bpf: Recognize addr_space_cast instruction in the verifier.

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rY = addr_space_cast(rX, 0, 1) tells the verifier that rY->type = PTR_TO_ARENA.
Any further operations on PTR_TO_ARENA register have to be in 32-bit domain.

The verifier will mark load/store through PTR_TO_ARENA with PROBE_MEM32.
JIT will generate them as kern_vm_start + 32bit_addr memory accesses.

rY = addr_space_cast(rX, 1, 0) tells the verifier that rY->type = unknown scalar.
If arena->map_flags has BPF_F_NO_USER_CONV set then convert cast_user to mov32 as well.
Otherwise JIT will convert it to:
  rY = (u32)rX;
  if (rY)
     rY |= arena->user_vm_start & ~(u64)~0U;

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240308010812.89848-6-alexei.starovoitov@gmail.com

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This commit is contained in:

Alexei Starovoitov 2024-03-07 17:08:03 -08:00 • committed by Andrii Nakryiko

parent 142fd4d2dc

commit 6082b6c328

5 changed files with 109 additions and 9 deletions

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1

include/linux/bpf.h

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1

include/linux/bpf_verifier.h

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3

kernel/bpf/log.c

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6

kernel/bpf/syscall.c

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107

kernel/bpf/verifier.c

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