* [PATCH net 1/3] bpf: fix incorrect pruning decision when alignment must be tracked
2017-05-23 16:30 [PATCH net 0/3] BPF pruning follow-up Daniel Borkmann
@ 2017-05-23 16:30 ` Daniel Borkmann
2017-05-24 20:07 ` David Miller
2017-05-23 16:30 ` [PATCH net 2/3] bpf: properly reset caller saved regs after helper call and ld_abs/ind Daniel Borkmann
2017-05-23 16:30 ` [PATCH net 3/3] bpf: add various verifier test cases Daniel Borkmann
2 siblings, 1 reply; 6+ messages in thread
From: Daniel Borkmann @ 2017-05-23 16:30 UTC (permalink / raw)
To: davem; +Cc: ast, netdev, Daniel Borkmann
Currently, when we enforce alignment tracking on direct packet access,
the verifier lets the following program pass despite doing a packet
write with unaligned access:
0: (61) r2 = *(u32 *)(r1 +76)
1: (61) r3 = *(u32 *)(r1 +80)
2: (61) r7 = *(u32 *)(r1 +8)
3: (bf) r0 = r2
4: (07) r0 += 14
5: (25) if r7 > 0x1 goto pc+4
R0=pkt(id=0,off=14,r=0) R1=ctx R2=pkt(id=0,off=0,r=0)
R3=pkt_end R7=inv,min_value=0,max_value=1 R10=fp
6: (2d) if r0 > r3 goto pc+1
R0=pkt(id=0,off=14,r=14) R1=ctx R2=pkt(id=0,off=0,r=14)
R3=pkt_end R7=inv,min_value=0,max_value=1 R10=fp
7: (63) *(u32 *)(r0 -4) = r0
8: (b7) r0 = 0
9: (95) exit
from 6 to 8:
R0=pkt(id=0,off=14,r=0) R1=ctx R2=pkt(id=0,off=0,r=0)
R3=pkt_end R7=inv,min_value=0,max_value=1 R10=fp
8: (b7) r0 = 0
9: (95) exit
from 5 to 10:
R0=pkt(id=0,off=14,r=0) R1=ctx R2=pkt(id=0,off=0,r=0)
R3=pkt_end R7=inv,min_value=2 R10=fp
10: (07) r0 += 1
11: (05) goto pc-6
6: safe <----- here, wrongly found safe
processed 15 insns
However, if we enforce a pruning mismatch by adding state into r8
which is then being mismatched in states_equal(), we find that for
the otherwise same program, the verifier detects a misaligned packet
access when actually walking that path:
0: (61) r2 = *(u32 *)(r1 +76)
1: (61) r3 = *(u32 *)(r1 +80)
2: (61) r7 = *(u32 *)(r1 +8)
3: (b7) r8 = 1
4: (bf) r0 = r2
5: (07) r0 += 14
6: (25) if r7 > 0x1 goto pc+4
R0=pkt(id=0,off=14,r=0) R1=ctx R2=pkt(id=0,off=0,r=0)
R3=pkt_end R7=inv,min_value=0,max_value=1
R8=imm1,min_value=1,max_value=1,min_align=1 R10=fp
7: (2d) if r0 > r3 goto pc+1
R0=pkt(id=0,off=14,r=14) R1=ctx R2=pkt(id=0,off=0,r=14)
R3=pkt_end R7=inv,min_value=0,max_value=1
R8=imm1,min_value=1,max_value=1,min_align=1 R10=fp
8: (63) *(u32 *)(r0 -4) = r0
9: (b7) r0 = 0
10: (95) exit
from 7 to 9:
R0=pkt(id=0,off=14,r=0) R1=ctx R2=pkt(id=0,off=0,r=0)
R3=pkt_end R7=inv,min_value=0,max_value=1
R8=imm1,min_value=1,max_value=1,min_align=1 R10=fp
9: (b7) r0 = 0
10: (95) exit
from 6 to 11:
R0=pkt(id=0,off=14,r=0) R1=ctx R2=pkt(id=0,off=0,r=0)
R3=pkt_end R7=inv,min_value=2
R8=imm1,min_value=1,max_value=1,min_align=1 R10=fp
11: (07) r0 += 1
12: (b7) r8 = 0
13: (05) goto pc-7 <----- mismatch due to r8
7: (2d) if r0 > r3 goto pc+1
R0=pkt(id=0,off=15,r=15) R1=ctx R2=pkt(id=0,off=0,r=15)
R3=pkt_end R7=inv,min_value=2
R8=imm0,min_value=0,max_value=0,min_align=2147483648 R10=fp
8: (63) *(u32 *)(r0 -4) = r0
misaligned packet access off 2+15+-4 size 4
The reason why we fail to see it in states_equal() is that the
third test in compare_ptrs_to_packet() ...
if (old->off <= cur->off &&
old->off >= old->range && cur->off >= cur->range)
return true;
... will let the above pass. The situation we run into is that
old->off <= cur->off (14 <= 15), meaning that prior walked paths
went with smaller offset, which was later used in the packet
access after successful packet range check and found to be safe
already.
