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| author | Michael Ellerman <mpe@ellerman.id.au> | 2019-10-16 23:27:32 +1100 |
|---|---|---|
| committer | Christian Brauner <christian.brauner@ubuntu.com> | 2019-10-16 14:56:21 +0200 |
| commit | f418dddffc8007945fd5962380ebde770a240cf5 (patch) | |
| tree | dc19f2a51d74c1bbcde5d1b1b2b7cbbaf47bf1ef /lib/test_user_copy.c | |
| parent | c90012ac85c24547e5c3468ef00aabf44aa7332d (diff) | |
| download | lwn-f418dddffc8007945fd5962380ebde770a240cf5.tar.gz lwn-f418dddffc8007945fd5962380ebde770a240cf5.zip | |
usercopy: Avoid soft lockups in test_check_nonzero_user()
On a machine with a 64K PAGE_SIZE, the nested for loops in
test_check_nonzero_user() can lead to soft lockups, eg:
watchdog: BUG: soft lockup - CPU#4 stuck for 22s! [modprobe:611]
Modules linked in: test_user_copy(+) vmx_crypto gf128mul crc32c_vpmsum virtio_balloon ip_tables x_tables autofs4
CPU: 4 PID: 611 Comm: modprobe Tainted: G L 5.4.0-rc1-gcc-8.2.0-00001-gf5a1a536fa14-dirty #1151
...
NIP __might_sleep+0x20/0xc0
LR __might_fault+0x40/0x60
Call Trace:
check_zeroed_user+0x12c/0x200
test_user_copy_init+0x67c/0x1210 [test_user_copy]
do_one_initcall+0x60/0x340
do_init_module+0x7c/0x2f0
load_module+0x2d94/0x30e0
__do_sys_finit_module+0xc8/0x150
system_call+0x5c/0x68
Even with a 4K PAGE_SIZE the test takes multiple seconds. Instead
tweak it to only scan a 1024 byte region, but make it cross the
page boundary.
Fixes: f5a1a536fa14 ("lib: introduce copy_struct_from_user() helper")
Suggested-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Aleksa Sarai <cyphar@cyphar.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/r/20191016122732.13467-1-mpe@ellerman.id.au
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Diffstat (limited to 'lib/test_user_copy.c')
| -rw-r--r-- | lib/test_user_copy.c | 22 |
1 files changed, 19 insertions, 3 deletions
diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c index ad2372727b1b..5ff04d8fe971 100644 --- a/lib/test_user_copy.c +++ b/lib/test_user_copy.c @@ -47,9 +47,25 @@ static bool is_zeroed(void *from, size_t size) static int test_check_nonzero_user(char *kmem, char __user *umem, size_t size) { int ret = 0; - size_t start, end, i; - size_t zero_start = size / 4; - size_t zero_end = size - zero_start; + size_t start, end, i, zero_start, zero_end; + + if (test(size < 2 * PAGE_SIZE, "buffer too small")) + return -EINVAL; + + /* + * We want to cross a page boundary to exercise the code more + * effectively. We also don't want to make the size we scan too large, + * otherwise the test can take a long time and cause soft lockups. So + * scan a 1024 byte region across the page boundary. + */ + size = 1024; + start = PAGE_SIZE - (size / 2); + + kmem += start; + umem += start; + + zero_start = size / 4; + zero_end = size - zero_start; /* * We conduct a series of check_nonzero_user() tests on a block of |