Patch "selftests/bpf: fexit_sleep: Fix stack allocation for arm64" has been added to the 6.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    selftests/bpf: fexit_sleep: Fix stack allocation for arm64

to the 6.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     selftests-bpf-fexit_sleep-fix-stack-allocation-for-a.patch
and it can be found in the queue-6.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit f21d2b558227539ba0cc577345a251918793e6cc
Author: Puranjay Mohan <puranjay@xxxxxxxxxx>
Date:   Mon Jul 15 17:33:27 2024 +0000

    selftests/bpf: fexit_sleep: Fix stack allocation for arm64
    
    [ Upstream commit e1ef78dce9b7b0fa7f9d88bb3554441d74d33b34 ]
    
    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: eddbe8e65214 ("selftest/bpf: Add a test to check trampoline freeing logic.")
    Signed-off-by: Puranjay Mohan <puranjay@xxxxxxxxxx>
    Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
    Link: https://lore.kernel.org/bpf/20240715173327.8657-1-puranjay@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/tools/testing/selftests/bpf/DENYLIST.aarch64 b/tools/testing/selftests/bpf/DENYLIST.aarch64
index 0445ac38bc07d..3a2261248e9af 100644
--- a/tools/testing/selftests/bpf/DENYLIST.aarch64
+++ b/tools/testing/selftests/bpf/DENYLIST.aarch64
@@ -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
diff --git a/tools/testing/selftests/bpf/prog_tests/fexit_sleep.c b/tools/testing/selftests/bpf/prog_tests/fexit_sleep.c
index f949647dbbc21..552a0875ca6db 100644
--- a/tools/testing/selftests/bpf/prog_tests/fexit_sleep.c
+++ b/tools/testing/selftests/bpf/prog_tests/fexit_sleep.c
@@ -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);
 }