Commit 62ccdb11 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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selftests/bpf: add edge case backtracking logic test 



Add a dedicated selftests to try to set up conditions to have a state
with same first and last instruction index, but it actually is a loop
3->4->1->2->3. This confuses mark_chain_precision() if verifier doesn't
take into account jump history.

Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231110002638.4168352-4-andrii@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 4bb7ea94

tools/testing/selftests/bpf/progs/verifier_precision.c

+40 −0
Original line number Diff line number Diff line
@@ -91,3 +91,43 @@ __naked int bpf_end_bswap(void) 
}



#endif /* v4 instruction */



SEC("?raw_tp")

__success __log_level(2)

/*

 * Without the bug fix there will be no history between "last_idx 3 first_idx 3"

 * and "parent state regs=" lines. "R0_w=6" parts are here to help anchor

 * expected log messages to the one specific mark_chain_precision operation.

 *

 * This is quite fragile: if verifier checkpointing heuristic changes, this

 * might need adjusting.

 */

__msg("2: (07) r0 += 1                       ; R0_w=6")

__msg("3: (35) if r0 >= 0xa goto pc+1")

__msg("mark_precise: frame0: last_idx 3 first_idx 3 subseq_idx -1")

__msg("mark_precise: frame0: regs=r0 stack= before 2: (07) r0 += 1")

__msg("mark_precise: frame0: regs=r0 stack= before 1: (07) r0 += 1")

__msg("mark_precise: frame0: regs=r0 stack= before 4: (05) goto pc-4")

__msg("mark_precise: frame0: regs=r0 stack= before 3: (35) if r0 >= 0xa goto pc+1")

__msg("mark_precise: frame0: parent state regs= stack=:  R0_rw=P4")

__msg("3: R0_w=6")

__naked int state_loop_first_last_equal(void)

{

	asm volatile (

		"r0 = 0;"

	"l0_%=:"

		"r0 += 1;"

		"r0 += 1;"

		/* every few iterations we'll have a checkpoint here with

		 * first_idx == last_idx, potentially confusing precision

		 * backtracking logic

		 */

		"if r0 >= 10 goto l1_%=;"	/* checkpoint + mark_precise */

		"goto l0_%=;"

	"l1_%=:"

		"exit;"

		::: __clobber_common

	);

}



char _license[] SEC("license") = "GPL";