From 2a02759ef5f8a34792df22b41d5e10658fd7bbd3 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Tue, 15 Oct 2019 20:25:02 -0700 Subject: [PATCH] bpf: Add support for BTF pointers to interpreter Pointer to BTF object is a pointer to kernel object or NULL. The memory access in the interpreter has to be done via probe_kernel_read to avoid page faults. Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann Acked-by: Andrii Nakryiko Acked-by: Martin KaFai Lau Link: https://lore.kernel.org/bpf/20191016032505.2089704-9-ast@kernel.org --- include/linux/filter.h | 3 +++ kernel/bpf/core.c | 19 +++++++++++++++++++ kernel/bpf/verifier.c | 8 ++++++++ 3 files changed, 30 insertions(+) diff --git a/include/linux/filter.h b/include/linux/filter.h index d3d51d7aff2c..22ebea2e64ea 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -65,6 +65,9 @@ struct ctl_table_header; /* unused opcode to mark special call to bpf_tail_call() helper */ #define BPF_TAIL_CALL 0xf0 +/* unused opcode to mark special load instruction. Same as BPF_ABS */ +#define BPF_PROBE_MEM 0x20 + /* unused opcode to mark call to interpreter with arguments */ #define BPF_CALL_ARGS 0xe0 diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 66088a9e9b9e..8a765bbd33f0 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -1291,6 +1291,11 @@ bool bpf_opcode_in_insntable(u8 code) } #ifndef CONFIG_BPF_JIT_ALWAYS_ON +u64 __weak bpf_probe_read(void * dst, u32 size, const void * unsafe_ptr) +{ + memset(dst, 0, size); + return -EFAULT; +} /** * __bpf_prog_run - run eBPF program on a given context * @regs: is the array of MAX_BPF_EXT_REG eBPF pseudo-registers @@ -1310,6 +1315,10 @@ static u64 __no_fgcse ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u6 /* Non-UAPI available opcodes. */ [BPF_JMP | BPF_CALL_ARGS] = &&JMP_CALL_ARGS, [BPF_JMP | BPF_TAIL_CALL] = &&JMP_TAIL_CALL, + [BPF_LDX | BPF_PROBE_MEM | BPF_B] = &&LDX_PROBE_MEM_B, + [BPF_LDX | BPF_PROBE_MEM | BPF_H] = &&LDX_PROBE_MEM_H, + [BPF_LDX | BPF_PROBE_MEM | BPF_W] = &&LDX_PROBE_MEM_W, + [BPF_LDX | BPF_PROBE_MEM | BPF_DW] = &&LDX_PROBE_MEM_DW, }; #undef BPF_INSN_3_LBL #undef BPF_INSN_2_LBL @@ -1542,6 +1551,16 @@ static u64 __no_fgcse ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u6 LDST(W, u32) LDST(DW, u64) #undef LDST +#define LDX_PROBE(SIZEOP, SIZE) \ + LDX_PROBE_MEM_##SIZEOP: \ + bpf_probe_read(&DST, SIZE, (const void *)(long) SRC); \ + CONT; + LDX_PROBE(B, 1) + LDX_PROBE(H, 2) + LDX_PROBE(W, 4) + LDX_PROBE(DW, 8) +#undef LDX_PROBE + STX_XADD_W: /* lock xadd *(u32 *)(dst_reg + off16) += src_reg */ atomic_add((u32) SRC, (atomic_t *)(unsigned long) (DST + insn->off)); diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 42a463e09761..c4b6a2cfcd47 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -7581,6 +7581,7 @@ static bool reg_type_mismatch_ok(enum bpf_reg_type type) case PTR_TO_TCP_SOCK: case PTR_TO_TCP_SOCK_OR_NULL: case PTR_TO_XDP_SOCK: + case PTR_TO_BTF_ID: return false; default: return true; @@ -8722,6 +8723,13 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env) case PTR_TO_XDP_SOCK: convert_ctx_access = bpf_xdp_sock_convert_ctx_access; break; + case PTR_TO_BTF_ID: + if (type == BPF_WRITE) { + verbose(env, "Writes through BTF pointers are not allowed\n"); + return -EINVAL; + } + insn->code = BPF_LDX | BPF_PROBE_MEM | BPF_SIZE((insn)->code); + continue; default: continue; }