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Alexei Starovoitov
270954791c
Philo Lu says:
====================
bpf: allow bpf_for_each_map_elem() helper with different input maps
Currently, taking different maps within a single bpf_for_each_map_elem
call is not allowed. For example the following codes cannot pass the
verifier (with error "tail_call abusing map_ptr"):
```
static void test_by_pid(int pid)
{
if (pid <= 100)
bpf_for_each_map_elem(&map1, map_elem_cb, NULL, 0);
else
bpf_for_each_map_elem(&map2, map_elem_cb, NULL, 0);
}
```
This is because during bpf_for_each_map_elem verifying,
bpf_insn_aux_data->map_ptr_state is expected as map_ptr (instead of poison
state), which is then needed by set_map_elem_callback_state. However, as
there are two different map ptr input, map_ptr_state is marked as
BPF_MAP_PTR_POISON, and thus the second map_ptr would be lost.
BPF_MAP_PTR_POISON is also needed by bpf_for_each_map_elem to skip
retpoline optimization in do_misc_fixups(). Therefore, map_ptr_state and
map_ptr are both needed for bpf_for_each_map_elem.
This patchset solves it by transform bpf_insn_aux_data->map_ptr_state as a
new struct, storing poison/unpriv state and map pointer together without
additional memory overhead. Then bpf_for_each_map_elem works well with
different input maps. It also makes map_ptr_state logic clearer.
A test case is added to selftest, which would fail to load without this
patchset.
Changelogs
-> v1:
- PATCH 1/3:
- make the commit log clearer
- change poison and unpriv to bool in struct bpf_map_ptr_state, also the
return value in bpf_map_ptr_poisoned() and bpf_map_ptr_unpriv()
- PATCH 2/3:
- change the comments in set_map_elem_callback_state()
- PATCH 3/3:
- remove the "skipping the last element" logic during map updating
- change if() to ASSERT_OK()
Please review, thanks.
====================
Link: https://lore.kernel.org/r/20240405025536.18113-1-lulie@linux.alibaba.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
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be rendered in a number of formats, like HTML and PDF. Please read
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In order to build the documentation, use ``make htmldocs`` or
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
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the problems which may result by upgrading your kernel.