From 5dd9cdbc9dec3e99b19e483767e247d15ca8cc0d Mon Sep 17 00:00:00 2001 From: Eduard Zingerman Date: Fri, 9 Dec 2022 15:57:29 +0200 Subject: bpf: states_equal() must build idmap for all function frames verifier.c:states_equal() must maintain register ID mapping across all function frames. Otherwise the following example might be erroneously marked as safe: main: fp[-24] = map_lookup_elem(...) ; frame[0].fp[-24].id == 1 fp[-32] = map_lookup_elem(...) ; frame[0].fp[-32].id == 2 r1 = &fp[-24] r2 = &fp[-32] call foo() r0 = 0 exit foo: 0: r9 = r1 1: r8 = r2 2: r7 = ktime_get_ns() 3: r6 = ktime_get_ns() 4: if (r6 > r7) goto skip_assign 5: r9 = r8 skip_assign: ; <--- checkpoint 6: r9 = *r9 ; (a) frame[1].r9.id == 2 ; (b) frame[1].r9.id == 1 7: if r9 == 0 goto exit: ; mark_ptr_or_null_regs() transfers != 0 info ; for all regs sharing ID: ; (a) r9 != 0 => &frame[0].fp[-32] != 0 ; (b) r9 != 0 => &frame[0].fp[-24] != 0 8: r8 = *r8 ; (a) r8 == &frame[0].fp[-32] ; (b) r8 == &frame[0].fp[-32] 9: r0 = *r8 ; (a) safe ; (b) unsafe exit: 10: exit While processing call to foo() verifier considers the following execution paths: (a) 0-10 (b) 0-4,6-10 (There is also path 0-7,10 but it is not interesting for the issue at hand. (a) is verified first.) Suppose that checkpoint is created at (6) when path (a) is verified, next path (b) is verified and (6) is reached. If states_equal() maintains separate 'idmap' for each frame the mapping at (6) for frame[1] would be empty and regsafe(r9)::check_ids() would add a pair 2->1 and return true, which is an error. If states_equal() maintains single 'idmap' for all frames the mapping at (6) would be { 1->1, 2->2 } and regsafe(r9)::check_ids() would return false when trying to add a pair 2->1. This issue was suggested in the following discussion: https://lore.kernel.org/bpf/CAEf4BzbFB5g4oUfyxk9rHy-PJSLQ3h8q9mV=rVoXfr_JVm8+1Q@mail.gmail.com/ Suggested-by: Andrii Nakryiko Signed-off-by: Eduard Zingerman Link: https://lore.kernel.org/r/20221209135733.28851-4-eddyz87@gmail.com Signed-off-by: Alexei Starovoitov --- include/linux/bpf_verifier.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'include/linux/bpf_verifier.h') diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index df0cb825e0e3..53d175cbaa02 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -273,9 +273,9 @@ struct bpf_id_pair { u32 cur; }; -/* Maximum number of register states that can exist at once */ -#define BPF_ID_MAP_SIZE (MAX_BPF_REG + MAX_BPF_STACK / BPF_REG_SIZE) #define MAX_CALL_FRAMES 8 +/* Maximum number of register states that can exist at once */ +#define BPF_ID_MAP_SIZE ((MAX_BPF_REG + MAX_BPF_STACK / BPF_REG_SIZE) * MAX_CALL_FRAMES) struct bpf_verifier_state { /* call stack tracking */ struct bpf_func_state *frame[MAX_CALL_FRAMES]; -- cgit v1.2.1