Re: [PATCH 1/3] bpf: fix signed shift overflows in ARM JIT

[Jerin Jacob <jerinjacobk@gmail.com>]

On Tue, Nov 11, 2025 at 3:40 PM Marat Khalili <marat.khalili@huawei.com> wrote:
>
> > On Mon, Nov 10, 2025 at 9:01 PM Marat Khalili <marat.khalili@huawei.com> wrote:
> > >
> > > Left shifts of integer literals and bool values overwriting the sign bit
> > > were used multiple times in bpf_jit_arm64.c. E.g.:
> > >
> > >     insn = (!!is64) << 31;
> > >
> > > where is64 has type bool (double bang is a no-op here). The operand of
> > > left shift was promoted to type int, which when 32-bit wide cannot
> > > represent the result. Similarly literal integers have int type by
> > > default.  Sanitizer produced the following diagnostic during runtime
> > > (for various lines):
> > >
> > >     lib/bpf/bpf_jit_arm64.c:241:18: runtime error: left shift of 1 by 31
> > >     places cannot be represented in type 'int'
> >
> > Wonder why none of the tests in app/test/test_bpf.c able to catch
> > this? The generated ARM opcode looks OK (otherwise tests wont pass).
> > Could you check what is missing in the app/test/test_bpf.c?
>
> That tests do trigger it.
>
> RTE>>bpf_autotest
> ../../src/lib/bpf/bpf_jit_arm64.c:320:18: runtime error: left shift of 1 by 31 places cannot be represented in type 'int'

This is when ASAN is enabled. Right? Is it really generating BAD
opcode(i.e emiter generating bad OPcode) and test fails?


>     #0 0x22bf59c in mov_imm ../../src/lib/bpf/bpf_jit_arm64.c:320
>     #1 0x22bfae0 in emit_mov_imm ../../src/lib/bpf/bpf_jit_arm64.c:378
>     #2 0x22c3bfc in emit ../../src/lib/bpf/bpf_jit_arm64.c:1321
>     #3 0x22c4314 in __rte_bpf_jit_arm64 ../../src/lib/bpf/bpf_jit_arm64.c:1414
>     #4 0x22775c0 in __rte_bpf_jit ../../src/lib/bpf/bpf.c:44
>     #5 0x228fbdc in rte_bpf_load ../../src/lib/bpf/bpf_load.c:115
>     #6 0x6312f8 in run_test ../../src/app/test/test_bpf.c:3225
>     #7 0x631848 in test_bpf ../../src/app/test/test_bpf.c:3269
> [...]
>
> RTE>>bpf_convert_autotest
> ../../src/lib/bpf/bpf_jit_arm64.c:241:18: runtime error: left shift of 1 by 31 places cannot be represented in type 'int'
>     #0 0x22bf04c in emit_add_sub_imm ../../src/lib/bpf/bpf_jit_arm64.c:241
>     #1 0x22bf270 in emit_mov ../../src/lib/bpf/bpf_jit_arm64.c:267
>     #2 0x22bf2a4 in emit_mov_64 ../../src/lib/bpf/bpf_jit_arm64.c:273
>     #3 0x22c1a68 in emit_prologue_no_call ../../src/lib/bpf/bpf_jit_arm64.c:884
>     #4 0x22c1c9c in emit_prologue ../../src/lib/bpf/bpf_jit_arm64.c:904
>     #5 0x22c327c in emit ../../src/lib/bpf/bpf_jit_arm64.c:1136
>     #6 0x22c4314 in __rte_bpf_jit_arm64 ../../src/lib/bpf/bpf_jit_arm64.c:1414
>     #7 0x22775c0 in __rte_bpf_jit ../../src/lib/bpf/bpf.c:44
>     #8 0x228fbdc in rte_bpf_load ../../src/lib/bpf/bpf_load.c:115
>     #9 0x631e7c in test_bpf_match ../../src/app/test/test_bpf.c:3328
>     #10 0x632ce8 in test_bpf_filter_sanity ../../src/app/test/test_bpf.c:3376
>     #11 0x6331c4 in test_bpf_convert ../../src/app/test/test_bpf.c:3487
> [...]