Messages in this thread |  | | From | Dmitry Vyukov <> | Date | Tue, 30 Jan 2018 10:23:42 +0100 | Subject | Re: [PATCH v6 0/4] x86, kasan: add KASAN checks to atomic operations |
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On Mon, Jan 29, 2018 at 6:26 PM, Dmitry Vyukov <dvyukov@google.com> wrote: > KASAN uses compiler instrumentation to intercept all memory accesses. > But it does not see memory accesses done in assembly code. > One notable user of assembly code is atomic operations. Frequently, > for example, an atomic reference decrement is the last access to an > object and a good candidate for a racy use-after-free. > > Atomic operations are defined in arch files, but KASAN instrumentation > is required for several archs that support KASAN. Later we will need > similar hooks for KMSAN (uninit use detector) and KTSAN (data race > detector). > > This change introduces wrappers around atomic operations that can be > used to add KASAN/KMSAN/KTSAN instrumentation across several archs, > and adds KASAN checks to them. > > This patch uses the wrappers only for x86 arch. Arm64 will be switched > later. And we also plan to instrument bitops in a similar way. > > Within a day it has found its first bug: > > BUG: KASAN: use-after-free in atomic_dec_and_test > arch/x86/include/asm/atomic.h:123 [inline] at addr ffff880079c30158 > Write of size 4 by task syz-executor6/25698 > CPU: 2 PID: 25698 Comm: syz-executor6 Not tainted 4.10.0+ #302 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > Call Trace: > kasan_check_write+0x14/0x20 mm/kasan/kasan.c:344 > atomic_dec_and_test arch/x86/include/asm/atomic.h:123 [inline] > put_task_struct include/linux/sched/task.h:93 [inline] > put_ctx+0xcf/0x110 kernel/events/core.c:1131 > perf_event_release_kernel+0x3ad/0xc90 kernel/events/core.c:4322 > perf_release+0x37/0x50 kernel/events/core.c:4338 > __fput+0x332/0x800 fs/file_table.c:209 > ____fput+0x15/0x20 fs/file_table.c:245 > task_work_run+0x197/0x260 kernel/task_work.c:116 > exit_task_work include/linux/task_work.h:21 [inline] > do_exit+0xb38/0x29c0 kernel/exit.c:880 > do_group_exit+0x149/0x420 kernel/exit.c:984 > get_signal+0x7e0/0x1820 kernel/signal.c:2318 > do_signal+0xd2/0x2190 arch/x86/kernel/signal.c:808 > exit_to_usermode_loop+0x200/0x2a0 arch/x86/entry/common.c:157 > syscall_return_slowpath arch/x86/entry/common.c:191 [inline] > do_syscall_64+0x6fc/0x930 arch/x86/entry/common.c:286 > entry_SYSCALL64_slow_path+0x25/0x25 > RIP: 0033:0x4458d9 > RSP: 002b:00007f3f07187cf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca > RAX: fffffffffffffe00 RBX: 00000000007080c8 RCX: 00000000004458d9 > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000007080c8 > RBP: 00000000007080a8 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > R13: 0000000000000000 R14: 00007f3f071889c0 R15: 00007f3f07188700 > Object at ffff880079c30140, in cache task_struct size: 5376 > Allocated: > PID = 25681 > kmem_cache_alloc_node+0x122/0x6f0 mm/slab.c:3662 > alloc_task_struct_node kernel/fork.c:153 [inline] > dup_task_struct kernel/fork.c:495 [inline] > copy_process.part.38+0x19c8/0x4aa0 kernel/fork.c:1560 > copy_process kernel/fork.c:1531 [inline] > _do_fork+0x200/0x1010 kernel/fork.c:1994 > SYSC_clone kernel/fork.c:2104 [inline] > SyS_clone+0x37/0x50 kernel/fork.c:2098 > do_syscall_64+0x2e8/0x930 arch/x86/entry/common.c:281 > return_from_SYSCALL_64+0x0/0x7a > Freed: > PID = 25681 > __cache_free mm/slab.c:3514 [inline] > kmem_cache_free+0x71/0x240 mm/slab.c:3774 > free_task_struct kernel/fork.c:158 [inline] > free_task+0x151/0x1d0 