For example: Given is R0=pkt(id=0,off=0,r=0). Adding offset 14
as in above program to it, results in R0=pkt(id=0,off=14,r=0)
before the packet range test. Now, testing this against R3=pkt_end
with 'if r0 > r3 goto out' will transform R0 into R0=pkt(id=0,off=14,r=14)
for the case when we're within bounds. A write into the packet
at offset *(u32 *)(r0 -4), that is, 2 + 14 -4, is valid and
aligned (2 is for NET_IP_ALIGN). After processing this with
all fall-through paths, we later on check paths from branches.
When the above skb->mark test is true, then we jump near the
end of the program, perform r0 += 1, and jump back to the
'if r0 > r3 goto out' test we've visited earlier already. This
time, R0 is of type R0=pkt(id=0,off=15,r=0), and we'll prune
that part because this time we'll have a larger safe packet
range, and we already found that with off=14 all further insn
were already safe, so it's safe as well with a larger off.
However, the problem is that the subsequent write into the packet
with 2 + 15 -4 is then unaligned, and not caught by the alignment
tracking. Note that min_align, aux_off, and aux_off_align were
all 0 in this example.
Since we cannot tell at this time what kind of packet access was
performed in the prior walk and what minimal requirements it has
(we might do so in the future, but that requires more complexity),
fix it to disable this pruning case for strict alignment for now,
and let the verifier do check such paths instead. With that applied,
the test cases pass and reject the program due to misalignment.
Fixes: d1174416747d ("bpf: Track alignment of register values in the verifier.")
Reference: http://patchwork.ozlabs.org/patch/761909/
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
---
kernel/bpf/verifier.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c72cd41..4fddfe5 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2696,7 +2696,8 @@ static int check_cfg(struct bpf_verifier_env *env)
/* the following conditions reduce the number of explored insns
* from ~140k to ~80k for ultra large programs that use a lot of ptr_to_packet
*/
-static bool compare_ptrs_to_packet(struct bpf_reg_state *old,
+static bool compare_ptrs_to_packet(struct bpf_verifier_env *env,
+ struct bpf_reg_state *old,
struct bpf_reg_state *cur)
{
if (old->id != cur->id)
@@ -2739,7 +2740,7 @@ static bool compare_ptrs_to_packet(struct bpf_reg_state *old,
* 'if (R4 > data_end)' and all further insn were already good with r=20,
* so they will be good with r=30 and we can prune the search.
*/
- if (old->off <= cur->off &&
+ if (!env->strict_alignment && old->off <= cur->off &&
old->off >= old->range && cur->off >= cur->range)
return true;
@@ -2810,7 +2811,7 @@ static bool states_equal(struct bpf_verifier_env *env,
continue;
if (rold->type == PTR_TO_PACKET && rcur->type == PTR_TO_PACKET &&
- compare_ptrs_to_packet(rold, rcur))
+ compare_ptrs_to_packet(env, rold, rcur))
continue;
return false;
--
1.9.3
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH net 3/3] bpf: add various verifier test cases
2017-05-23 16:30 [PATCH net 0/3] BPF pruning follow-up Daniel Borkmann
2017-05-23 16:30 ` [PATCH net 1/3] bpf: fix incorrect pruning decision when alignment must be tracked Daniel Borkmann
2017-05-23 16:30 ` [PATCH net 2/3] bpf: properly reset caller saved regs after helper call and ld_abs/ind Daniel Borkmann
@ 2017-05-23 16:30 ` Daniel Borkmann
2 siblings, 0 replies; 6+ messages in thread
From: Daniel Borkmann @ 2017-05-23 16:30 UTC (permalink / raw)
To: davem; +Cc: ast, netdev, Daniel Borkmann
This patch adds various verifier test cases:
1) A test case for the pruning issue when tracking alignment
is used.
2) Various PTR_TO_MAP_VALUE_OR_NULL tests to make sure pointer
arithmetic turns such register into UNKNOWN_VALUE type.
3) Test cases for the special treatment of LD_ABS/LD_IND to
make sure verifier doesn't break calling convention here.
