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dkim=pass header.d=google.com header.s=20210112 header.b=Q0MGEOK+; spf=pass (imf23.hostedemail.com: domain of edumazet@google.com designates 209.85.128.169 as permitted sender) smtp.mailfrom=edumazet@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam03 X-Rspam-User: X-HE-Tag: 1667363842-904691 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Nov 1, 2022 at 9:27 PM Kees Cook 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 > > > >> --- > > > >> 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