From: Daniel Borkmann <dan...@iogearbox.net>
Date: Tue, 28 Jul 2015 15:26:36 +0200
> With eBPF JIT compiler enabled on x86_64, I was able to reliably trigger
> the following general protection fault out of an eBPF program with a simple
> tail call, f.e. tracex5 (or a stripped down version of it):
...
> Changing the emitter to always use the 4 byte displacement in the lea
> instruction fixes the panic on my side. It increases the tail call instruction
> emission by 3 more byte, but it should cover us from various combinations
> (and perhaps other future increases on related structures).
>
> After patch, disassembly:
>
> [...]
> 9e: lea 0x80(%rsi,%rdx,8),%rax <--- CONFIG_LOCKDEP/CONFIG_LOCK_STAT
> 48 8d 84 d6 80 00 00 00
> a6: mov (%rax),%rax
> 48 8b 00
> [...]
>
> [...]
> 9e: lea 0x50(%rsi,%rdx,8),%rax <--- No CONFIG_LOCKDEP
> 48 8d 84 d6 50 00 00 00
> a6: mov (%rax),%rax
> 48 8b 00
> [...]
>
> Fixes: b52f00e6a715 ("x86: bpf_jit: implement bpf_tail_call() helper")
> Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
Applied, thanks.
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