Latter is needed, since f.e. arm64 JIT uses r1 - r5 for
storing temporary data, so they really must be marked as
NOT_INIT.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
---
include/linux/filter.h | 10 ++
tools/include/linux/filter.h | 10 ++
tools/testing/selftests/bpf/test_verifier.c | 239 +++++++++++++++++++++++++++-
3 files changed, 255 insertions(+), 4 deletions(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 56197f8..62d948f 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -272,6 +272,16 @@
.off = OFF, \
.imm = IMM })
+/* Unconditional jumps, goto pc + off16 */
+
+#define BPF_JMP_A(OFF) \
+ ((struct bpf_insn) { \
+ .code = BPF_JMP | BPF_JA, \
+ .dst_reg = 0, \
+ .src_reg = 0, \
+ .off = OFF, \
+ .imm = 0 })
+
/* Function call */
#define BPF_EMIT_CALL(FUNC) \
diff --git a/tools/include/linux/filter.h b/tools/include/linux/filter.h
index 390d7c9..4ce25d4 100644
--- a/tools/include/linux/filter.h
+++ b/tools/include/linux/filter.h
@@ -208,6 +208,16 @@
.off = OFF, \
.imm = IMM })
+/* Unconditional jumps, goto pc + off16 */
+
+#define BPF_JMP_A(OFF) \
+ ((struct bpf_insn) { \
+ .code = BPF_JMP | BPF_JA, \
+ .dst_reg = 0, \
+ .src_reg = 0, \
+ .off = OFF, \
+ .imm = 0 })
+
/* Function call */
#define BPF_EMIT_CALL(FUNC) \
diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 3773562..cabb19b 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -49,6 +49,7 @@
#define MAX_NR_MAPS 4
#define F_NEEDS_EFFICIENT_UNALIGNED_ACCESS (1 << 0)
+#define F_LOAD_WITH_STRICT_ALIGNMENT (1 << 1)
struct bpf_test {
const char *descr;
@@ -2615,6 +2616,30 @@ struct test_val {
.prog_type = BPF_PROG_TYPE_SCHED_CLS,
},
{
+ "direct packet access: test17 (pruning, alignment)",
+ .insns = {
+ BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,
+ offsetof(struct __sk_buff, data)),
+ BPF_LDX_MEM(BPF_W, BPF_REG_3, BPF_REG_1,
+ offsetof(struct __sk_buff, data_end)),
+ BPF_LDX_MEM(BPF_W, BPF_REG_7, BPF_REG_1,
+ offsetof(struct __sk_buff, mark)),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_2),
+ BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 14),
+ BPF_JMP_IMM(BPF_JGT, BPF_REG_7, 1, 4),
+ BPF_JMP_REG(BPF_JGT, BPF_REG_0, BPF_REG_3, 1),
+ BPF_STX_MEM(BPF_W, BPF_REG_0, BPF_REG_0, -4),
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_EXIT_INSN(),
+ BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 1),
+ BPF_JMP_A(-6),
+ },
+ .errstr = "misaligned packet access off 2+15+-4 size 4",
+ .result = REJECT,
+ .prog_type = BPF_PROG_TYPE_SCHED_CLS,
+ .flags = F_LOAD_WITH_STRICT_ALIGNMENT,
+ },
+ {
"helper access to packet: test1, valid packet_ptr range",
.insns = {
BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,
@@ -3341,6 +3366,70 @@ struct test_val {
.prog_type = BPF_PROG_TYPE_SCHED_CLS
},
{
+ "alu ops on ptr_to_map_value_or_null, 1",
+ .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_ALU64_IMM(BPF_ADD, BPF_REG_4, -2),
+ BPF_ALU64_IMM(BPF_ADD, BPF_REG_4, 2),
+ 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 },
+ .errstr = "R4 invalid mem access",
+ .result = REJECT,
+ .prog_type = BPF_PROG_TYPE_SCHED_CLS
+ },
+ {
+ "alu ops on ptr_to_map_value_or_null, 2",
+ .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_ALU64_IMM(BPF_AND, BPF_REG_4, -1),
+ 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 },
+ .errstr = "R4 invalid mem access",
+ .result = REJECT,
+ .prog_type = BPF_PROG_TYPE_SCHED_CLS
+ },
+ {
+ "alu ops on ptr_to_map_value_or_null, 3",
+ .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_ALU64_IMM(BPF_LSH, BPF_REG_4, 1),
+ 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 },
+ .errstr = "R4 invalid mem access",
+ .result = REJECT,
+ .prog_type = BPF_PROG_TYPE_SCHED_CLS
+ },
+ {
"invalid memory access with multiple map_lookup_elem calls",
.insns = {
BPF_MOV64_IMM(BPF_REG_1, 10),
@@ -4937,7 +5026,149 @@ struct test_val {
.fixup_map_in_map = { 3 },
.errstr = "R1 type=map_value_or_null expected=map_ptr",
.result = REJECT,
- }
+ },
+ {
+ "ld_abs: check calling conv, r1",
+ .insns = {
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+ BPF_MOV64_IMM(BPF_REG_1, 0),
+ BPF_LD_ABS(BPF_W, -0x200000),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_1),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "R1 !read_ok",
