From 5534e58f2e9bd72b253d033ee0af6e68eb8ac96b Mon Sep 17 00:00:00 2001 From: Ihor Solodrai Date: Mon, 9 Jun 2025 11:30:22 -0700 Subject: [PATCH 1/3] bpf: Make reg_not_null() true for CONST_PTR_TO_MAP When reg->type is CONST_PTR_TO_MAP, it can not be null. However the verifier explores the branches under rX == 0 in check_cond_jmp_op() even if reg->type is CONST_PTR_TO_MAP, because it was not checked for in reg_not_null(). Fix this by adding CONST_PTR_TO_MAP to the set of types that are considered non nullable in reg_not_null(). An old "unpriv: cmp map pointer with zero" selftest fails with this change, because now early out correctly triggers in check_cond_jmp_op(), making the verification to pass. In practice verifier may allow pointer to null comparison in unpriv, since in many cases the relevant branch and comparison op are removed as dead code. So change the expected test result to __success_unpriv. Signed-off-by: Ihor Solodrai Signed-off-by: Andrii Nakryiko Acked-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20250609183024.359974-2-isolodrai@meta.com --- kernel/bpf/verifier.c | 3 ++- tools/testing/selftests/bpf/progs/verifier_unpriv.c | 2 +- 2 files changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index e31f6b0ccb30..48a3241cda0f 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -405,7 +405,8 @@ static bool reg_not_null(const struct bpf_reg_state *reg) type == PTR_TO_MAP_KEY || type == PTR_TO_SOCK_COMMON || (type == PTR_TO_BTF_ID && is_trusted_reg(reg)) || - type == PTR_TO_MEM; + type == PTR_TO_MEM || + type == CONST_PTR_TO_MAP; } static struct btf_record *reg_btf_record(const struct bpf_reg_state *reg) diff --git a/tools/testing/selftests/bpf/progs/verifier_unpriv.c b/tools/testing/selftests/bpf/progs/verifier_unpriv.c index a4a5e2071604..28200f068ce5 100644 --- a/tools/testing/selftests/bpf/progs/verifier_unpriv.c +++ b/tools/testing/selftests/bpf/progs/verifier_unpriv.c @@ -619,7 +619,7 @@ __naked void pass_pointer_to_tail_call(void) SEC("socket") __description("unpriv: cmp map pointer with zero") -__success __failure_unpriv __msg_unpriv("R1 pointer comparison") +__success __success_unpriv __retval(0) __naked void cmp_map_pointer_with_zero(void) { From eb6c99278490a9045662cbc2df9e2a99489df37a Mon Sep 17 00:00:00 2001 From: Ihor Solodrai Date: Mon, 9 Jun 2025 11:30:23 -0700 Subject: [PATCH 2/3] selftests/bpf: Add cmp_map_pointer_with_const test Add a test for CONST_PTR_TO_MAP comparison with a non-0 constant. A BPF program with this code must not pass verification in unpriv. Signed-off-by: Ihor Solodrai Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20250609183024.359974-3-isolodrai@meta.com --- .../selftests/bpf/progs/verifier_unpriv.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/bpf/progs/verifier_unpriv.c b/tools/testing/selftests/bpf/progs/verifier_unpriv.c index 28200f068ce5..db52ba66e880 100644 --- a/tools/testing/selftests/bpf/progs/verifier_unpriv.c +++ b/tools/testing/selftests/bpf/progs/verifier_unpriv.c @@ -624,7 +624,6 @@ __retval(0) __naked void cmp_map_pointer_with_zero(void) { asm volatile (" \ - r1 = 0; \ r1 = %[map_hash_8b] ll; \ if r1 == 0 goto l0_%=; \ l0_%=: r0 = 0; \ @@ -634,6 +633,22 @@ l0_%=: r0 = 0; \ : __clobber_all); } +SEC("socket") +__description("unpriv: cmp map pointer with const") +__success __failure_unpriv __msg_unpriv("R1 pointer comparison prohibited") +__retval(0) +__naked void cmp_map_pointer_with_const(void) +{ + asm volatile (" \ + r1 = %[map_hash_8b] ll; \ + if r1 == 0x0000beef goto l0_%=; \ +l0_%=: r0 = 0; \ + exit; \ +" : + : __imm_addr(map_hash_8b) + : __clobber_all); +} + SEC("socket") __description("unpriv: write into frame pointer") __failure __msg("frame pointer is read only") From 260b8629189611ab5c4894205955b371bed9b75d Mon Sep 17 00:00:00 2001 From: Ihor