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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Thu, 7 May 2020 11:30:34 -0700
Message-ID: <CAKwvOdmMjwoTZFSp2DnzeKePxgczfOJyOH_T-vyzHGcm5cFXgA@mail.gmail.com>
Subject: Re: Clang and UBSAN: member access within null pointer of type
To:     Qian Cai <cai@lca.pw>
Cc:     Nathan Chancellor <natechancellor@gmail.com>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Will Deacon <will@kernel.org>
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On Thu, May 7, 2020 at 6:42 AM Qian Cai <cai@lca.pw> wrote:
>
> Running a Clang (9.0.1) build kernel with UBSAN generated a few warnings during boot,

Very cool, these reports are so nice! They hand you everything on a
silver platter.  Thanks for testing/sending!  Let's take a look.

>
> [    0.000000] UBSAN: null-ptr-deref in drivers/acpi/acpica/tbfadt.c:459:37
> [    0.000000] member access within null pointer of type 'struct acpi_table_fadt'
> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.7.0-rc4-next-20200507 #2
> [    0.000000] Call trace:
> [    0.000000]  dump_backtrace+0x0/0x22c
> [    0.000000]  show_stack+0x28/0x34
> [    0.000000]  dump_stack+0x104/0x194
> [    0.000000]  handle_null_ptr_deref+0xdc/0x10c
> [    0.000000]  __ubsan_handle_type_mismatch_v1+0x64/0x78
> [    0.000000]  acpi_tb_create_local_fadt+0x104/0x6ec

ok so acpi_tb_create_local_fadt() dereferenced a `null pointer of type
'struct acpi_table_fadt'` in null-ptr-deref in
drivers/acpi/acpica/tbfadt.c:459.

That line number doesn't line up with linux-next; which tree was this?
 That will probably help track these down faster.

> [    0.000000]  acpi_tb_parse_fadt+0xa0/0x1a0
> [    0.000000]  acpi_tb_parse_root_table+0x284/0x2ac
> [    0.000000]  acpi_initialize_tables+0xb4/0xd0
> [    0.000000]  acpi_table_init+0x68/0x88
> [    0.000000]  acpi_boot_table_init+0x108/0x1a0
> [    0.000000]  setup_arch+0xec/0x1f4
> [    0.000000]  start_kernel+0x94/0x56c
>
> [    0.000000] UBSAN: null-ptr-deref in arch/arm64/kernel/smp.c:596:6
> [    0.000000] member access within null pointer of type 'struct acpi_madt_generic_interrupt'
> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.7.0-rc4-next-20200507 #2
> [    0.000000] Call trace:
> [    0.000000]  dump_backtrace+0x0/0x22c
> [    0.000000]  show_stack+0x28/0x34
> [    0.000000]  dump_stack+0x104/0x194
> [    0.000000]  handle_null_ptr_deref+0xdc/0x10c
> [    0.000000]  __ubsan_handle_type_mismatch_v1+0x64/0x78
> [    0.000000]  acpi_parse_gic_cpu_interface+0x40/0xa8
> [    0.000000]  acpi_parse_entries_array+0x1d4/0x2e8
> [    0.000000]  acpi_table_parse_entries_array+0x11c/0x138
> [    0.000000]  acpi_table_parse_madt+0x84/0xb0
> [    0.000000]  acpi_parse_and_init_cpus+0x24/0x80
> [    0.000000]  smp_init_cpus+0x38/0x17c
> [    0.000000]  setup_arch+0x140/0x1f4
> [    0.000000]  start_kernel+0x94/0x56c
>
> [  255.388250] UBSAN: null-ptr-deref in ./fs/xfs/xfs_sysfs.h:37:23
> [  255.394898] member access within null pointer of type 'struct xfs_kobj'
> [  255.402346] CPU: 230 PID: 2364 Comm: modprobe Tainted: G             L    5.7.0-rc4-next-20200507 #2
> [  255.412191] Hardware name: HPE Apollo 70             /C01_APACHE_MB         , BIOS L50_5.13_1.11 06/18/2019
> [  255.422641] Call trace:
> [  255.425811]  dump_backtrace+0x0/0x22c
> [  255.430188]  show_stack+0x28/0x34
> [  255.434225]  dump_stack+0x104/0x194
> [  255.438441]  handle_null_ptr_deref+0xdc/0x10c
> [  255.443511]  __ubsan_handle_type_mismatch_v1+0x64/0x78
> [  255.450016]  init_module+0x130/0x1d4 [xfs]
> [  255.454831]  do_one_initcall+0x6c/0x144
> [  255.459383]  do_init_module+0x100/0x388
> [  255.463931]  load_module+0x2518/0x2b9c
> [  255.468404]  __se_sys_finit_module+0x144/0x150
> [  255.473560]  __arm64_sys_finit_module+0x54/0x88
> [  255.478804]  do_el0_svc+0x128/0x1dc
> [  255.483010]  el0_sync_handler+0xd0/0x268
> [  255.487655]  el0_sync+0x164/0x180
> [  255.491782] ================================================================================
> [  255.769799] ================================================================================
> [  255.779164] UBSAN: null-ptr-deref in ./fs/xfs/xfs_sysfs.h:37:23
> [  255.785816] member access within null pointer of type 'struct xfs_kobj'
> [  255.793268] CPU: 132 PID: 2363 Comm: mount Tainted: G             L    5.7.0-rc4-next-20200507 #2
> [  255.802854] Hardware name: HPE Apollo 70             /C01_APACHE_MB         , BIOS L50_5.13_1.11 06/18/2019
> [  255.813306] Call trace:
> [  255.816471]  dump_backtrace+0x0/0x22c
> [  255.820849]  show_stack+0x28/0x34
> [  255.824882]  dump_stack+0x104/0x194
> [  255.829090]  handle_null_ptr_deref+0xdc/0x10c
> [  255.834163]  __ubsan_handle_type_mismatch_v1+0x64/0x78
> [  255.840665]  xfs_mountfs+0x310/0xc64 [xfs]
> [  255.846071]  xfs_fc_fill_super+0x5cc/0x75c [xfs]
> [  255.851411]  get_tree_bdev+0x24c/0x328
> [  255.856463]  xfs_fc_get_tree+0x24/0x30 [xfs]
> [  255.861453]  vfs_get_tree+0x54/0x158
> [  255.865754]  do_mount+0x80c/0xaf0
> [  255.869786]  __arm64_sys_mount+0xe0/0x18c
> [  255.874510]  do_el0_svc+0x128/0x1dc
> [  255.878720]  el0_sync_handler+0xd0/0x268
> [  255.883357]  el0_sync+0x164/0x180


-- 
Thanks,
~Nick Desaulniers