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| author | Daniel Borkmann <daniel@iogearbox.net> | 2021-04-30 16:21:46 +0200 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2021-05-03 11:56:16 +0200 |
| commit | b9b34ddbe2076ade359cd5ce7537d5ed019e9807 (patch) | |
| tree | 49fcb2249efc10349d019d367f66d41274edf448 /kernel | |
| parent | f80f88f0e2f2ef9cd805fad1bbf676b0ecd4b55c (diff) | |
| download | linux-b9b34ddbe2076ade359cd5ce7537d5ed019e9807.tar.gz linux-b9b34ddbe2076ade359cd5ce7537d5ed019e9807.tar.bz2 linux-b9b34ddbe2076ade359cd5ce7537d5ed019e9807.zip | |
bpf: Fix masking negation logic upon negative dst register
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: 979d63d50c0c ("bpf: prevent out of bounds speculation on pointer arithmetic")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Piotr Krysiuk <piotras@gmail.com>
Reviewed-by: Piotr Krysiuk <piotras@gmail.com>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/bpf/verifier.c | 12 |
1 files changed, 4 insertions, 8 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 8fd552c16763..db347fb125e3 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -12391,14 +12391,10 @@ static int do_misc_fixups(struct bpf_verifier_env *env) *patch++ = BPF_ALU64_REG(BPF_OR, BPF_REG_AX, off_reg); *patch++ = BPF_ALU64_IMM(BPF_NEG, BPF_REG_AX, 0); *patch++ = BPF_ALU64_IMM(BPF_ARSH, BPF_REG_AX, 63); - if (issrc) { - *patch++ = BPF_ALU64_REG(BPF_AND, BPF_REG_AX, - off_reg); - insn->src_reg = BPF_REG_AX; - } else { - *patch++ = BPF_ALU64_REG(BPF_AND, off_reg, - BPF_REG_AX); - } + *patch++ = BPF_ALU64_REG(BPF_AND, BPF_REG_AX, off_reg); + if (!issrc) + *patch++ = BPF_MOV64_REG(insn->dst_reg, insn->src_reg); + insn->src_reg = BPF_REG_AX; if (isneg) insn->code = insn->code == code_add ? code_sub : code_add; |