sigframe() and* triggered as expected from our test-case.* For simplicity this assumes that current field 'token' is laid out* as first in struct tdescr*/- ldr x0, current
- str x23, [x0]
- /* SP is already pointing back to the just built fake sigframe here */
- mov x8, #__NR_rt_sigreturn
- svc #0
- /*
* Above sigreturn should not return...looping here leads to a timeout* and ensure proper and clean test failure, instead of jumping around* on a potentially corrupted stack.*/- b .
diff --git a/tools/testing/selftests/arm64/signal/test_signals_utils.h b/tools/testing/selftests/arm64/signal/test_signals_utils.h index ce35be8ebc8e..2a71da7e6695 100644 --- a/tools/testing/selftests/arm64/signal/test_signals_utils.h +++ b/tools/testing/selftests/arm64/signal/test_signals_utils.h @@ -12,4 +12,5 @@ int test_run(struct tdescr *td); void test_result(struct tdescr *td); bool get_current_context(struct tdescr *td, ucontext_t *dest_uc); +int fake_sigreturn(void *sigframe, size_t sz, int alignment); #endif diff --git a/tools/testing/selftests/arm64/signal/testcases/.gitignore b/tools/testing/selftests/arm64/signal/testcases/.gitignore index a48a118b1a1a..0ea6fdc3765c 100644 --- a/tools/testing/selftests/arm64/signal/testcases/.gitignore +++ b/tools/testing/selftests/arm64/signal/testcases/.gitignore @@ -4,3 +4,4 @@ mangle_pstate_invalid_mode_el1 mangle_pstate_invalid_mode_el2 mangle_pstate_invalid_mode_el3 mangle_pstate_ssbs_regs +fake_sigreturn_bad_magic diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c new file mode 100644 index 000000000000..b4c063e02a7a --- /dev/null +++ b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c @@ -0,0 +1,63 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* Copyright (C) 2019 ARM Limited */
We should probably also include <signal.h> here, since we're using siginfo_t etc.
Yes indeed. It was included via some other headers only.
+#include <stdio.h> +#include <ucontext.h>
+#include "test_signals_utils.h" +#include "testcases.h"
+struct fake_sigframe sf;
+static int fake_sigreturn_bad_magic_run(struct tdescr *td,
siginfo_t *si, ucontext_t *uc)+{
- size_t resv_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 2*HDR_SZ space ... one for the KSFT_BAD_MAGIC* and the other for the usual terminator.*/- if (head && resv_sz - offset < HDR_SZ * 2) {
Can we factor out this logic for finding space in the signal frame?
We do pretty much the same thing in all the fake_sigreturn tests...
Ok
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 */
Do we actually time out? I don't see where we actually wait, so doesn't test_run() just fail immediately?
The same applies to all the other fake_sigreturn tests too.
Right. It is probably a leftover.
SIGALRM is used as an extreme measure to kill tests gone bad, but this can happen only once the fake sigframe has been effectively placed on the stack and sigreturned.
- if (head && resv_sz - offset >= HDR_SZ) {
Should this be HDR_SZ * 2 again? We need space for the face header and space to write a terminator after it.
I'll fix in the new factored out code.
fprintf(stderr, "Mangling template header. Spare space:%zd\n",resv_sz - offset);/** use a well known NON existent bad magic...something* we should pretty sure won't be ever defined in Kernel*/head->magic = KSFT_BAD_MAGIC;head->size = HDR_SZ;write_terminator_record(GET_RESV_NEXT_HEAD(head));ASSERT_BAD_CONTEXT(&sf.uc);fake_sigreturn(&sf, sizeof(sf), 16);- }
- return 1;
+}
[...]
Cheers ---Dave
Cheers
Cristian