Add compatibility workaround for programs that invalidate the packet pointer #509
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The verifier grew a check for global subprograms that invalidate the packet pointer: https://lore.kernel.org/all/[email protected]/ This affects libxdp, because the stub programs that are replaced by the user programs do not modify the packet pointer. Implement the workaround suggested in the posting above, by adding a no-op call to bpf_xdp_adjust_tail() to the stub programs being replaced. This does not affect performance, nor backwards compatibility of the dispatcher, since the stub programs are never actually executed when libxdp is used. The only effect will be that on newer kernels, a version of libxdp that includes these changes will work with programs that modify the packet pointer, while older versions of libxdp won't. Signed-off-by: Toke Høiland-Jørgensen <[email protected]>
… pointer Newer versions of the kernel disallow attaching freplace programs that modify the packet pointer on top of functions that don't. The libxdp dispatcher was updated to include a workaround for this, so let's add a test that exercises this workaround. Signed-off-by: Toke Høiland-Jørgensen <[email protected]>
The 6.14 kernel introduced the change that disallows attaching programs that modify the packet pointer on top of functions that don't, so let's add that version to the test matrix so we exercise the workaround. Signed-off-by: Toke Høiland-Jørgensen <[email protected]>
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Newer kernels added checks that disallow replacing functions that don't modify
the packet pointer with ones that do. For libxdp this means that programs that
modify the packet pointer refuses to load. Fix this by adding the recommended
workaround to the dispatcher program.
Fixes #503