Messages in this thread | | | Date | Wed, 2 Nov 2022 15:19:52 +0800 | Subject | Re: [PATCH -next] bpf, test_run: fix alignment problem in bpf_prog_test_run_skb() | From | zhongbaisong <> |
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On 2022/11/2 12:37, Eric Dumazet wrote: > On Tue, Nov 1, 2022 at 9:27 PM Kees Cook <keescook@chromium.org> wrote: >> >> On Tue, Nov 01, 2022 at 09:05:42PM -0700, Jakub Kicinski wrote: >>> On Wed, 2 Nov 2022 10:59:44 +0800 zhongbaisong wrote: >>>> On 2022/11/2 0:45, Daniel Borkmann wrote: >>>>> [ +kfence folks ] >>>> >>>> + cc: Alexander Potapenko, Marco Elver, Dmitry Vyukov >>>> >>>> Do you have any suggestions about this problem? >>> >>> + Kees who has been sending similar patches for drivers >>> >>>>> On 11/1/22 5:04 AM, Baisong Zhong wrote: >>>>>> Recently, we got a syzkaller problem because of aarch64 >>>>>> alignment fault if KFENCE enabled. >>>>>> >>>>>> When the size from user bpf program is an odd number, like >>>>>> 399, 407, etc, it will cause skb shard info's alignment access, >>>>>> as seen below: >>>>>> >>>>>> BUG: KFENCE: use-after-free read in __skb_clone+0x23c/0x2a0 >>>>>> net/core/skbuff.c:1032 >>>>>> >>>>>> Use-after-free read at 0xffff6254fffac077 (in kfence-#213): >>>>>> __lse_atomic_add arch/arm64/include/asm/atomic_lse.h:26 [inline] >>>>>> arch_atomic_add arch/arm64/include/asm/atomic.h:28 [inline] >>>>>> arch_atomic_inc include/linux/atomic-arch-fallback.h:270 [inline] >>>>>> atomic_inc include/asm-generic/atomic-instrumented.h:241 [inline] >>>>>> __skb_clone+0x23c/0x2a0 net/core/skbuff.c:1032 >>>>>> skb_clone+0xf4/0x214 net/core/skbuff.c:1481 >>>>>> ____bpf_clone_redirect net/core/filter.c:2433 [inline] >>>>>> bpf_clone_redirect+0x78/0x1c0 net/core/filter.c:2420 >>>>>> bpf_prog_d3839dd9068ceb51+0x80/0x330 >>>>>> bpf_dispatcher_nop_func include/linux/bpf.h:728 [inline] >>>>>> bpf_test_run+0x3c0/0x6c0 net/bpf/test_run.c:53 >>>>>> bpf_prog_test_run_skb+0x638/0xa7c net/bpf/test_run.c:594 >>>>>> bpf_prog_test_run kernel/bpf/syscall.c:3148 [inline] >>>>>> __do_sys_bpf kernel/bpf/syscall.c:4441 [inline] >>>>>> __se_sys_bpf+0xad0/0x1634 kernel/bpf/syscall.c:4381 >>>>>> >>>>>> kfence-#213: 0xffff6254fffac000-0xffff6254fffac196, size=407, >>>>>> cache=kmalloc-512 >>>>>> >>>>>> allocated by task 15074 on cpu 0 at 1342.585390s: >>>>>> kmalloc include/linux/slab.h:568 [inline] >>>>>> kzalloc include/linux/slab.h:675 [inline] >>>>>> bpf_test_init.isra.0+0xac/0x290 net/bpf/test_run.c:191 >>>>>> bpf_prog_test_run_skb+0x11c/0xa7c net/bpf/test_run.c:512 >>>>>> bpf_prog_test_run kernel/bpf/syscall.c:3148 [inline] >>>>>> __do_sys_bpf kernel/bpf/syscall.c:4441 [inline] >>>>>> __se_sys_bpf+0xad0/0x1634 kernel/bpf/syscall.c:4381 >>>>>> __arm64_sys_bpf+0x50/0x60 kernel/bpf/syscall.c:4381 >>>>>> >>>>>> To fix the problem, we round up allocations with kmalloc_size_roundup() >>>>>> so that build_skb()'s use of kize() is always alignment and no special >>>>>> handling of the memory is needed by KFENCE. >>>>>> >>>>>> Fixes: 1cf1cae963c2 ("bpf: introduce BPF_PROG_TEST_RUN command") >>>>>> Signed-off-by: Baisong Zhong <zhongbaisong@huawei.com> >>>>>> --- >>>>>> net/bpf/test_run.c | 1 + >>>>>> 1 file changed, 1 insertion(+) >>>>>> >>>>>> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c >>>>>> index 13d578ce2a09..058b67108873 100644 >>>>>> --- a/net/bpf/test_run.c >>>>>> +++ b/net/bpf/test_run.c >>>>>> @@ -774,6 +774,7 @@ static void *bpf_test_init(const union bpf_attr >>>>>> *kattr, u32 user_size, >>>>>> if (user_size > size) >>>>>> return ERR_PTR(-EMSGSIZE); >>>>>> + size = kmalloc_size_roundup(size); >>>>>> data = kzalloc(size + headroom + tailroom, GFP_USER); >>>>> >>>>> The fact that you need to do this roundup on call sites feels broken, no? >>>>> Was there some discussion / consensus that now all k*alloc() call sites >>>>> would need to be fixed up? Couldn't this be done transparently in k*alloc() >>>>> when KFENCE is enabled? I presume there may be lots of other such occasions >>>>> in the kernel where similar issue triggers, fixing up all call-sites feels >>>>> like ton of churn compared to api-internal, generic fix. >> >> I hope I answer this in more detail here: >> https://lore.kernel.org/lkml/202211010937.4631CB1B0E@keescook/ >> >> The problem is that ksize() should never have existed in the first >> place. :P Every runtime bounds checker has tripped over it, and with >> the addition of the __alloc_size attribute, I had to start ripping >> ksize() out: it can't be used to pretend an allocation grew in size. >> Things need to either preallocate more or go through *realloc() like >> everything else. Luckily, ksize() is rare. >> >> FWIW, the above fix doesn't look correct to me -- I would expect this to >> be: >> >> size_t alloc_size; >> ... >> alloc_size = kmalloc_size_roundup(size + headroom + tailroom); >> data = kzalloc(alloc_size, GFP_USER); > > Making sure the struct skb_shared_info is aligned to a cache line does > not need kmalloc_size_roundup(). > > What is needed is to adjust @size so that (@size + @headroom) is a > multiple of SMP_CACHE_BYTES
ok, I'll fix it and send v2.
Thanks
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