On Fri, Nov 06, 2015 at 09:36:17PM -0800, Yang Shi wrote: > ARM64 JIT used FP (x29) as eBPF fp register, but FP is subjected to > change during function call so it may cause the BPF prog stack base address > change too. Whenever, it pointed to the bottom of BPF prog stack instead of > the top. > > So, when copying data via bpf_probe_read, it will be copied to (SP - offset), > then it may overwrite the saved FP/LR. > > Use x25 to replace FP as BPF stack base register (fp). Since x25 is callee > saved register, so it will keep intact during function call. > It is initialized in BPF prog prologue when BPF prog is started to run > everytime. When BPF prog exits, it could be just tossed. > > Other than this the BPf prog stack base need to be setup before function > call stack. > > So, the BPF stack layout looks like: > > high > original A64_SP => 0:+-----+ BPF prologue > | | FP/LR and callee saved registers > BPF fp register => +64:+-----+ > | | > | ... | BPF prog stack > | | > | | > current A64_SP => +-----+ > | | > | ... | Function call stack > | | > +-----+ > low > > Signed-off-by: Yang Shi <yang....@linaro.org> > CC: Zi Shen Lim <zlim....@gmail.com> > CC: Xi Wang <xi.w...@gmail.com>
Thanks for tracking it down. That looks like fundamental bug in arm64 jit. I'm surprised function calls worked at all. Zi please review. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
