From: Yazhou Tang Add a selftest to verify the verifier and JIT behavior when handling bpf-to-bpf calls with relative jump offsets exceeding the s16 boundary. The test utilizes an inline assembly block with ".rept 32765" to generate a massive dummy subprogram. By placing this padding between the main program and the target subprogram, it forces the verifier to process a bpf-to-bpf call where the imm field exceeds the s16 range. - When JIT is enabled, it asserts that the program is successfully loaded and executes correctly to return the expected value. Since patch 1/2 does not change the JIT behavior, the test passes whether the fix is applied or not. - When JIT is disabled, it also asserts that the program is successfully loaded and executes correctly to return the expected value 3. - Before the fix, the verifier rewrites the call instruction with a truncated offset (here 32768 -> -32768) and lets it pass. When the program is executed, the call instruction will go to a wrong target (the landing pad) instead of the intended subprogram, then return -1 and fail. - After the fix, the verifier correctly handles the large offset and allows it to pass. The program then executes correctly to return the expected value 3. Co-developed-by: Tianci Cao Signed-off-by: Tianci Cao Co-developed-by: Shenghao Yuan Signed-off-by: Shenghao Yuan Signed-off-by: Yazhou Tang --- .../selftests/bpf/prog_tests/verifier.c | 2 + .../bpf/progs/verifier_call_large_imm.c | 66 +++++++++++++++++++ 2 files changed, 68 insertions(+) create mode 100644 tools/testing/selftests/bpf/progs/verifier_call_large_imm.c diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c index a96b25ebff23..b27f4d4e2bd4 100644 --- a/tools/testing/selftests/bpf/prog_tests/verifier.c +++ b/tools/testing/selftests/bpf/prog_tests/verifier.c @@ -22,6 +22,7 @@ #include "verifier_bswap.skel.h" #include "verifier_btf_ctx_access.skel.h" #include "verifier_btf_unreliable_prog.skel.h" +#include "verifier_call_large_imm.skel.h" #include "verifier_cfg.skel.h" #include "verifier_cgroup_inv_retcode.skel.h" #include "verifier_cgroup_skb.skel.h" @@ -170,6 +171,7 @@ void test_verifier_bpf_trap(void) { RUN(verifier_bpf_trap); } void test_verifier_bswap(void) { RUN(verifier_bswap); } void test_verifier_btf_ctx_access(void) { RUN(verifier_btf_ctx_access); } void test_verifier_btf_unreliable_prog(void) { RUN(verifier_btf_unreliable_prog); } +void test_verifier_call_large_imm(void) { RUN(verifier_call_large_imm); } void test_verifier_cfg(void) { RUN(verifier_cfg); } void test_verifier_cgroup_inv_retcode(void) { RUN(verifier_cgroup_inv_retcode); } void test_verifier_cgroup_skb(void) { RUN(verifier_cgroup_skb); } diff --git a/tools/testing/selftests/bpf/progs/verifier_call_large_imm.c b/tools/testing/selftests/bpf/progs/verifier_call_large_imm.c new file mode 100644 index 000000000000..1e2c8addc582 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/verifier_call_large_imm.c @@ -0,0 +1,66 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include "bpf_misc.h" + +int call_happened = 0; + +/* + * 32765 is the exact minimum number of padding instructions needed to + * trigger the verifier failure, because: + * 1. Counting the wrapper instructions around the padding block (one + * "r0=0" and two "exit" instructions), the actual jump distance + * evaluates to N + 3. + * 2. To overflow the s16 max bound (32767), we need N + 3 > 32767. + * Thus, N = 32765 is the exact minimum padding size required. + */ +static __attribute__((noinline)) void padding_subprog(void) +{ + asm volatile ( + "r0 = 0;" + ".rept 32765;" + "r0 += 0;" + ".endr;" + ::: "r0"); +} + +static __attribute__((noinline)) int target_subprog(void) +{ + /* A volatile variable is used here to prevent optimization. */ + volatile int magic_ret = 3; + return magic_ret; +} + +SEC("syscall") +__success __retval(3) +int call_large_imm_test(void *ctx) +{ + /* + * Landing pad to handle call error on kernel without the fix, + * preventing kernel panic. + */ + asm volatile ( + "r0 = 0;" + ".rept 32768;" + "r0 += 0;" + ".endr;" + ::: "r0"); + + /* + * The call_happened variable is 1 only when the call insn wrongly + * go back to the landing pad above. + */ + if (call_happened == 1) { + /* A volatile variable is used here to prevent optimization. */ + volatile int flag = -1; + return flag; + } + + call_happened = 1; + + padding_subprog(); + + return target_subprog(); +} + +char LICENSE[] SEC("license") = "GPL"; -- 2.54.0