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selftests/bpf: fexit_sleep: Fix stack allocation for arm64

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On ARM64 the stack pointer should be aligned at a 16 byte boundary or
the SPAlignmentFault can occur. The fexit_sleep selftest allocates the
stack for the child process as a character array, this is not guaranteed
to be aligned at 16 bytes.

Because of the SPAlignmentFault, the child process is killed before it
can do the nanosleep call and hence fentry_cnt remains as 0. This causes
the main thread to hang on the following line:

while (READ_ONCE(fexit_skel->bss->fentry_cnt) != 2);

Fix this by allocating the stack using mmap() as described in the
example in the man page of clone().

Remove the fexit_sleep test from the DENYLIST of arm64.

Fixes: eddbe8e652 ("selftest/bpf: Add a test to check trampoline freeing logic.")
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240715173327.8657-1-puranjay@kernel.org
This commit is contained in:
Puranjay Mohan 2024-07-15 17:33:27 +00:00 committed by Daniel Borkmann
parent 0e03c643dc
commit e1ef78dce9
2 changed files with 7 additions and 2 deletions
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1
tools/testing/selftests/bpf/DENYLIST.aarch64
View file

@ -1,6 +1,5 @@
bpf_cookie/multi_kprobe_attach_api # kprobe_multi_link_api_subtest:FAIL:fentry_raw_skel_load unexpected error: -3
bpf_cookie/multi_kprobe_link_api # kprobe_multi_link_api_subtest:FAIL:fentry_raw_skel_load unexpected error: -3
fexit_sleep # The test never returns. The remaining tests cannot start.
kprobe_multi_bench_attach # needs CONFIG_FPROBE
kprobe_multi_test # needs CONFIG_FPROBE
module_attach # prog 'kprobe_multi': failed to auto-attach: -95

8
tools/testing/selftests/bpf/prog_tests/fexit_sleep.c
View file

@ -21,13 +21,13 @@ static int do_sleep(void *skel)
}
#define STACK_SIZE (1024 * 1024)
static char child_stack[STACK_SIZE];
void test_fexit_sleep(void)
{
struct fexit_sleep_lskel *fexit_skel = NULL;
int wstatus, duration = 0;
pid_t cpid;
char *child_stack = NULL;
int err, fexit_cnt;
fexit_skel = fexit_sleep_lskel__open_and_load();
@ -38,6 +38,11 @@ void test_fexit_sleep(void)
if (CHECK(err, "fexit_attach", "fexit attach failed: %d\n", err))
goto cleanup;
child_stack = mmap(NULL, STACK_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE |
MAP_ANONYMOUS | MAP_STACK, -1, 0);
if (!ASSERT_NEQ(child_stack, MAP_FAILED, "mmap"))
goto cleanup;
cpid = clone(do_sleep, child_stack + STACK_SIZE, CLONE_FILES | SIGCHLD, fexit_skel);
if (CHECK(cpid == -1, "clone", "%s\n", strerror(errno)))
goto cleanup;
@ -78,5 +83,6 @@ void test_fexit_sleep(void)
goto cleanup;
cleanup:
munmap(child_stack, STACK_SIZE);
fexit_sleep_lskel__destroy(fexit_skel);
}