Solodrai Date: Mon, 9 Jun 2025 11:30:24 -0700 Subject: [PATCH 3/3] selftests/bpf: Add test cases with CONST_PTR_TO_MAP null checks A test requires the following to happen: * CONST_PTR_TO_MAP value is checked for null * the code in the null branch fails verification Add test cases: * direct global map_ptr comparison to null * lookup inner map, then two checks (the first transforms map_value_or_null into map_ptr) * lookup inner map, spill-fill it, then check for null * use an array of ringbufs to recreate a common coding pattern [1] [1] https://lore.kernel.org/bpf/CAEf4BzZNU0gX_sQ8k8JaLe1e+Veth3Rk=4x7MDhv=hQxvO8EDw@mail.gmail.com/ Suggested-by: Andrii Nakryiko Signed-off-by: Ihor Solodrai Signed-off-by: Andrii Nakryiko Acked-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20250609183024.359974-4-isolodrai@meta.com --- .../selftests/bpf/progs/verifier_map_in_map.c | 118 ++++++++++++++++++ 1 file changed, 118 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/verifier_map_in_map.c b/tools/testing/selftests/bpf/progs/verifier_map_in_map.c index 7d088ba99ea5..16b761e510f0 100644 --- a/tools/testing/selftests/bpf/progs/verifier_map_in_map.c +++ b/tools/testing/selftests/bpf/progs/verifier_map_in_map.c @@ -139,4 +139,122 @@ __naked void on_the_inner_map_pointer(void) : __clobber_all); } +SEC("socket") +__description("map_ptr is never null") +__success +__naked void map_ptr_is_never_null(void) +{ + asm volatile (" \ + r0 = 0; \ + r1 = %[map_in_map] ll; \ + if r1 != 0 goto l0_%=; \ + r10 = 42; \ +l0_%=: exit; \ +" : + : __imm(bpf_map_lookup_elem), + __imm_addr(map_in_map) + : __clobber_all); +} + +SEC("socket") +__description("map_ptr is never null inner") +__success +__naked void map_ptr_is_never_null_inner(void) +{ + asm volatile (" \ + r1 = 0; \ + *(u32*)(r10 - 4) = r1; \ + r2 = r10; \ + r2 += -4; \ + r1 = %[map_in_map] ll; \ + call %[bpf_map_lookup_elem]; \ + if r0 == 0 goto l0_%=; \ + if r0 != 0 goto l0_%=; \ + r10 = 42; \ +l0_%=: exit; \ +" : + : __imm(bpf_map_lookup_elem), + __imm_addr(map_in_map) + : __clobber_all); +} + +SEC("socket") +__description("map_ptr is never null inner spill fill") +__success +__naked void map_ptr_is_never_null_inner_spill_fill(void) +{ + asm volatile (" \ + r1 = 0; \ + *(u32*)(r10 - 4) = r1; \ + r2 = r10; \ + r2 += -4; \ + r1 = %[map_in_map] ll; \ + call %[bpf_map_lookup_elem]; \ + if r0 != 0 goto l0_%=; \ + exit; \ +l0_%=: *(u64 *)(r10 -16) = r0; \ + r1 = *(u64 *)(r10 -16); \ + if r1 == 0 goto l1_%=; \ + exit; \ +l1_%=: r10 = 42; \ + exit; \ +" : + : __imm(bpf_map_lookup_elem), + __imm_addr(map_in_map) + : __clobber_all); +} + +struct { + __uint(type, BPF_MAP_TYPE_ARRAY_OF_MAPS); + __uint(max_entries, 1); + __type(key, int); + __type(value, int); + __array(values, struct { + __uint(type, BPF_MAP_TYPE_RINGBUF); + __uint(max_entries, 64 * 1024); + }); +} rb_in_map SEC(".maps"); + +struct rb_ctx { + void *rb; + struct bpf_dynptr dptr; +}; + +static __always_inline struct rb_ctx __rb_event_reserve(__u32 sz) +{ + struct rb_ctx rb_ctx = {}; + void *rb; + __u32 cpu = bpf_get_smp_processor_id(); + __u32 rb_slot = cpu & 1; + + rb = bpf_map_lookup_elem(&rb_in_map, &rb_slot); + if (!rb) + return rb_ctx; + + rb_ctx.rb = rb; + bpf_ringbuf_reserve_dynptr(rb, sz, 0, &rb_ctx.dptr); + + return rb_ctx; +} + +static __noinline void __rb_event_submit(struct rb_ctx *ctx) +{ + if (!ctx->rb) + return; + + /* If the verifier (incorrectly) concludes that ctx->rb can be + * NULL at this point, we'll get "BPF_EXIT instruction in main + * prog would lead to reference leak" error + */ + bpf_ringbuf_submit_dynptr(&ctx->dptr, 0); +} + +SEC("socket") +int map_ptr_is_never_null_rb(void *ctx) +{ + struct rb_ctx event_ctx = __rb_event_reserve(256); + __rb_event_submit(&event_ctx); + return 0; +} + char _license[] SEC("license") = "GPL";