On 9/11/24 11:54 PM, kernel test robot wrote:
Hi Yonghong,
kernel test robot noticed the following build warnings:
[auto build test WARNING on bpf-next/master]
url: https://github.com/intel-lab-lkp/linux/commits/Yonghong-Song/selftests-bpf-Add-a-couple-of-tests-for-potential-sdiv-overflow/20240911-124236
base: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
patch link: https://lore.kernel.org/r/20240911044017.2261738-1-yonghong.song%40linux.dev
patch subject: [PATCH bpf-next 1/2] bpf: Fix a sdiv overflow issue
config: x86_64-randconfig-121-20240912 (https://download.01.org/0day-ci/archive/20240912/202409121439.L01ZquSs-lkp@xxxxxxxxx/config)
compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240912/202409121439.L01ZquSs-lkp@xxxxxxxxx/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-kbuild-all/202409121439.L01ZquSs-lkp@xxxxxxxxx/
sparse warnings: (new ones prefixed by >>)
kernel/bpf/verifier.c:21184:38: sparse: sparse: subtraction of functions? Share your drugs
kernel/bpf/verifier.c: note: in included file (through include/linux/bpf.h, include/linux/bpf-cgroup.h):
include/linux/bpfptr.h:65:40: sparse: sparse: cast to non-scalar
include/linux/bpfptr.h:65:40: sparse: sparse: cast from non-scalar
include/linux/bpfptr.h:65:40: sparse: sparse: cast to non-scalar
include/linux/bpfptr.h:65:40: sparse: sparse: cast from non-scalar
include/linux/bpfptr.h:65:40: sparse: sparse: cast to non-scalar
include/linux/bpfptr.h:65:40: sparse: sparse: cast from non-scalar
kernel/bpf/verifier.c:20538:33: sparse: sparse: cast truncates bits from constant value (8000000000000000 becomes 0)
The above is expected. See below macro definition in include/linux/filter.h
/* BPF_LD_IMM64 macro encodes single 'load 64-bit immediate' insn */
#define BPF_LD_IMM64(DST, IMM) \
BPF_LD_IMM64_RAW(DST, 0, IMM)
#define BPF_LD_IMM64_RAW(DST, SRC, IMM) \
((struct bpf_insn) { \
.code = BPF_LD | BPF_DW | BPF_IMM, \
.dst_reg = DST, \
.src_reg = SRC, \
.off = 0, \
.imm = (__u32) (IMM) }), \
((struct bpf_insn) { \
.code = 0, /* zero is reserved opcode */ \
.dst_reg = 0, \
.src_reg = 0, \
.off = 0, \
.imm = ((__u64) (IMM)) >> 32 })
So (__u32) (IMM) will cause a truncation and may cause a warning,
but it is expected for bpf.
include/linux/bpfptr.h:65:40: sparse: sparse: cast to non-scalar
include/linux/bpfptr.h:65:40: sparse: sparse: cast from non-scalar
vim +20538 kernel/bpf/verifier.c
20445
20446 /* Do various post-verification rewrites in a single program pass.
20447 * These rewrites simplify JIT and interpreter implementations.
