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d2102f2f5d
This commit allows progs to elide a null check on statically known map lookup keys. In other words, if the verifier can statically prove that the lookup will be in-bounds, allow the prog to drop the null check. This is useful for two reasons: 1. Large numbers of nullness checks (especially when they cannot fail) unnecessarily pushes prog towards BPF_COMPLEXITY_LIMIT_JMP_SEQ. 2. It forms a tighter contract between programmer and verifier. For (1), bpftrace is starting to make heavier use of percpu scratch maps. As a result, for user scripts with large number of unrolled loops, we are starting to hit jump complexity verification errors. These percpu lookups cannot fail anyways, as we only use static key values. Eliding nullness probably results in less work for verifier as well. For (2), percpu scratch maps are often used as a larger stack, as the currrent stack is limited to 512 bytes. In these situations, it is desirable for the programmer to express: "this lookup should never fail, and if it does, it means I messed up the code". By omitting the null check, the programmer can "ask" the verifier to double check the logic. Tests also have to be updated in sync with these changes, as the verifier is more efficient with this change. Notable, iters.c tests had to be changed to use a map type that still requires null checks, as it's exercising verifier tracking logic w.r.t iterators. Signed-off-by: Daniel Xu <dxu@dxuuu.xyz> Link: https://lore.kernel.org/r/68f3ea96ff3809a87e502a11a4bd30177fc5823e.1736886479.git.dxu@dxuuu.xyz Signed-off-by: Alexei Starovoitov <ast@kernel.org>
143 lines
3.1 KiB
C
143 lines
3.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Converted from tools/testing/selftests/bpf/verifier/map_in_map.c */
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#include <linux/bpf.h>
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#include <bpf/bpf_helpers.h>
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#include "bpf_misc.h"
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struct {
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__uint(type, BPF_MAP_TYPE_ARRAY_OF_MAPS);
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__uint(max_entries, 1);
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__type(key, int);
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__type(value, int);
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__array(values, struct {
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__uint(type, BPF_MAP_TYPE_ARRAY);
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__uint(max_entries, 1);
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__type(key, int);
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__type(value, int);
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});
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} map_in_map SEC(".maps");
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SEC("socket")
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__description("map in map access")
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__success __success_unpriv __retval(0)
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__naked void map_in_map_access(void)
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{
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asm volatile (" \
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r1 = 0; \
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*(u32*)(r10 - 4) = r1; \
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r2 = r10; \
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r2 += -4; \
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r1 = %[map_in_map] ll; \
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call %[bpf_map_lookup_elem]; \
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if r0 == 0 goto l0_%=; \
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r1 = 0; \
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*(u32*)(r10 - 4) = r1; \
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r2 = r10; \
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r2 += -4; \
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r1 = r0; \
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call %[bpf_map_lookup_elem]; \
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l0_%=: r0 = 0; \
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exit; \
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" :
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: __imm(bpf_map_lookup_elem),
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__imm_addr(map_in_map)
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: __clobber_all);
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}
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SEC("xdp")
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__description("map in map state pruning")
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__success __msg("processed 15 insns")
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__log_level(2) __retval(0) __flag(BPF_F_TEST_STATE_FREQ)
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__naked void map_in_map_state_pruning(void)
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{
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asm volatile (" \
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r1 = 0; \
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*(u32*)(r10 - 4) = r1; \
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r6 = r10; \
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r6 += -4; \
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r2 = r6; \
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r1 = %[map_in_map] ll; \
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call %[bpf_map_lookup_elem]; \
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if r0 != 0 goto l0_%=; \
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exit; \
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l0_%=: r2 = r6; \
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r1 = r0; \
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call %[bpf_map_lookup_elem]; \
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if r0 != 0 goto l1_%=; \
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r2 = r6; \
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r1 = %[map_in_map] ll; \
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call %[bpf_map_lookup_elem]; \
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if r0 != 0 goto l2_%=; \
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exit; \
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l2_%=: r2 = r6; \
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r1 = r0; \
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call %[bpf_map_lookup_elem]; \
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if r0 != 0 goto l1_%=; \
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exit; \
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l1_%=: r0 = *(u32*)(r0 + 0); \
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exit; \
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" :
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: __imm(bpf_map_lookup_elem),
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__imm_addr(map_in_map)
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: __clobber_all);
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}
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SEC("socket")
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__description("invalid inner map pointer")
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__failure __msg("R1 pointer arithmetic on map_ptr prohibited")
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__failure_unpriv
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__naked void invalid_inner_map_pointer(void)
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{
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asm volatile (" \
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r1 = 0; \
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*(u32*)(r10 - 4) = r1; \
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r2 = r10; \
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r2 += -4; \
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r1 = %[map_in_map] ll; \
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call %[bpf_map_lookup_elem]; \
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if r0 == 0 goto l0_%=; \
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r1 = 0; \
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*(u32*)(r10 - 4) = r1; \
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r2 = r10; \
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r2 += -4; \
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r1 = r0; \
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r1 += 8; \
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call %[bpf_map_lookup_elem]; \
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l0_%=: r0 = 0; \
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exit; \
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" :
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: __imm(bpf_map_lookup_elem),
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__imm_addr(map_in_map)
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: __clobber_all);
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}
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SEC("socket")
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__description("forgot null checking on the inner map pointer")
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__failure __msg("R1 type=map_value_or_null expected=map_ptr")
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__failure_unpriv
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__naked void on_the_inner_map_pointer(void)
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{
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asm volatile (" \
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r1 = 0; \
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*(u32*)(r10 - 4) = r1; \
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r2 = r10; \
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r2 += -4; \
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r1 = %[map_in_map] ll; \
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call %[bpf_map_lookup_elem]; \
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r1 = 0; \
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*(u32*)(r10 - 4) = r1; \
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r2 = r10; \
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r2 += -4; \
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r1 = r0; \
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call %[bpf_map_lookup_elem]; \
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r0 = 0; \
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exit; \
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" :
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: __imm(bpf_map_lookup_elem),
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__imm_addr(map_in_map)
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: __clobber_all);
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}
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char _license[] SEC("license") = "GPL";
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