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bpf: Detect identical PTR_TO_MAP_VALUE_OR_NULL registers

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A BPF program is required to check the return register of a
map_elem_lookup() call before accessing memory. The verifier keeps
track of this by converting the type of the result register from
PTR_TO_MAP_VALUE_OR_NULL to PTR_TO_MAP_VALUE after a conditional
jump ensures safety. This check is currently exclusively performed
for the result register 0.

In the event the compiler reorders instructions, BPF_MOV64_REG
instructions may be moved before the conditional jump which causes
them to keep their type PTR_TO_MAP_VALUE_OR_NULL to which the
verifier objects when the register is accessed:

0: (b7) r1 = 10
1: (7b) *(u64 *)(r10 -8) = r1
2: (bf) r2 = r10
3: (07) r2 += -8
4: (18) r1 = 0x59c00000
6: (85) call 1
7: (bf) r4 = r0
8: (15) if r0 == 0x0 goto pc+1
 R0=map_value(ks=8,vs=8) R4=map_value_or_null(ks=8,vs=8) R10=fp
9: (7a) *(u64 *)(r4 +0) = 0
R4 invalid mem access 'map_value_or_null'

This commit extends the verifier to keep track of all identical
PTR_TO_MAP_VALUE_OR_NULL registers after a map_elem_lookup() by
assigning them an ID and then marking them all when the conditional
jump is observed.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Thomas Graf
2016-10-18 19:51:19 +02:00
committed by David S. Miller
parent 3134e9bdbe
commit 57a09bf0a4
3 changed files with 118 additions and 17 deletions
Download Patch File Download Diff File Expand all files Collapse all files

72
tools/testing/selftests/bpf/test_verifier.c
View File

@@ -2588,6 +2588,78 @@ static struct bpf_test tests[] = {
.result_unpriv = REJECT,
.result = REJECT,
},
{
"multiple registers share map_lookup_elem result",
.insns = {
BPF_MOV64_IMM(BPF_REG_1, 10),
BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
BPF_LD_MAP_FD(BPF_REG_1, 0),
BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
BPF_FUNC_map_lookup_elem),
BPF_MOV64_REG(BPF_REG_4, BPF_REG_0),
BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1),
BPF_ST_MEM(BPF_DW, BPF_REG_4, 0, 0),
BPF_EXIT_INSN(),
},
.fixup_map1 = { 4 },
.result = ACCEPT,
.prog_type = BPF_PROG_TYPE_SCHED_CLS
},
{
"invalid memory access with multiple map_lookup_elem calls",
.insns = {
BPF_MOV64_IMM(BPF_REG_1, 10),
BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
BPF_LD_MAP_FD(BPF_REG_1, 0),
BPF_MOV64_REG(BPF_REG_8, BPF_REG_1),
BPF_MOV64_REG(BPF_REG_7, BPF_REG_2),
BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
BPF_FUNC_map_lookup_elem),
BPF_MOV64_REG(BPF_REG_4, BPF_REG_0),
BPF_MOV64_REG(BPF_REG_1, BPF_REG_8),
BPF_MOV64_REG(BPF_REG_2, BPF_REG_7),
BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
BPF_FUNC_map_lookup_elem),
BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1),
BPF_ST_MEM(BPF_DW, BPF_REG_4, 0, 0),
BPF_EXIT_INSN(),
},
.fixup_map1 = { 4 },
.result = REJECT,
.errstr = "R4 !read_ok",
.prog_type = BPF_PROG_TYPE_SCHED_CLS
},
{
"valid indirect map_lookup_elem access with 2nd lookup in branch",
.insns = {
BPF_MOV64_IMM(BPF_REG_1, 10),
BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
BPF_LD_MAP_FD(BPF_REG_1, 0),
BPF_MOV64_REG(BPF_REG_8, BPF_REG_1),
BPF_MOV64_REG(BPF_REG_7, BPF_REG_2),
BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
BPF_FUNC_map_lookup_elem),
BPF_MOV64_IMM(BPF_REG_2, 10),
BPF_JMP_IMM(BPF_JNE, BPF_REG_2, 0, 3),
BPF_MOV64_REG(BPF_REG_1, BPF_REG_8),
BPF_MOV64_REG(BPF_REG_2, BPF_REG_7),
BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
BPF_FUNC_map_lookup_elem),
BPF_MOV64_REG(BPF_REG_4, BPF_REG_0),
BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1),
BPF_ST_MEM(BPF_DW, BPF_REG_4, 0, 0),
BPF_EXIT_INSN(),
},
.fixup_map1 = { 4 },
.result = ACCEPT,
.prog_type = BPF_PROG_TYPE_SCHED_CLS
},
};
static int probe_filter_length(const struct bpf_insn *fp)