20448 */
20449 static int do_misc_fixups(struct bpf_verifier_env *env)
20450 {
20451 struct bpf_prog *prog = env->prog;
20452 enum bpf_attach_type eatype = prog->expected_attach_type;
20453 enum bpf_prog_type prog_type = resolve_prog_type(prog);
20454 struct bpf_insn *insn = prog->insnsi;
20455 const struct bpf_func_proto *fn;
20456 const int insn_cnt = prog->len;
20457 const struct bpf_map_ops *ops;
20458 struct bpf_insn_aux_data *aux;
20459 struct bpf_insn *insn_buf = env->insn_buf;
20460 struct bpf_prog *new_prog;
20461 struct bpf_map *map_ptr;
20462 int i, ret, cnt, delta = 0, cur_subprog = 0;
20463 struct bpf_subprog_info *subprogs = env->subprog_info;
20464 u16 stack_depth = subprogs[cur_subprog].stack_depth;
20465 u16 stack_depth_extra = 0;
20466
20467 if (env->seen_exception && !env->exception_callback_subprog) {
20468 struct bpf_insn patch[] = {
20469 env->prog->insnsi[insn_cnt - 1],
20470 BPF_MOV64_REG(BPF_REG_0, BPF_REG_1),
20471 BPF_EXIT_INSN(),
20472 };
20473
20474 ret = add_hidden_subprog(env, patch, ARRAY_SIZE(patch));
20475 if (ret < 0)
20476 return ret;
20477 prog = env->prog;
20478 insn = prog->insnsi;
20479
20480 env->exception_callback_subprog = env->subprog_cnt - 1;
20481 /* Don't update insn_cnt, as add_hidden_subprog always appends insns */
20482 mark_subprog_exc_cb(env, env->exception_callback_subprog);
20483 }
20484
20485 for (i = 0; i < insn_cnt;) {
20486 if (insn->code == (BPF_ALU64 | BPF_MOV | BPF_X) && insn->imm) {
20487 if ((insn->off == BPF_ADDR_SPACE_CAST && insn->imm == 1) ||
20488 (((struct bpf_map *)env->prog->aux->arena)->map_flags & BPF_F_NO_USER_CONV)) {
20489 /* convert to 32-bit mov that clears upper 32-bit */
20490 insn->code = BPF_ALU | BPF_MOV | BPF_X;
20491 /* clear off and imm, so it's a normal 'wX = wY' from JIT pov */
20492 insn->off = 0;
20493 insn->imm = 0;
20494 } /* cast from as(0) to as(1) should be handled by JIT */
20495 goto next_insn;
20496 }
20497
20498 if (env->insn_aux_data[i + delta].needs_zext)
20499 /* Convert BPF_CLASS(insn->code) == BPF_ALU64 to 32-bit ALU */
20500 insn->code = BPF_ALU | BPF_OP(insn->code) | BPF_SRC(insn->code);
20501
20502 /* Make divide-by-zero exceptions impossible. */
20503 if (insn->code == (BPF_ALU64 | BPF_MOD | BPF_X) ||
20504 insn->code == (BPF_ALU64 | BPF_DIV | BPF_X) ||
20505 insn->code == (BPF_ALU | BPF_MOD | BPF_X) ||
20506 insn->code == (BPF_ALU | BPF_DIV | BPF_X)) {
20507 bool is64 = BPF_CLASS(insn->code) == BPF_ALU64;
20508 bool isdiv = BPF_OP(insn->code) == BPF_DIV;
20509 bool is_sdiv64 = is64 && isdiv && insn->off == 1;
20510 struct bpf_insn *patchlet;
20511 struct bpf_insn chk_and_div[] = {
20512 /* [R,W]x div 0 -> 0 */
20513 BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
20514 BPF_JNE | BPF_K, insn->src_reg,
20515 0, 2, 0),
20516 BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg),
20517 BPF_JMP_IMM(BPF_JA, 0, 0, 1),
20518 *insn,
20519 };
20520 struct bpf_insn chk_and_mod[] = {
20521 /* [R,W]x mod 0 -> [R,W]x */
20522 BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
20523 BPF_JEQ | BPF_K, insn->src_reg,
20524 0, 1 + (is64 ? 0 : 1), 0),
20525 *insn,
20526 BPF_JMP_IMM(BPF_JA, 0, 0, 1),
20527 BPF_MOV32_REG(insn->dst_reg, insn->dst_reg),
20528 };
20529 struct bpf_insn chk_and_sdiv64[] = {
20530 /* Rx sdiv 0 -> 0 */
20531 BPF_RAW_INSN(BPF_JMP | BPF_JNE | BPF_K, insn->src_reg,
20532 0, 2, 0),
20533 BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg),
20534 BPF_JMP_IMM(BPF_JA, 0, 0, 8),
20535 /* LLONG_MIN sdiv -1 -> LLONG_MIN */
20536 BPF_RAW_INSN(BPF_JMP | BPF_JNE | BPF_K, insn->src_reg,
20537 0, 6, -1),
20538 BPF_LD_IMM64(insn->src_reg, LLONG_MIN),
the warning is triggered here.
20539 BPF_RAW_INSN(BPF_JMP | BPF_JNE | BPF_X, insn->dst_reg,
20540 insn->src_reg, 2, 0),
20541 BPF_MOV64_IMM(insn->src_reg, -1),
20542 BPF_JMP_IMM(BPF_JA, 0, 0, 2),
20543 BPF_MOV64_IMM(insn->src_reg, -1),
20544 *insn,
20545 };
20546
[...]
