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| author | Jose E. Marchesi <jose.marchesi@oracle.com> | 2024-05-08 12:35:51 +0200 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2024-05-08 09:56:30 -0700 |
| commit | 1209a523f6914404e8941d9e04caa42be7cab8d5 (patch) | |
| tree | c69b8da8a03710c98bf85ec6f9da01f214373ba0 /tools/testing/selftests/bpf/Makefile | |
| parent | cd3fc3b9782130a5bc1dc3dfccffbc1657637a93 (diff) | |
bpf: avoid UB in usages of the __imm_insn macro
[Changes from V2:
- no-strict-aliasing is only applied when building with GCC.
- cpumask_failure.c is excluded, as it doesn't use __imm_insn.]
The __imm_insn macro is defined in bpf_misc.h as:
#define __imm_insn(name, expr) [name]"i"(*(long *)&(expr))
This may lead to type-punning and strict aliasing rules violations in
it's typical usage where the address of a struct bpf_insn is passed as
expr, like in:
__imm_insn(st_mem,
BPF_ST_MEM(BPF_W, BPF_REG_1, offsetof(struct __sk_buff, mark), 42))
Where:
#define BPF_ST_MEM(SIZE, DST, OFF, IMM) \
((struct bpf_insn) { \
.code = BPF_ST | BPF_SIZE(SIZE) | BPF_MEM, \
.dst_reg = DST, \
.src_reg = 0, \
.off = OFF, \
.imm = IMM })
In all the actual instances of this in the BPF selftests the value is
fed to a volatile asm statement as soon as it gets read from memory,
and thus it is unlikely anti-aliasing rules breakage may lead to
misguided optimizations.
However, GCC detects the potential problem (indirectly) by issuing a
warning stating that a temporary <Uxxxxxx> is used uninitialized,
where the temporary corresponds to the memory read by *(long *).
This patch adds -fno-strict-aliasing to the compilation flags of the
particular selftests that do type punning via __imm_insn, only for
GCC.
Tested in master bpf-next.
No regressions.
Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
Cc: david.faust@oracle.com
Cc: cupertino.miranda@oracle.com
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240508103551.14955-1-jose.marchesi@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'tools/testing/selftests/bpf/Makefile')
| -rw-r--r-- | tools/testing/selftests/bpf/Makefile | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index 511ea84139a3..e962a0bd8a78 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -86,6 +86,19 @@ progs/btf_dump_test_case_namespacing.c-bpf_gcc-CFLAGS := -Wno-error progs/btf_dump_test_case_packing.c-bpf_gcc-CFLAGS := -Wno-error progs/btf_dump_test_case_padding.c-bpf_gcc-CFLAGS := -Wno-error progs/btf_dump_test_case_syntax.c-bpf_gcc-CFLAGS := -Wno-error + +# The following tests do type-punning, via the __imm_insn macro, from +# `struct bpf_insn' to long and then uses the value. This triggers an +# "is used uninitialized" warning in GCC due to strict-aliasing +# rules. +progs/verifier_ref_tracking.c-bpf_gcc-CFLAGS := -fno-strict-aliasing +progs/verifier_unpriv.c-bpf_gcc-CFLAGS := -fno-strict-aliasing +progs/verifier_cgroup_storage.c-bpf_gcc-CFLAGS := -fno-strict-aliasing +progs/verifier_ld_ind.c-bpf_gcc-CFLAGS := -fno-strict-aliasing +progs/verifier_map_ret_val.c-bpf_gcc-CFLAGS := -fno-strict-aliasing +progs/verifier_spill_fill.c-bpf_gcc-CFLAGS := -fno-strict-aliasing +progs/verifier_subprog_precision.c-bpf_gcc-CFLAGS := -fno-strict-aliasing +progs/verifier_uninit.c-bpf_gcc-CFLAGS := -fno-strict-aliasing endif ifneq ($(CLANG_CPUV4),) |