From: Andrii Nakryiko andrii@kernel.org
[ Upstream commit 879bbe7aa4afa80acf72a1cad7f52416ea78c52d ]
For program types that don't have named context type name (e.g., BPF iterator programs or tracepoint programs), ctx_tname will be a non-NULL empty string. For such programs it shouldn't be possible to have PTR_TO_CTX argument for global subprogs based on type name alone. arg:ctx tag is the only way to have PTR_TO_CTX passed into global subprog for such program types.
Fix this loophole, which currently would assume PTR_TO_CTX whenever user uses a pointer to anonymous struct as an argument to their global subprogs. This happens in practice with the following (quite common, in practice) approach:
typedef struct { /* anonymous */ int x; } my_type_t;
int my_subprog(my_type_t *arg) { ... }
User's intent is to have PTR_TO_MEM argument for `arg`, but verifier will complain about expecting PTR_TO_CTX.
This fix also closes unintended s390x-specific KPROBE handling of PTR_TO_CTX case. Selftest change is necessary to accommodate this.
Fixes: 91cc1a99740e ("bpf: Annotate context types") Signed-off-by: Andrii Nakryiko andrii@kernel.org Link: https://lore.kernel.org/r/20240212233221.2575350-4-andrii@kernel.org Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/btf.c | 3 +++ .../bpf/progs/test_global_func_ctx_args.c | 19 +++++++++++++++++++ 2 files changed, 22 insertions(+)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index a31704a6bb614..9445ae6a280e6 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -5655,6 +5655,9 @@ btf_get_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf, bpf_log(log, "Please fix kernel include/linux/bpf_types.h\n"); return NULL; } + /* program types without named context types work only with arg:ctx tag */ + if (ctx_tname[0] == '\0') + return false; /* only compare that prog's ctx type name is the same as * kernel expects. No need to compare field by field. * It's ok for bpf prog to do: diff --git a/tools/testing/selftests/bpf/progs/test_global_func_ctx_args.c b/tools/testing/selftests/bpf/progs/test_global_func_ctx_args.c index 7faa8eef0598b..144d30e654ad2 100644 --- a/tools/testing/selftests/bpf/progs/test_global_func_ctx_args.c +++ b/tools/testing/selftests/bpf/progs/test_global_func_ctx_args.c @@ -26,6 +26,23 @@ int kprobe_typedef_ctx(void *ctx) return kprobe_typedef_ctx_subprog(ctx); }
+/* s390x defines: + * + * typedef user_pt_regs bpf_user_pt_regs_t; + * typedef struct { ... } user_pt_regs; + * + * And so "canonical" underlying struct type is anonymous. + * So on s390x only valid ways to have PTR_TO_CTX argument in global subprogs + * are: + * - bpf_user_pt_regs_t *ctx (typedef); + * - struct bpf_user_pt_regs_t *ctx (backwards compatible struct hack); + * - void *ctx __arg_ctx (arg:ctx tag) + * + * Other architectures also allow using underlying struct types (e.g., + * `struct pt_regs *ctx` for x86-64) + */ +#ifndef bpf_target_s390 + #define pt_regs_struct_t typeof(*(__PT_REGS_CAST((struct pt_regs *)NULL)))
__weak int kprobe_struct_ctx_subprog(pt_regs_struct_t *ctx) @@ -40,6 +57,8 @@ int kprobe_resolved_ctx(void *ctx) return kprobe_struct_ctx_subprog(ctx); }
+#endif + /* this is current hack to make this work on old kernels */ struct bpf_user_pt_regs_t {};