Messages in this thread | | | Date | Tue, 14 Oct 2014 13:13:38 -0400 (EDT) | Subject | Re: [PATCH v2 net] x86: bpf_jit: fix two bugs in eBPF JIT compiler | From | David Miller <> |
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From: Alexei Starovoitov <ast@plumgrid.com> Date: Fri, 10 Oct 2014 20:30:23 -0700
> 1. > JIT compiler using multi-pass approach to converge to final image size, > since x86 instructions are variable length. It starts with large > gaps between instructions (so some jumps may use imm32 instead of imm8) > and iterates until total program size is the same as in previous pass. > This algorithm works only if program size is strictly decreasing. > Programs that use LD_ABS insn need additional code in prologue, but it > was not emitted during 1st pass, so there was a chance that 2nd pass would > adjust imm32->imm8 jump offsets to the same number of bytes as increase in > prologue, which may cause algorithm to erroneously decide that size converged. > Fix it by always emitting largest prologue in the first pass which > is detected by oldproglen==0 check. > Also change error check condition 'proglen != oldproglen' to fail gracefully. > > 2. > while staring at the code realized that 64-byte buffer may not be enough > when 1st insn is large, so increase it to 128 to avoid buffer overflow > (theoretical maximum size of prologue+div is 109) and add runtime check. > > Fixes: 622582786c9e ("net: filter: x86: internal BPF JIT") > Reported-by: Darrick J. Wong <darrick.wong@oracle.com> > Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> > --- > v1->v2: reduce chances of stack corruption in case of future bugs (suggested by Eric) > > note in classic BPF programs 1st insn is always short move, but native eBPF > programs may trigger buffer overflow. I couldn't force the crash with overflow, > since there are no further calls while this part of stack is used. > Both are ugly bugs regardless. > When net-next opens I will add narrowed down testcase from 'nmap' to testsuite.
Applied, thanks Alexei.
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