Re: UBSAN: array-index-out-of-bounds in arch/powerpc/kernel/legacy_serial.c:359:56

[+Andrey]

Dear Christophe,


Am 07.05.21 um 10:31 schrieb Christophe Leroy:

Le 06/05/2021 à 21:32, Paul Menzel a écrit :

quoted

[corrected subject]

Am 06.05.21 um 21:31 schrieb Paul Menzel:

quoted

quoted

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 ?

If it’s useful, I could disassemble the code here. But please tell me how.

Sorry, I do not know. I just selected the option, and saw the error. 
Maybe Andrey has an idea.


Kind regards,

Paul