bpf: Derive the atomic load register in one place

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check_atomic_rmw() open codes the mapping from a BPF_ATOMIC to the register
it reads the old value into, the BPF_STX case of insn_def_regno() open codes
the very same mapping a second time, the const folding and the liveness
transfer functions a third and a fourth time, and BPF JITs need it as well
to know which register a faulting BPF_PROBE_ATOMIC has to clear.

Add a small helper so that all of them can share it. No functional change.
The BPF_LOAD_ACQ case is there for the JITs, which do walk all instruction
classes. const_reg_xfer() loses its explicit BPF_ATOMIC mode test since the
helper checks class and mode itself; the BPF_PROBE_ATOMIC it additionally
accepts cannot be seen there as it is only set from bpf_do_misc_fixups(),
that is, after const folding has run. arg_track_xfer() keeps its mode test
since that also guards the stack clearing next to it.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://patch.msgid.link/20260811131600.506721-1-daniel@iogearbox.net
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>

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Daniel Borkmann 2026-08-11 15:15:55 +02:00 • committed by Eduard Zingerman

parent 07cb86aa50

commit 41c5dbb4be

5 changed files with 33 additions and 35 deletions

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24

include/linux/filter.h

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11

kernel/bpf/const_fold.c

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11

kernel/bpf/fixups.c

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9

kernel/bpf/liveness.c

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13

kernel/bpf/verifier.c

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