The patch titled Subject: lib/test_ubsan.c: fix panic from test_ubsan_out_of_bounds has been added to the -mm mm-hotfixes-unstable branch. Its filename is lib-test_ubsanc-fix-panic-from-test_ubsan_out_of_bounds.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Mostafa Saleh smostafa@google.com Subject: lib/test_ubsan.c: fix panic from test_ubsan_out_of_bounds Date: Mon, 14 Apr 2025 21:36:48 +0000

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. */

So, instead of writing out-of-bound, we can read out-of-bound which still triggers UBSAN but doesn't corrupt the stack.

Link: https://lkml.kernel.org/r/20250414213648.2660150-1-smostafa@google.com Fixes: 4a26f49b7b3d ubsan: ("expand tests and reporting") Signed-off-by: Mostafa Saleh smostafa@google.com Cc: Andrey Konovalov andreyknvl@gmail.com Cc: Andrey Ryabinin ryabinin.a.a@gmail.com Cc: Macro Elver elver@google.com Cc: Kees Cook kees@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

lib/test_ubsan.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-)

--- a/lib/test_ubsan.c~lib-test_ubsanc-fix-panic-from-test_ubsan_out_of_bounds +++ a/lib/test_ubsan.c @@ -77,18 +77,15 @@ static void test_ubsan_shift_out_of_boun

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 j = 5, k = -1; + volatile int scratch[4] = { }; volatile int arr[4]; - volatile char below[4] = { }; /* Protect surrounding memory. */ - - above[0] = below[0];

UBSAN_TEST(CONFIG_UBSAN_BOUNDS, "above"); - arr[j] = i; + scratch[1] = arr[j];

UBSAN_TEST(CONFIG_UBSAN_BOUNDS, "below"); - arr[k] = i; + scratch[2] = arr[k]; }

enum ubsan_test_enum { _

Patches currently in -mm which might be from smostafa@google.com are

lib-test_ubsanc-fix-panic-from-test_ubsan_out_of_bounds.patch