Re: UBSAN: array-index-out-of-bounds in arch/powerpc/kernel/legacy_serial.c:359:56
From: Christophe Leroy <hidden>
Date: 2021-05-07 08:32:14
Hi Paul, Le 06/05/2021 à 21:32, Paul Menzel a écrit :
[corrected subject] Am 06.05.21 um 21:31 schrieb Paul Menzel:quoted
Dear Linux folks, On the POWER8 system IBM S822LC, Linux 5.13+, built with USSAN, logs the warning below.[ 0.030091] ================================================================================ [ 0.030295] UBSAN: array-index-out-of-bounds in arch/powerpc/kernel/legacy_serial.c:359:56 [ 0.030325] index -1 is out of range for type 'legacy_serial_info [8]' [ 0.030350] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.12.0+ #2 [ 0.030360] Call Trace: [ 0.030363] [c000000024f1bad0] [c0000000009f4330] dump_stack+0xc4/0x114 (unreliable) [ 0.030386] [c000000024f1bb20] [c0000000009efed0] ubsan_epilogue+0x18/0x78 [ 0.030400] [c000000024f1bb80] [c0000000009efafc] __ubsan_handle_out_of_bounds+0xac/0xd0 [ 0.030414] [c000000024f1bc20] [c000000001711588] ioremap_legacy_serial_console+0x54/0x144 [ 0.030430] [c000000024f1bc70] [c0000000000123c0] do_one_initcall+0x60/0x2c0 [ 0.030444] [c000000024f1bd40] [c000000001704bc4] kernel_init_freeable+0x19c/0x25c [ 0.030458] [c000000024f1bda0] [c000000000012a2c] kernel_init+0x2c/0x180 [ 0.030471] [c000000024f1be10] [c00000000000d6ec] ret_from_kernel_thread+0x5c/0x70 [ 0.030484] ================================================================================ [ 0.030641] ================================================================================ [ 0.030668] UBSAN: array-index-out-of-bounds in arch/powerpc/kernel/legacy_serial.c:360:58 [ 0.030697] index -1 is out of range for type 'plat_serial8250_port [9]' [ 0.030721] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.12.0+ #2 [ 0.030730] Call Trace: [ 0.030733] [c000000024f1bad0] [c0000000009f4330] dump_stack+0xc4/0x114 (unreliable) [ 0.030749] [c000000024f1bb20] [c0000000009efed0] ubsan_epilogue+0x18/0x78 [ 0.030762] [c000000024f1bb80] [c0000000009efafc] __ubsan_handle_out_of_bounds+0xac/0xd0 [ 0.030775] [c000000024f1bc20] [c0000000017115a0] ioremap_legacy_serial_console+0x6c/0x144 [ 0.030790] [c000000024f1bc70] [c0000000000123c0] do_one_initcall+0x60/0x2c0 [ 0.030802] [c000000024f1bd40] [c000000001704bc4] kernel_init_freeable+0x19c/0x25c [ 0.030816] [c000000024f1bda0] [c000000000012a2c] kernel_init+0x2c/0x180 [ 0.030829] [c000000024f1be10] [c00000000000d6ec] ret_from_kernel_thread+0x5c/0x70 [ 0.030842] ================================================================================ ```
The function is as follows, so when legacy_serial_console == -1 as in your situation, the pointers
are just not used.
static int __init ioremap_legacy_serial_console(void)
{
struct legacy_serial_info *info = &legacy_serial_infos[legacy_serial_console];
struct plat_serial8250_port *port = &legacy_serial_ports[legacy_serial_console];
void __iomem *vaddr;
if (legacy_serial_console < 0)
return 0;
...
}
When I look into the generated code (UBSAN not selected), we see the verification and the bail-out
is done prior to any calculation based on legacy_serial_console.
00000000 <ioremap_legacy_serial_console>:
0: 94 21 ff e0 stwu r1,-32(r1)
4: 3d 20 00 00 lis r9,0
6: R_PPC_ADDR16_HA .data
8: 7c 08 02 a6 mflr r0
c: bf 81 00 10 stmw r28,16(r1)
10: 3b 80 00 00 li r28,0
14: 83 a9 00 00 lwz r29,0(r9)
16: R_PPC_ADDR16_LO .data
18: 90 01 00 24 stw r0,36(r1)
1c: 2c 1d 00 00 cmpwi r29,0
20: 41 80 00 80 blt a0 <ioremap_legacy_serial_console+0xa0>
So, is it normal that UBSAN reports an error here ?
Thanks
Christophe