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authorDaniel Borkmann <daniel@iogearbox.net>2018-01-18 01:15:21 +0100
committerAlexei Starovoitov <ast@kernel.org>2018-01-17 16:23:17 -0800
commit6f16101e6a8b4324c36e58a29d9e0dbb287cdedb (patch)
tree71777cf318b1d7701d9b014aca031117a8fe42a3 /tools
parentf37a8cb84cce18762e8f86a70bd6a49a66ab964c (diff)
downloadlinux-6f16101e6a8b4324c36e58a29d9e0dbb287cdedb.tar.bz2
bpf: mark dst unknown on inconsistent {s, u}bounds adjustments
syzkaller generated a BPF proglet and triggered a warning with the following: 0: (b7) r0 = 0 1: (d5) if r0 s<= 0x0 goto pc+0 R0=inv0 R1=ctx(id=0,off=0,imm=0) R10=fp0 2: (1f) r0 -= r1 R0=inv0 R1=ctx(id=0,off=0,imm=0) R10=fp0 verifier internal error: known but bad sbounds What happens is that in the first insn, r0's min/max value are both 0 due to the immediate assignment, later in the jsle test the bounds are updated for the min value in the false path, meaning, they yield smin_val = 1, smax_val = 0, and when ctx pointer is subtracted from r0, verifier bails out with the internal error and throwing a WARN since smin_val != smax_val for the known constant. For min_val > max_val scenario it means that reg_set_min_max() and reg_set_min_max_inv() (which both refine existing bounds) demonstrated that such branch cannot be taken at runtime. In above scenario for the case where it will be taken, the existing [0, 0] bounds are kept intact. Meaning, the rejection is not due to a verifier internal error, and therefore the WARN() is not necessary either. We could just reject such cases in adjust_{ptr,scalar}_min_max_vals() when either known scalars have smin_val != smax_val or umin_val != umax_val or any scalar reg with bounds smin_val > smax_val or umin_val > umax_val. However, there may be a small risk of breakage of buggy programs, so handle this more gracefully and in adjust_{ptr,scalar}_min_max_vals() just taint the dst reg as unknown scalar when we see ops with such kind of src reg. Reported-by: syzbot+6d362cadd45dc0a12ba4@syzkaller.appspotmail.com Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'tools')
-rw-r--r--tools/testing/selftests/bpf/test_verifier.c123
1 files changed, 122 insertions, 1 deletions
diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 67e7c41674d2..5ed4175c4ff8 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -6732,7 +6732,7 @@ static struct bpf_test tests[] = {
BPF_JMP_IMM(BPF_JA, 0, 0, -7),
},
.fixup_map1 = { 4 },
- .errstr = "unbounded min value",
+ .errstr = "R0 invalid mem access 'inv'",
.result = REJECT,
},
{
@@ -8634,6 +8634,127 @@ static struct bpf_test tests[] = {
.flags = F_NEEDS_EFFICIENT_UNALIGNED_ACCESS,
},
{
+ "check deducing bounds from const, 1",
+ .insns = {
+ BPF_MOV64_IMM(BPF_REG_0, 1),
+ BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 1, 0),
+ BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1),
+ BPF_EXIT_INSN(),
+ },
+ .result = REJECT,
+ .errstr = "R0 tried to subtract pointer from scalar",
+ },
+ {
+ "check deducing bounds from const, 2",
+ .insns = {
+ BPF_MOV64_IMM(BPF_REG_0, 1),
+ BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 1, 1),
+ BPF_EXIT_INSN(),
+ BPF_JMP_IMM(BPF_JSLE, BPF_REG_0, 1, 1),
+ BPF_EXIT_INSN(),
+ BPF_ALU64_REG(BPF_SUB, BPF_REG_1, BPF_REG_0),
+ BPF_EXIT_INSN(),
+ },
+ .result = ACCEPT,
+ },
+ {
+ "check deducing bounds from const, 3",
+ .insns = {
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_JMP_IMM(BPF_JSLE, BPF_REG_0, 0, 0),
+ BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1),
+ BPF_EXIT_INSN(),
+ },
+ .result = REJECT,
+ .errstr = "R0 tried to subtract pointer from scalar",
+ },
+ {
+ "check deducing bounds from const, 4",
+ .insns = {
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_JMP_IMM(BPF_JSLE, BPF_REG_0, 0, 1),
+ BPF_EXIT_INSN(),
+ BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 1),
+ BPF_EXIT_INSN(),
+ BPF_ALU64_REG(BPF_SUB, BPF_REG_1, BPF_REG_0),
+ BPF_EXIT_INSN(),
+ },
+ .result = ACCEPT,
+ },
+ {
+ "check deducing bounds from const, 5",
+ .insns = {
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 1),
+ BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1),
+ BPF_EXIT_INSN(),
+ },
+ .result = REJECT,
+ .errstr = "R0 tried to subtract pointer from scalar",
+ },
+ {
+ "check deducing bounds from const, 6",
+ .insns = {
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 1),
+ BPF_EXIT_INSN(),
+ BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1),
+ BPF_EXIT_INSN(),
+ },
+ .result = REJECT,
+ .errstr = "R0 tried to subtract pointer from scalar",
+ },
+ {
+ "check deducing bounds from const, 7",
+ .insns = {
+ BPF_MOV64_IMM(BPF_REG_0, ~0),
+ BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 0),
+ BPF_ALU64_REG(BPF_SUB, BPF_REG_1, BPF_REG_0),
+ BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
+ offsetof(struct __sk_buff, mark)),
+ BPF_EXIT_INSN(),
+ },
+ .result = REJECT,
+ .errstr = "dereference of modified ctx ptr",
+ },
+ {
+ "check deducing bounds from const, 8",
+ .insns = {
+ BPF_MOV64_IMM(BPF_REG_0, ~0),
+ BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 1),
+ BPF_ALU64_REG(BPF_ADD, BPF_REG_1, BPF_REG_0),
+ BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
+ offsetof(struct __sk_buff, mark)),
+ BPF_EXIT_INSN(),
+ },
+ .result = REJECT,
+ .errstr = "dereference of modified ctx ptr",
+ },
+ {
+ "check deducing bounds from const, 9",
+ .insns = {
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 0),
+ BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1),
+ BPF_EXIT_INSN(),
+ },
+ .result = REJECT,
+ .errstr = "R0 tried to subtract pointer from scalar",
+ },
+ {
+ "check deducing bounds from const, 10",
+ .insns = {
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_JMP_IMM(BPF_JSLE, BPF_REG_0, 0, 0),
+ /* Marks reg as unknown. */
+ BPF_ALU64_IMM(BPF_NEG, BPF_REG_0, 0),
+ BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1),
+ BPF_EXIT_INSN(),
+ },
+ .result = REJECT,
+ .errstr = "math between ctx pointer and register with unbounded min value is not allowed",
+ },
+ {
"bpf_exit with invalid return code. test1",
.insns = {
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1, 0),