From: Mostafa Saleh smostafa@google.com
[ Upstream commit 9b044614be12d78d3a93767708b8d02fb7dfa9b0 ]
Running lib_ubsan.ko on arm64 (without CONFIG_UBSAN_TRAP) panics the kernel:
[ 31.616546] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: test_ubsan_out_of_bounds+0x158/0x158 [test_ubsan] [ 31.646817] CPU: 3 UID: 0 PID: 179 Comm: insmod Not tainted 6.15.0-rc2 #1 PREEMPT [ 31.648153] Hardware name: linux,dummy-virt (DT) [ 31.648970] Call trace: [ 31.649345] show_stack+0x18/0x24 (C) [ 31.650960] dump_stack_lvl+0x40/0x84 [ 31.651559] dump_stack+0x18/0x24 [ 31.652264] panic+0x138/0x3b4 [ 31.652812] __ktime_get_real_seconds+0x0/0x10 [ 31.653540] test_ubsan_load_invalid_value+0x0/0xa8 [test_ubsan] [ 31.654388] init_module+0x24/0xff4 [test_ubsan] [ 31.655077] do_one_initcall+0xd4/0x280 [ 31.655680] do_init_module+0x58/0x2b4
That happens because the test corrupts other data in the stack: 400: d5384108 mrs x8, sp_el0 404: f9426d08 ldr x8, [x8, #1240] 408: f85f83a9 ldur x9, [x29, #-8] 40c: eb09011f cmp x8, x9 410: 54000301 b.ne 470 <test_ubsan_out_of_bounds+0x154> // b.any
As there is no guarantee the compiler will order the local variables as declared in the module: volatile char above[4] = { }; /* Protect surrounding memory. */ volatile int arr[4]; volatile char below[4] = { }; /* Protect surrounding memory. */
There is another problem where the out-of-bound index is 5 which is larger than the extra surrounding memory for protection.
So, use a struct to enforce the ordering, and fix the index to be 4. Also, remove some of the volatiles and rely on OPTIMIZER_HIDE_VAR()
Signed-off-by: Mostafa Saleh smostafa@google.com Link: https://lore.kernel.org/r/20250415203354.4109415-1-smostafa@google.com Signed-off-by: Kees Cook kees@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- lib/test_ubsan.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-)
diff --git a/lib/test_ubsan.c b/lib/test_ubsan.c index 2062be1f2e80f..f90f2b9842ec4 100644 --- a/lib/test_ubsan.c +++ b/lib/test_ubsan.c @@ -35,18 +35,22 @@ static void test_ubsan_shift_out_of_bounds(void)
static void test_ubsan_out_of_bounds(void) { - volatile int i = 4, j = 5, k = -1; - volatile char above[4] = { }; /* Protect surrounding memory. */ - volatile int arr[4]; - volatile char below[4] = { }; /* Protect surrounding memory. */ + int i = 4, j = 4, k = -1; + volatile struct { + char above[4]; /* Protect surrounding memory. */ + int arr[4]; + char below[4]; /* Protect surrounding memory. */ + } data;
- above[0] = below[0]; + OPTIMIZER_HIDE_VAR(i); + OPTIMIZER_HIDE_VAR(j); + OPTIMIZER_HIDE_VAR(k);
UBSAN_TEST(CONFIG_UBSAN_BOUNDS, "above"); - arr[j] = i; + data.arr[j] = i;
UBSAN_TEST(CONFIG_UBSAN_BOUNDS, "below"); - arr[k] = i; + data.arr[k] = i; }
enum ubsan_test_enum {