From 493d9e0d608339a32f568504d5fd411a261bb0af Mon Sep 17 00:00:00 2001 From: Anton Protopopov Date: Wed, 5 Nov 2025 09:04:06 +0000 Subject: bpf, x86: add support for indirect jumps MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Add support for a new instruction BPF_JMP|BPF_X|BPF_JA, SRC=0, DST=Rx, off=0, imm=0 which does an indirect jump to a location stored in Rx. The register Rx should have type PTR_TO_INSN. This new type assures that the Rx register contains a value (or a range of values) loaded from a correct jump table – map of type instruction array. For example, for a C switch LLVM will generate the following code: 0: r3 = r1 # "switch (r3)" 1: if r3 > 0x13 goto +0x666 # check r3 boundaries 2: r3 <<= 0x3 # adjust to an index in array of addresses 3: r1 = 0xbeef ll # r1 is PTR_TO_MAP_VALUE, r1->map_ptr=M 5: r1 += r3 # r1 inherits boundaries from r3 6: r1 = *(u64 *)(r1 + 0x0) # r1 now has type INSN_TO_PTR 7: gotox r1 # jit will generate proper code Here the gotox instruction corresponds to one particular map. This is possible however to have a gotox instruction which can be loaded from different maps, e.g. 0: r1 &= 0x1 1: r2 <<= 0x3 2: r3 = 0x0 ll # load from map M_1 4: r3 += r2 5: if r1 == 0x0 goto +0x4 6: r1 <<= 0x3 7: r3 = 0x0 ll # load from map M_2 9: r3 += r1 A: r1 = *(u64 *)(r3 + 0x0) B: gotox r1 # jump to target loaded from M_1 or M_2 During check_cfg stage the verifier will collect all the maps which point to inside the subprog being verified. When building the config, the high 16 bytes of the insn_state are used, so this patch (theoretically) supports jump tables of up to 2^16 slots. During the later stage, in check_indirect_jump, it is checked that the register Rx was loaded from a particular instruction array. Signed-off-by: Anton Protopopov Acked-by: Eduard Zingerman Link: https://lore.kernel.org/r/20251105090410.1250500-9-a.s.protopopov@gmail.com Signed-off-by: Alexei Starovoitov --- include/linux/bpf.h | 1 + include/linux/bpf_verifier.h | 9 +++++++++ 2 files changed, 10 insertions(+) (limited to 'include') diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 9d41a6affcef..09d5dc541d1c 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1001,6 +1001,7 @@ enum bpf_reg_type { PTR_TO_ARENA, PTR_TO_BUF, /* reg points to a read/write buffer */ PTR_TO_FUNC, /* reg points to a bpf program function */ + PTR_TO_INSN, /* reg points to a bpf program instruction */ CONST_PTR_TO_DYNPTR, /* reg points to a const struct bpf_dynptr */ __BPF_REG_TYPE_MAX, diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 6b820d8d77af..5441341f1ab9 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -527,6 +527,7 @@ struct bpf_insn_aux_data { struct { u32 map_index; /* index into used_maps[] */ u32 map_off; /* offset from value base address */ + struct bpf_iarray *jt; /* jump table for gotox instruction */ }; struct { enum bpf_reg_type reg_type; /* type of pseudo_btf_id */ @@ -840,6 +841,7 @@ struct bpf_verifier_env { struct bpf_scc_info **scc_info; u32 scc_cnt; struct bpf_iarray *succ; + struct bpf_iarray *gotox_tmp_buf; }; static inline struct bpf_func_info_aux *subprog_aux(struct bpf_verifier_env *env, int subprog) @@ -1050,6 +1052,13 @@ static inline bool bpf_stack_narrow_access_ok(int off, int fill_size, int spill_ return !(off % BPF_REG_SIZE); } +static inline bool insn_is_gotox(struct bpf_insn *insn) +{ + return BPF_CLASS(insn->code) == BPF_JMP && + BPF_OP(insn->code) == BPF_JA && + BPF_SRC(insn->code) == BPF_X; +} + const char *reg_type_str(struct bpf_verifier_env *env, enum bpf_reg_type type); const char *dynptr_type_str(enum bpf_dynptr_type type); const char *iter_type_str(const struct btf *btf, u32 btf_id); -- cgit v1.2.3