bpf, x86: add new map type: instructions array

On bpf(BPF_PROG_LOAD) syscall user-supplied BPF programs are
translated by the verifier into "xlated" BPF programs. During this
process the original instructions offsets might be adjusted and/or
individual instructions might be replaced by new sets of instructions,
or deleted.

Add a new BPF map type which is aimed to keep track of how, for a
given program, the original instructions were relocated during the
verification. Also, besides keeping track of the original -> xlated
mapping, make x86 JIT to build the xlated -> jitted mapping for every
instruction listed in an instruction array. This is required for every
future application of instruction arrays: static keys, indirect jumps
and indirect calls.

A map of the BPF_MAP_TYPE_INSN_ARRAY type must be created with a u32
keys and value of size 8. The values have different semantics for
userspace and for BPF space. For userspace a value consists of two
u32 values – xlated and jitted offsets. For BPF side the value is
a real pointer to a jitted instruction.

On map creation/initialization, before loading the program, each
element of the map should be initialized to point to an instruction
offset within the program. Before the program load such maps should
be made frozen. After the program verification xlated and jitted
offsets can be read via the bpf(2) syscall.

If a tracked instruction is removed by the verifier, then the xlated
offset is set to (u32)-1 which is considered to be too big for a valid
BPF program offset.

One such a map can, obviously, be used to track one and only one BPF
program.  If the verification process was unsuccessful, then the same
map can be re-used to verify the program with a different log level.
However, if the program was loaded fine, then such a map, being
frozen in any case, can't be reused by other programs even after the
program release.

Example. Consider the following original and xlated programs:

    Original prog:                      Xlated prog:

     0:  r1 = 0x0                        0: r1 = 0
     1:  *(u32 *)(r10 - 0x4) = r1        1: *(u32 *)(r10 -4) = r1
     2:  r2 = r10                        2: r2 = r10
     3:  r2 += -0x4                      3: r2 += -4
     4:  r1 = 0x0 ll                     4: r1 = map[id:88]
     6:  call 0x1                        6: r1 += 272
                                         7: r0 = *(u32 *)(r2 +0)
                                         8: if r0 >= 0x1 goto pc+3
                                         9: r0 <<= 3
                                        10: r0 += r1
                                        11: goto pc+1
                                        12: r0 = 0
     7:  r6 = r0                        13: r6 = r0
     8:  if r6 == 0x0 goto +0x2         14: if r6 == 0x0 goto pc+4
     9:  call 0x76                      15: r0 = 0xffffffff8d2079c0
                                        17: r0 = *(u64 *)(r0 +0)
    10:  *(u64 *)(r6 + 0x0) = r0        18: *(u64 *)(r6 +0) = r0
    11:  r0 = 0x0                       19: r0 = 0x0
    12:  exit                           20: exit

An instruction array map, containing, e.g., instructions [0,4,7,12]
will be translated by the verifier to [0,4,13,20]. A map with
index 5 (the middle of 16-byte instruction) or indexes greater than 12
(outside the program boundaries) would be rejected.

The functionality provided by this patch will be extended in consequent
patches to implement BPF Static Keys, indirect jumps, and indirect calls.

Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20251105090410.1250500-2-a.s.protopopov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 8a129746bd6c..f62d61b6730a 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1493,6 +1493,7 @@ static int map_create(union bpf_attr *attr, bpfptr_t uattr)
 	case BPF_MAP_TYPE_STRUCT_OPS:
 	case BPF_MAP_TYPE_CPUMAP:
 	case BPF_MAP_TYPE_ARENA:
+	case BPF_MAP_TYPE_INSN_ARRAY:
 		if (!bpf_token_capable(token, CAP_BPF))
 			goto put_token;
 		break;
@@ -2853,6 +2854,23 @@ static int bpf_prog_verify_signature(struct bpf_prog *prog, union bpf_attr *attr
 	return err;
 }
 
+static int bpf_prog_mark_insn_arrays_ready(struct bpf_prog *prog)
+{
+	int err;
+	int i;
+
+	for (i = 0; i < prog->aux->used_map_cnt; i++) {
+		if (prog->aux->used_maps[i]->map_type != BPF_MAP_TYPE_INSN_ARRAY)
+			continue;
+
+		err = bpf_insn_array_ready(prog->aux->used_maps[i]);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
 /* last field in 'union bpf_attr' used by this command */
 #define BPF_PROG_LOAD_LAST_FIELD keyring_id
 
@@ -3082,6 +3100,10 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
 	if (err < 0)
 		goto free_used_maps;
 
+	err = bpf_prog_mark_insn_arrays_ready(prog);
+	if (err < 0)
+		goto free_used_maps;
+
 	err = bpf_prog_alloc_id(prog);
 	if (err)
 		goto free_used_maps;