bpf: Add x86-64 JIT support for PROBE_MEM32 pseudo instructions.

Add support for [LDX | STX | ST], PROBE_MEM32, [B | H | W | DW] instructions.
They are similar to PROBE_MEM instructions with the following differences:
- PROBE_MEM has to check that the address is in the kernel range with
  src_reg + insn->off >= TASK_SIZE_MAX + PAGE_SIZE check
- PROBE_MEM doesn't support store
- PROBE_MEM32 relies on the verifier to clear upper 32-bit in the register
- PROBE_MEM32 adds 64-bit kern_vm_start address (which is stored in %r12 in the prologue)
  Due to bpf_arena constructions such %r12 + %reg + off16 access is guaranteed
  to be within arena virtual range, so no address check at run-time.
- PROBE_MEM32 allows STX and ST. If they fault the store is a nop.
  When LDX faults the destination register is zeroed.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/bpf/20240308010812.89848-4-alexei.starovoitov@gmail.com

include/linux/bpf.h

@@ -1458,6 +1458,7 @@ struct bpf_prog_aux {
 	bool xdp_has_frags;
 	bool exception_cb;
 	bool exception_boundary;
+	struct bpf_arena *arena;
 	/* BTF_KIND_FUNC_PROTO for valid attach_btf_id */
 	const struct btf_type *attach_func_proto;
 	/* function name for valid attach_btf_id */

include/linux/filter.h

@@ -72,6 +72,9 @@ struct ctl_table_header;
 /* unused opcode to mark special ldsx instruction. Same as BPF_IND */
 #define BPF_PROBE_MEMSX	0x40
 
+/* unused opcode to mark special load instruction. Same as BPF_MSH */
+#define BPF_PROBE_MEM32	0xa0
+
 /* unused opcode to mark call to interpreter with arguments */
 #define BPF_CALL_ARGS	0xe0