On Tue, Apr 15, 2025 at 08:33:54PM +0000, Mostafa Saleh wrote:
> 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 <smost...@google.com>
Looks good; thanks!
Reviewed-by: Kees Cook <k...@kernel.org>
--
Kees Cook
