On 11/07/2017 12:39 PM, Fengguang Wu wrote: > Hello, > > FYI this happens in v4.14-rc8 -- it's not necessarily a new bug. > > [ 22.184920] Freeing unused kernel memory: 824K > [ 22.199198] Freeing unused kernel memory: 1436K > [ 22.228460] x86/mm: Checked W+X mappings: passed, no W+X pages found. > [ 22.230474] rodata_test: all tests were successful > [ 22.254830] > ================================================================== > [ 22.257125] BUG: KASAN: slab-out-of-bounds in copyin+0xea/0x170 > [ 22.258648] Write of size 26 at addr ffff880013432540 by task init/1 > [ 22.260272]
It says that we write 26 bytes starting from ffff880013432540. But according to the dump of shadow memory: [ 22.297667] >ffff880013432500: fc fc fb fb fb fb fc fc 00 00 00 03 fc fc fb fb [ 22.298581] ^ we have allocated 27 bytes at address stating from ffff880013432540. So this looks like a false positive. I've seen reports like this before: https://lkml.kernel.org/r/<[email protected]> https://lkml.kernel.org/r/<[email protected]> This happens only on old gcc versions, in your case it's 4.6: [ 0.000000] Linux version 4.14.0-rc8 (kbuild@lkp-wsx01) (gcc version 4.6.4 (Debian 4.6.4-7)) #14 SMP PREEMPT Tue Nov 7 06:50:21 CST 2017 Old GCC is misscompiling something in check_memory_region() which cause false-positive like this one. I never bothered to dig it deeper, because I've never seen this with GCC versions (>= 4.9.2) that actually support KASAN. It's almost pointless to use KASAN=y kernel built with old GCC. All memory accesses, except manually instrumented with kasan_check_[read|write](), won't be checked.