+ .result = REJECT,
+ },
+ {
+ "ld_abs: check calling conv, r2",
+ .insns = {
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+ BPF_MOV64_IMM(BPF_REG_2, 0),
+ BPF_LD_ABS(BPF_W, -0x200000),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_2),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "R2 !read_ok",
+ .result = REJECT,
+ },
+ {
+ "ld_abs: check calling conv, r3",
+ .insns = {
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+ BPF_MOV64_IMM(BPF_REG_3, 0),
+ BPF_LD_ABS(BPF_W, -0x200000),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_3),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "R3 !read_ok",
+ .result = REJECT,
+ },
+ {
+ "ld_abs: check calling conv, r4",
+ .insns = {
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+ BPF_MOV64_IMM(BPF_REG_4, 0),
+ BPF_LD_ABS(BPF_W, -0x200000),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_4),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "R4 !read_ok",
+ .result = REJECT,
+ },
+ {
+ "ld_abs: check calling conv, r5",
+ .insns = {
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+ BPF_MOV64_IMM(BPF_REG_5, 0),
+ BPF_LD_ABS(BPF_W, -0x200000),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_5),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "R5 !read_ok",
+ .result = REJECT,
+ },
+ {
+ "ld_abs: check calling conv, r7",
+ .insns = {
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+ BPF_MOV64_IMM(BPF_REG_7, 0),
+ BPF_LD_ABS(BPF_W, -0x200000),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_7),
+ BPF_EXIT_INSN(),
+ },
+ .result = ACCEPT,
+ },
+ {
+ "ld_ind: check calling conv, r1",
+ .insns = {
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+ BPF_MOV64_IMM(BPF_REG_1, 1),
+ BPF_LD_IND(BPF_W, BPF_REG_1, -0x200000),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_1),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "R1 !read_ok",
+ .result = REJECT,
+ },
+ {
+ "ld_ind: check calling conv, r2",
+ .insns = {
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+ BPF_MOV64_IMM(BPF_REG_2, 1),
+ BPF_LD_IND(BPF_W, BPF_REG_2, -0x200000),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_2),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "R2 !read_ok",
+ .result = REJECT,
+ },
+ {
+ "ld_ind: check calling conv, r3",
+ .insns = {
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+ BPF_MOV64_IMM(BPF_REG_3, 1),
+ BPF_LD_IND(BPF_W, BPF_REG_3, -0x200000),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_3),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "R3 !read_ok",
+ .result = REJECT,
+ },
+ {
+ "ld_ind: check calling conv, r4",
+ .insns = {
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+ BPF_MOV64_IMM(BPF_REG_4, 1),
+ BPF_LD_IND(BPF_W, BPF_REG_4, -0x200000),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_4),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "R4 !read_ok",
+ .result = REJECT,
+ },
+ {
+ "ld_ind: check calling conv, r5",
+ .insns = {
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+ BPF_MOV64_IMM(BPF_REG_5, 1),
+ BPF_LD_IND(BPF_W, BPF_REG_5, -0x200000),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_5),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "R5 !read_ok",
+ .result = REJECT,
+ },
+ {
+ "ld_ind: check calling conv, r7",
+ .insns = {
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+ BPF_MOV64_IMM(BPF_REG_7, 1),
+ BPF_LD_IND(BPF_W, BPF_REG_7, -0x200000),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_7),
+ BPF_EXIT_INSN(),
+ },
+ .result = ACCEPT,
+ },
};
static int probe_filter_length(const struct bpf_insn *fp)
@@ -5059,9 +5290,9 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
do_test_fixup(test, prog, map_fds);
- fd_prog = bpf_load_program(prog_type ? : BPF_PROG_TYPE_SOCKET_FILTER,
- prog, prog_len, "GPL", 0, bpf_vlog,
- sizeof(bpf_vlog));
+ fd_prog = bpf_verify_program(prog_type ? : BPF_PROG_TYPE_SOCKET_FILTER,
+ prog, prog_len, test->flags & F_LOAD_WITH_STRICT_ALIGNMENT,
+ "GPL", 0, bpf_vlog, sizeof(bpf_vlog));
expected_ret = unpriv && test->result_unpriv != UNDEF ?
test->result_unpriv : test->result;
--
1.9.3
^ permalink raw reply related [flat|nested] 6+ messages in thread