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Describe BPF helper bpf_map_lookup_elem #5408

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Describe BPF helper bpf_map_lookup_elem #5408

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f5b919f
compiler: support resources in conditional fields
pchaigno Oct 15, 2024
11da221
sys/linux: describe BPF helper bpf_map_lookup_elem
pchaigno Oct 15, 2024
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6 changes: 5 additions & 1 deletion pkg/compiler/check.go
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Original file line number Diff line number Diff line change
Expand Up @@ -649,7 +649,11 @@ func (comp *compiler) checkPathField(target, t *ast.Type, field *ast.Field) bool
}

func (comp *compiler) checkExprLastField(target *ast.Type, field *ast.Field) {
_, desc := comp.derefPointers(field.Type)
typ, desc := comp.derefPointers(field.Type)
if desc == typeResource {
r := comp.resources[typ.Ident]
desc = comp.getTypeDesc(r.Base)
}
if desc != typeInt && desc != typeFlags && desc != typeConst {
comp.error(target.Pos, "%v does not refer to a constant, an integer, or a flag", field.Name.Name)
}
Expand Down
2 changes: 1 addition & 1 deletion pkg/compiler/testdata/errors2.txt
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Expand Up @@ -470,7 +470,7 @@ conditional_fields {
f3 some_nested_flags
f4 int32 (if[value[f3:f1] != 0])
f5 int32 (if[value[f3:f2:f4] != 0]) ### value path f2 does not refer to a struct
f6 int32 (if[value[f3:f4] != 0]) ### f4 does not refer to a constant, an integer, or a flag
f6 int32 (if[value[f3:f4] != 0])
f7 int32 (if[value[f3:some_field] != 0]) ### value target some_field does not exist in some_nested_flags
f8 int32 (if[value[f3:f5] != 0]) ### f5 has conditions, so value path cannot reference it
f9 int32 (if[value[parent:a] != 0]) ### value target a does not exist in conditional_fields
Expand Down
16 changes: 13 additions & 3 deletions prog/expr.go
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Expand Up @@ -46,11 +46,21 @@ func (v *Value) Evaluate(finder ArgFinder) (uint64, bool) {
if found == nil {
panic(fmt.Sprintf("no argument was found by %v", v.Path))
}
constArg, ok := found.(*ConstArg)
if !ok {
val := uint64(0)
iter:
switch arg := found.(type) {
case *ConstArg:
val = arg.Val
case *ResultArg:
if arg.Res != nil {
found = arg.Res
goto iter
}
val = arg.Val
default:
panic("value expressions must only rely on int fields")
}
return constArg.Val, true
return val, true
}

func makeArgFinder(t *Target, c *Call, unionArg *UnionArg, parents parentStack) ArgFinder {
Expand Down
7 changes: 5 additions & 2 deletions sys/linux/bpf.txt
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Expand Up @@ -26,6 +26,7 @@ resource bpf_frozen_const_str[fd_bpf_const_str]
resource tail_call_map_fd[fd_bpf_map]
resource tail_call_map[tail_call_map_fd]
resource ringbuf_map_fd[fd_bpf_map]
resource map_key_size[int32]: 1, 2, 4, 8

# NEED: this is a random index in btf_header:types. We can't express this, so we just use a small index.
type btf_type_id int32[1:5]
Expand Down Expand Up @@ -99,6 +100,8 @@ bpf_map_const_str_freeze {
out bpf_frozen_const_str (out_overlay)
}

syz_create_resource$map_key_size(ksize int32) map_key_size

bpf_map_create_arg [
base bpf_map_create_arg_base
bloom_filter bpf_map_create_arg_bf
Expand Down Expand Up @@ -126,8 +129,8 @@ type bpf_map_create_arg_t[TYPE, KSIZE, VSIZE, MAX, FLAGS, MAP_EXTRA] {
pad2 const[0, int32] (if[value[flags] & BPF_F_TOKEN_FD == 0])
} [packed]

type bpf_map_create_arg_base bpf_map_create_arg_t[flags[bpf_map_type, int32], int32, int32, int32, flags[map_flags, int32], const[0, int64]]
type bpf_map_create_arg_bf bpf_map_create_arg_t[const[BPF_MAP_TYPE_BLOOM_FILTER, int32], int32, int32, int32, flags[map_flags, int32], int64[0:15]]
type bpf_map_create_arg_base bpf_map_create_arg_t[flags[bpf_map_type, int32], map_key_size, int32, int32, flags[map_flags, int32], const[0, int64]]
type bpf_map_create_arg_bf bpf_map_create_arg_t[const[BPF_MAP_TYPE_BLOOM_FILTER, int32], map_key_size, int32, int32, flags[map_flags, int32], int64[0:15]]
type bpf_map_create_arg_ringbuf bpf_map_create_arg_t[const[BPF_MAP_TYPE_RINGBUF, int32], const[0, int32], const[0, int32], int32, const[0, int32], const[0, int64]]
type bpf_map_create_arg_const_str bpf_map_create_arg_t[const[BPF_MAP_TYPE_ARRAY, int32], const[4, int32], const[8, int32], const[1, int32], const[BPF_F_RDONLY_PROG, int32], const[0, int64]]
type bpf_map_create_arg_tail_call bpf_map_create_arg_t[const[BPF_MAP_TYPE_PROG_ARRAY, int32], const[4, int32], const[4, int32], const[10, int32], const[0, int32], const[0, int64]]
Expand Down
27 changes: 27 additions & 0 deletions sys/linux/bpf_prog.txt
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Expand Up @@ -150,6 +150,7 @@ bpf_insn [
tail_call bpf_insn_tail_call
ringbuf_query bpf_insn_ringbuf_query
ringbuf_output bpf_insn_ringbuf_output
map_lookup bpf_insn_map_lookup
] [varlen]

