On Mon, Jun 08, 2020 at 02:04:08PM +0800, kernel test robot wrote: > The issue seems due to the lack of "-fsanitize-undefined-trap-on-error" in clang. Hm? No, that's supported in Clang (at least as far back as Clang 9.) > Greetings, > > 0day kernel testing robot got the below dmesg and the first bad commit is > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master > > commit 0887a7ebc97770c7870abf3075a2e8cd502a7f52 > Author: Kees Cook <keescook@xxxxxxxxxxxx> > AuthorDate: Mon Apr 6 20:12:27 2020 -0700 > Commit: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > CommitDate: Tue Apr 7 10:43:44 2020 -0700 > > ubsan: add trap instrumentation option In the randconfig, I see CONFIG_UBSAN_TRAP is enabled with lots of other UBSAN options. If you're not expecting the results, it's very likely the false positives in UBSAN are going to do bad things. :) This is "working as expected", as noted in the commit log quoted below. > > Patch series "ubsan: Split out bounds checker", v5. > > This splits out the bounds checker so it can be individually used. This > is enabled in Android and hopefully for syzbot. Includes LKDTM tests for > behavioral corner-cases (beyond just the bounds checker), and adjusts > ubsan and kasan slightly for correct panic handling. > > This patch (of 6): > > The Undefined Behavior Sanitizer can operate in two modes: warning > reporting mode via lib/ubsan.c handler calls, or trap mode, which uses > __builtin_trap() as the handler. Using lib/ubsan.c means the kernel image > is about 5% larger (due to all the debugging text and reporting structures > to capture details about the warning conditions). Using the trap mode, > the image size changes are much smaller, though at the loss of the > "warning only" mode. > > In order to give greater flexibility to system builders that want minimal > changes to image size and are prepared to deal with kernel code being > aborted and potentially destabilizing the system, this introduces > CONFIG_UBSAN_TRAP. The resulting image sizes comparison: > > text data bss dec hex filename > 19533663 6183037 18554956 44271656 2a38828 vmlinux.stock > 19991849 7618513 18874448 46484810 2c54d4a vmlinux.ubsan > 19712181 6284181 18366540 44362902 2a4ec96 vmlinux.ubsan-trap > > CONFIG_UBSAN=y: image +4.8% (text +2.3%, data +18.9%) > CONFIG_UBSAN_TRAP=y: image +0.2% (text +0.9%, data +1.6%) > > Additionally adjusts the CONFIG_UBSAN Kconfig help for clarity and removes > the mention of non-existing boot param "ubsan_handle". If you're trying to _boot_ a randconfig, I suspect there are going to be a lot of surprises with UBSAN (in any mode) enabled. Right now, likely the least noisy of them all is UBSAN_BOUNDS, which was split out for fuzzers. FWIW, the dmesg appears to be catching a NULL pointer dereference (enabled via CONFIG_UBSAN_MISC): [ 0.047646] UBSAN: Undefined behaviour in drivers/acpi/acpica/tbfadt.c:459:37 [ 0.047650] member access within null pointer of type 'struct acpi_table_fadt' [ 0.047655] CPU: 0 PID: 0 Comm: swapper Not tainted 5.6.0-11597-g7baf219982281 #1 [ 0.047659] Call Trace: [ 0.047676] dump_stack+0x88/0xb9 [ 0.047684] ? ubsan_prologue+0x21/0x46 [ 0.047689] ? ubsan_type_mismatch_common+0x188/0x19e [ 0.047695] ? __ubsan_handle_type_mismatch_v1+0x45/0x4a [ 0.047701] ? acpi_tb_create_local_fadt+0xaa/0x435 [ 0.047706] ? acpi_tb_parse_fadt+0x54/0xd4 [ 0.047712] ? acpi_tb_parse_root_table+0x192/0x1bf [ 0.047717] ? acpi_table_init+0x3b/0x56 [ 0.047721] ? acpi_boot_table_init+0xf/0x6e [ 0.047726] ? setup_arch+0x459/0x520 [ 0.047732] ? start_kernel+0x5e/0x3ba [ 0.047737] ? secondary_startup_64+0xa4/0xb0 I'm not sure how ACPI defines acpi_gbl_FADT though? There's no dereference... 459: if (acpi_gbl_FADT.header.length <= ACPI_FADT_V2_SIZE) { BTW, this report only contained 1 actual dmesg. There were two files with dmesg file names, but one of them was the gzipped reproduction steps again. -Kees -- Kees Cook
