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  1. May 24, 2021
  3. May 22, 2021
  5. May 21, 2021
  7. May 18, 2021
    • Daniel Borkmann's avatar
      bpf: Fix leakage of uninitialized bpf stack under speculation · 1fdb52d9
      Daniel Borkmann authored 
      
mainline inclusion
from mainline-v5.13-rc1
commit 801c6058d14a82179a7ee17a4b532cac6fad067f
category: bugfix
bugzilla: NA
CVE: CVE-2021-31829

--------------------------------

The current implemented mechanisms to mitigate data disclosure under
speculation mainly address stack and map value oob access from the
speculative domain. However, Piotr discovered that uninitialized BPF
stack is not protected yet, and thus old data from the kernel stack,
potentially including addresses of kernel structures, could still be
extracted from that 512 bytes large window. The BPF stack is special
compared to map values since it's not zero initialized for every
program invocation, whereas map values /are/ zero initialized upon
their initial allocation and thus cannot leak any prior data in either
domain. In the non-speculative domain, the verifier ensures that every
stack slot read must have a prior stack slot write by the BPF program
to avoid such data leaking issue.

However, this is not enough: for example, when the pointer arithmetic
operation moves the stack pointer from the last valid stack offset to
the first valid offset, the sanitation logic allows for any intermediate
offsets during speculative execution, which could then be used to
extract any restricted stack content via side-channel.

Given for unprivileged stack pointer arithmetic the use of unknown
but bounded scalars is generally forbidden, we can simply turn the
register-based arithmetic operation into an immediate-based arithmetic
operation without the need for masking. This also gives the benefit
of reducing the needed instructions for the operation. Given after
the work in 7fedb63a8307 ("bpf: Tighten speculative pointer arithmetic
mask"), the aux->alu_limit already holds the final immediate value for
the offset register with the known scalar. Thus, a simple mov of the
immediate to AX register with using AX as the source for the original
instruction is sufficient and possible now in this case.

Reported-by: default avatarPiotr Krysiuk <piotras@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Tested-by: default avatarPiotr Krysiuk <piotras@gmail.com>
Reviewed-by: default avatarPiotr Krysiuk <piotras@gmail.com>
Reviewed-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Conflicts:
  kernel/bpf/verifier.c
Signed-off-by: default avatarYang Yingliang <yangyingliang@huawei.com>
Reviewed-by: default avatarXiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: default avatarKuohai Xu <xukuohai@huawei.com>
Signed-off-by: default avatarYang Yingliang <yangyingliang@huawei.com>
      1fdb52d9
    • Daniel Borkmann's avatar
      bpf: Fix masking negation logic upon negative dst register · f8eafed4
      Daniel Borkmann authored 
      
stable inclusion
from linux-4.19.190
commit 0e2dfdc74a7f4036127356d42ea59388f153f42c

--------------------------------

commit b9b34ddbe2076ade359cd5ce7537d5ed019e9807 upstream.

The negation logic for the case where the off_reg is sitting in the
dst register is not correct given then we cannot just invert the add
to a sub or vice versa. As a fix, perform the final bitwise and-op
unconditionally into AX from the off_reg, then move the pointer from
the src to dst and finally use AX as the source for the original
pointer arithmetic operation such that the inversion yields a correct
result. The single non-AX mov in between is possible given constant
blinding is retaining it as it's not an immediate based operation.

Fixes: 979d63d5 ("bpf: prevent out of bounds speculation on pointer arithmetic")
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Tested-by: default avatarPiotr Krysiuk <piotras@gmail.com>
Reviewed-by: default avatarPiotr Krysiuk <piotras@gmail.com>
Reviewed-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarYang Yingliang <yangyingliang@huawei.com>
      f8eafed4
  9. May 17, 2021
  11. May 14, 2021