bpf_insn_generic {
Expand All @@ -171,6 +172,9 @@ type bpf_insn_ldst_t[CLASS, SZ, MODE, DST, SRC, OFF, IMM] {
}

type bpf_insn_ldst bpf_insn_ldst_t[bpf_ldst_insn, bpf_ldst_size, bpf_ldst_mode, flags[bpf_reg, int8:4], flags[bpf_reg, int8:4], flags[bpf_insn_offsets, int16], flags[bpf_insn_immediates, int32]]
type bpf_insn_st8_reg[SRC, DST, OFF] bpf_insn_ldst_t[BPF_STX, BPF_B0, BPF_MEM0, const[DST, int8:4], const[SRC, int8:4], const[OFF, int16], const[0, int32]]
type bpf_insn_st16_reg[SRC, DST, OFF] bpf_insn_ldst_t[BPF_STX, BPF_H0, BPF_MEM0, const[DST, int8:4], const[SRC, int8:4], const[OFF, int16], const[0, int32]]
type bpf_insn_st32_reg[SRC, DST, OFF] bpf_insn_ldst_t[BPF_STX, BPF_W0, BPF_MEM0, const[DST, int8:4], const[SRC, int8:4], const[OFF, int16], const[0, int32]]
type bpf_insn_st64_reg[SRC, DST, OFF] bpf_insn_ldst_t[BPF_STX, BPF_DW0, BPF_MEM0, const[DST, int8:4], const[SRC, int8:4], const[OFF, int16], const[0, int32]]

bpf_ldst_insn = BPF_LD, BPF_LDX, BPF_ST, BPF_STX
Expand Down Expand Up @@ -555,3 +559,26 @@ bpf_insn_ringbuf_output {
define MAX_BPF_REG __MAX_BPF_REG

bpf_ringbuf_wakeup_flags = 0, BPF_RB_NO_WAKEUP, BPF_RB_FORCE_WAKEUP

# (18) r1 = map[id:10]
# (b7) r8 = X
# (7b) *(u64 *)(r10 -8) = r8
# (bf) r2 = r10
# (07) r2 -= 8
# (85) call bpf_map_lookup_elem
bpf_insn_map_lookup {
insn1 bpf_insn_map_fd_t[const[BPF_REG_1, int8:4], fd_bpf_map]
insn2 bpf_insn_mov_imm_any[BPF_REG_8]
insn3 bpf_insn_stX_reg
insn4 bpf_insn_mov_reg[BPF_REG_10, BPF_REG_2]
insn5 bpf_insn_alu_t[BPF_ALU64, BPF_K0, BPF_SUB0, const[BPF_REG_2, int8:4], const[0, int8:4], const[0, int16], map_key_size]
insn6 bpf_insn_call_helper_t[const[BPF_FUNC_map_lookup_elem, int32]]
} [packed]

bpf_insn_stX_reg [
st8 bpf_insn_st8_reg[BPF_REG_8, BPF_REG_10, -1] (if[value[parent:parent:insn5:imm] == 1])
st16 bpf_insn_st16_reg[BPF_REG_8, BPF_REG_10, -2] (if[value[parent:parent:insn5:imm] == 2])
st32 bpf_insn_st32_reg[BPF_REG_8, BPF_REG_10, -4] (if[value[parent:parent:insn5:imm] == 4])
st64 bpf_insn_st64_reg[BPF_REG_8, BPF_REG_10, -8] (if[value[parent:parent:insn5:imm] == 8])
fallback bpf_insn_st64_reg[BPF_REG_8, BPF_REG_10, -8]
]
1 change: 1 addition & 0 deletions sys/linux/bpf_prog.txt.const
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Expand Up @@ -43,6 +43,7 @@ BPF_END0 = 13
BPF_EXIT0 = 9
BPF_FLOW_DISSECTOR = 17
BPF_FUNC_INFO_SIZE = 8
BPF_FUNC_map_lookup_elem = 1
BPF_FUNC_ringbuf_discard = 133
BPF_FUNC_ringbuf_output = 130
BPF_FUNC_ringbuf_query = 134
Expand Down
8 changes: 8 additions & 0 deletions sys/linux/test/bpf_helpers_map
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@@ -0,0 +1,8 @@
# Create a BPF map

r0 = syz_create_resource$map_key_size(0x4)
r1 = bpf$MAP_CREATE(AUTO, &AUTO=@base={0x1, r0, 0x8, 0x1, 0x0, 0x0, 0x0, "00000000000000000000000000000000", 0x0, 0x0, 0x0, 0x0, 0x0, AUTO, @void, @value=AUTO, @void, @value=AUTO}, 0x48)

# Lookup an element from the map

r2 = bpf$PROG_LOAD(AUTO, &AUTO={0x3, AUTO, &AUTO=@framed={{AUTO, AUTO, AUTO, AUTO, 0x0, AUTO, AUTO, AUTO, 0x0}, [@map_lookup={{AUTO, AUTO, AUTO, AUTO, r1, AUTO, AUTO, AUTO, AUTO}, {AUTO, AUTO, AUTO, AUTO, AUTO, AUTO, 0x1234}, @st32=AUTO, AUTO, {AUTO, AUTO, AUTO, AUTO, AUTO, AUTO, r0}, AUTO}], AUTO}, &AUTO='GPL\x00', 0x0, 0x0, 0x0, 0x0, 0x0, "00000000000000000000000000000000", 0x0, @sched_cls=0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, @void, @value=AUTO}, 0xa0)
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