kernel/fork.c:370 > copy_process.part.38+0x18e5/0x4aa0 kernel/fork.c:1931 > copy_process kernel/fork.c:1531 [inline] > _do_fork+0x200/0x1010 kernel/fork.c:1994 > SYSC_clone kernel/fork.c:2104 [inline] > SyS_clone+0x37/0x50 kernel/fork.c:2098 > do_syscall_64+0x2e8/0x930 arch/x86/entry/common.c:281 > return_from_SYSCALL_64+0x0/0x7a > > Changes since v1: > - dropped "x86: remove unused atomic_inc_short()" patch > it is mailed separately > - rebased on top of tip/locking/core head > - other changes noted within individual patches > > Changes since v2: > - rebased on top of tip/locking/core head > - dropped a pervasive "x86: use long long for 64-bit atomic ops" commit, > instead use s64 type in wrappers > - added "x86: use s64* for old arg of atomic64_try_cmpxchg()" commit > > Changes since v3 are noted in individual commits. > > Changes since v4: > - rebased on tip/locking/core HEAD > > Changes since v5: > - rework cmpxchg* implementations so that we have less > code in macros and more code in functions
Some context. This revives a half-year old patch. v5 of this was applied to tip/locking/core, but then reverted due to a reported crash: https://groups.google.com/d/msg/kasan-dev/ZJl66N7smmk/lJY99HmmAgAJ
The root cause was in the cmpxchg macros:
#define cmpxchg64(ptr, old, new) \ ({ \ __typeof__(ptr) ____ptr = (ptr); \ kasan_check_write(____ptr, sizeof(*____ptr)); \ arch_cmpxchg64(____ptr, (old), (new)); \ })
I had to introduce the new ____ptr variable, so that kasan_check_write() and arch_cmpxchg64() don't evaluate ptr twice. But there are multiple layers of macros and ____ptr ended up referring to something else (to itself).
v6 changes cmpxchg macros to (as was suggested by Mark and Thomas):
static __always_inline unsigned long cmpxchg_size(volatile void *ptr, unsigned long old, unsigned long new, int size) { kasan_check_write(ptr, size); switch (size) { case 1: return arch_cmpxchg((u8 *)ptr, (u8)old, (u8)new); case 2: return arch_cmpxchg((u16 *)ptr, (u16)old, (u16)new); case 4: return arch_cmpxchg((u32 *)ptr, (u32)old, (u32)new); case 8: BUILD_BUG_ON(sizeof(unsigned long) != 8); return arch_cmpxchg((u64 *)ptr, (u64)old, (u64)new); } BUILD_BUG(); return 0; }
#define cmpxchg(ptr, old, new) \ ({ \ ((__typeof__(*(ptr)))cmpxchg_size((ptr), (unsigned long)(old), \ (unsigned long)(new), sizeof(*(ptr)))); \ })
Otherwise the patch series were rebased without any conflicts (surprisingly).
There is now some duplication between cmpxchg_size, cmpxchg_local_size and sync_cmpxchg_size, but I thought that employing more macros while trying to resolve macro mess bugs is not the best idea.
> Tested: > - build/boot x86_64 defconfig > - build/boot x86_64 defconfig+KASAN > - build i686/powerpc defconfig > > Dmitry Vyukov (4): > locking/atomic: Add asm-generic/atomic-instrumented.h > x86: switch atomic.h to use atomic-instrumented.h > asm-generic: add KASAN instrumentation to atomic operations > asm-generic, x86: add comments for atomic instrumentation > > arch/x86/include/asm/atomic.h | 106 +++---- > arch/x86/include/asm/atomic64_32.h | 106 +++---- > arch/x86/include/asm/atomic64_64.h | 108 +++---- > arch/x86/include/asm/cmpxchg.h | 12 +- > arch/x86/include/asm/cmpxchg_32.h | 8 +- > arch/x86/include/asm/cmpxchg_64.h | 4 +- > include/asm-generic/atomic-instrumented.h | 476 ++++++++++++++++++++++++++++++ > 7 files changed, 652 insertions(+), 168 deletions(-) > create mode 100644 include/asm-generic/atomic-instrumented.h > > -- > 2.16.0.rc1.238.g530d649a79-goog >
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