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selftests/bpf: BPF_PSEUDO_FUNC reference to the main program

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Add a test case for a BPF_PSEUDO_FUNC load instruction that references
the entry function of the program it belongs to. W/o the previous
patch the verifier accepts this program thus allowing a runtime call
at a bogus address. See previous patch for detailed description.

Main function needs to be marked with BTF_FUNC_STATIC for the test to
trigger the bug, the patch uses test_verifier harness instead of
test_prog because libbpf has no way to convey this.

Reported-by: Nicholas Carlini <npc@anthropic.com>
Suggested-by: Nicholas Carlini <npc@anthropic.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260902233658.1186477-2-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Eduard Zingerman
2026-09-02 16:36:58 -07:00
committed by Alexei Starovoitov
parent 374b2c5561
commit ac0aaef0aa
1 changed files with 45 additions and 0 deletions
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45
tools/testing/selftests/bpf/verifier/pseudo_func.c Normal file
View File

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/*
* Buggy verifier accepted the program below while not patching BPF_PSEUDO_FUNC
* load instruction to contain a real address. Which resulted in a function call
* to a bogus address.
*/
{
"BPF_PSEUDO_FUNC reference to the main program",
.insns = {
/* r6 = bpf_map_lookup_elem(&timer_map, &(int){0}); */
BPF_ST_MEM(BPF_W, BPF_REG_10, -4, 0),
BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4),
BPF_LD_MAP_FD(BPF_REG_1, 0),
BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 10),
BPF_MOV64_REG(BPF_REG_6, BPF_REG_0),
/* bpf_timer_init(r6, &timer_map, 0); */
BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
BPF_LD_MAP_FD(BPF_REG_2, 0),
BPF_MOV64_IMM(BPF_REG_3, 0),
BPF_EMIT_CALL(BPF_FUNC_timer_init),
/* bpf_timer_set_callback(r6, <insn #0>); */
BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
BPF_RAW_INSN(BPF_LD | BPF_IMM | BPF_DW, BPF_REG_2, BPF_PSEUDO_FUNC, 0, -15),
BPF_RAW_INSN(0, 0, 0, 0, 0),
BPF_EMIT_CALL(BPF_FUNC_timer_set_callback),
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
},
.prog_type = BPF_PROG_TYPE_TRACEPOINT,
.fixup_map_timer = { 3, 9 },
.result = REJECT,
.errstr = "callback function cannot be the main program",
.func_info = { { 0, 4 /* main_prog */ } },
.func_info_cnt = 1,
.btf_strings = "\0int\0ctx\0main_prog",
.btf_types = {
/* 1: int */ BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4),
/* 2: void* */ BTF_PTR_ENC(0),
/* 3: int __(void *) */ BTF_FUNC_PROTO_ENC(1, 1),
BTF_FUNC_PROTO_ARG_ENC(5, 2),
/* 4: main_prog */ BTF_FUNC_ENC(9, 3),
BTF_END_RAW
}
},