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selftests/bpf: Verify that check_ids() is used for scalars in regsafe()
Verify that the following example is rejected by verifier: r9 = ... some pointer with range X ... r6 = ... unbound scalar ID=a ... r7 = ... unbound scalar ID=b ... if (r6 > r7) goto +1 r7 = r6 if (r7 > X) goto exit r9 += r6 *(u64 *)r9 = Y Also add test cases to: - check that check_alu_op() for BPF_MOV instruction does not allocate scalar ID if source register is a constant; - check that unique scalar IDs are ignored when new verifier state is compared to cached verifier state; - check that two different scalar IDs in a verified state can't be mapped to the same scalar ID in current state. Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20230613153824.3324830-5-eddyz87@gmail.com
This commit is contained in:
Eduard Zingerman
Andrii Nakryiko
parent
1ffc85d929
commit
18b8926557
1 changed files with 315 additions and 0 deletions
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@ -341,4 +341,319 @@ __naked void precision_two_ids(void)
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: __clobber_all);
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}
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/* Verify that check_ids() is used by regsafe() for scalars.
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*
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* r9 = ... some pointer with range X ...
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* r6 = ... unbound scalar ID=a ...
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* r7 = ... unbound scalar ID=b ...
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* if (r6 > r7) goto +1
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* r7 = r6
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* if (r7 > X) goto exit
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* r9 += r6
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* ... access memory using r9 ...
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*
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* The memory access is safe only if r7 is bounded,
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* which is true for one branch and not true for another.
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*/
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SEC("socket")
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__failure __msg("register with unbounded min value")
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__flag(BPF_F_TEST_STATE_FREQ)
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__naked void check_ids_in_regsafe(void)
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{
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asm volatile (
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/* Bump allocated stack */
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"r1 = 0;"
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"*(u64*)(r10 - 8) = r1;"
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/* r9 = pointer to stack */
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"r9 = r10;"
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"r9 += -8;"
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/* r7 = ktime_get_ns() */
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"call %[bpf_ktime_get_ns];"
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"r7 = r0;"
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/* r6 = ktime_get_ns() */
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"call %[bpf_ktime_get_ns];"
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"r6 = r0;"
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/* if r6 > r7 is an unpredictable jump */
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"if r6 > r7 goto l1_%=;"
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"r7 = r6;"
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"l1_%=:"
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/* if r7 > 4 ...; transfers range to r6 on one execution path
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* but does not transfer on another
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*/
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"if r7 > 4 goto l2_%=;"
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/* Access memory at r9[r6], r6 is not always bounded */
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"r9 += r6;"
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"r0 = *(u8*)(r9 + 0);"
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"l2_%=:"
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"r0 = 0;"
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"exit;"
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:
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: __imm(bpf_ktime_get_ns)
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: __clobber_all);
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}
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/* Similar to check_ids_in_regsafe.
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* The l0 could be reached in two states:
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*
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* (1) r6{.id=A}, r7{.id=A}, r8{.id=B}
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* (2) r6{.id=B}, r7{.id=A}, r8{.id=B}
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*
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* Where (2) is not safe, as "r7 > 4" check won't propagate range for it.
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* This example would be considered safe without changes to
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* mark_chain_precision() to track scalar values with equal IDs.
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*/
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SEC("socket")
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__failure __msg("register with unbounded min value")
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__flag(BPF_F_TEST_STATE_FREQ)
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__naked void check_ids_in_regsafe_2(void)
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{
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asm volatile (
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/* Bump allocated stack */
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"r1 = 0;"
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"*(u64*)(r10 - 8) = r1;"
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/* r9 = pointer to stack */
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"r9 = r10;"
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"r9 += -8;"
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/* r8 = ktime_get_ns() */
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"call %[bpf_ktime_get_ns];"
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"r8 = r0;"
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/* r7 = ktime_get_ns() */
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"call %[bpf_ktime_get_ns];"
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"r7 = r0;"
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/* r6 = ktime_get_ns() */
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"call %[bpf_ktime_get_ns];"
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"r6 = r0;"
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/* scratch .id from r0 */
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"r0 = 0;"
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/* if r6 > r7 is an unpredictable jump */
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"if r6 > r7 goto l1_%=;"
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/* tie r6 and r7 .id */
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"r6 = r7;"
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"l0_%=:"
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/* if r7 > 4 exit(0) */
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"if r7 > 4 goto l2_%=;"
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/* Access memory at r9[r6] */
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"r9 += r6;"
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"r0 = *(u8*)(r9 + 0);"
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"l2_%=:"
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"r0 = 0;"
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"exit;"
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"l1_%=:"
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/* tie r6 and r8 .id */
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"r6 = r8;"
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"goto l0_%=;"
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:
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: __imm(bpf_ktime_get_ns)
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: __clobber_all);
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}
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/* Check that scalar IDs *are not* generated on register to register
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* assignments if source register is a constant.
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*
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* If such IDs *are* generated the 'l1' below would be reached in
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* two states:
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*
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* (1) r1{.id=A}, r2{.id=A}
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* (2) r1{.id=C}, r2{.id=C}
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*
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* Thus forcing 'if r1 == r2' verification twice.
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*/
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SEC("socket")
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__success __log_level(2)
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__msg("11: (1d) if r3 == r4 goto pc+0")
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__msg("frame 0: propagating r3,r4")
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__msg("11: safe")
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__msg("processed 15 insns")
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__flag(BPF_F_TEST_STATE_FREQ)
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__naked void no_scalar_id_for_const(void)
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{
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asm volatile (
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"call %[bpf_ktime_get_ns];"
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/* unpredictable jump */
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"if r0 > 7 goto l0_%=;"
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/* possibly generate same scalar ids for r3 and r4 */
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"r1 = 0;"
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"r1 = r1;"
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"r3 = r1;"
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"r4 = r1;"
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"goto l1_%=;"
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"l0_%=:"
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/* possibly generate different scalar ids for r3 and r4 */
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"r1 = 0;"
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"r2 = 0;"
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"r3 = r1;"
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"r4 = r2;"
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"l1_%=:"
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/* predictable jump, marks r3 and r4 precise */
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"if r3 == r4 goto +0;"
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"r0 = 0;"
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"exit;"
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:
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: __imm(bpf_ktime_get_ns)
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: __clobber_all);
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}
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/* Same as no_scalar_id_for_const() but for 32-bit values */
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SEC("socket")
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__success __log_level(2)
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__msg("11: (1e) if w3 == w4 goto pc+0")
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__msg("frame 0: propagating r3,r4")
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__msg("11: safe")
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__msg("processed 15 insns")
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__flag(BPF_F_TEST_STATE_FREQ)
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__naked void no_scalar_id_for_const32(void)
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{
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asm volatile (
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"call %[bpf_ktime_get_ns];"
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/* unpredictable jump */
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"if r0 > 7 goto l0_%=;"
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/* possibly generate same scalar ids for r3 and r4 */
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"w1 = 0;"
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"w1 = w1;"
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"w3 = w1;"
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"w4 = w1;"
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"goto l1_%=;"
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"l0_%=:"
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/* possibly generate different scalar ids for r3 and r4 */
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"w1 = 0;"
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"w2 = 0;"
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"w3 = w1;"
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"w4 = w2;"
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"l1_%=:"
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/* predictable jump, marks r1 and r2 precise */
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"if w3 == w4 goto +0;"
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"r0 = 0;"
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"exit;"
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:
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: __imm(bpf_ktime_get_ns)
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: __clobber_all);
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}
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/* Check that unique scalar IDs are ignored when new verifier state is
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* compared to cached verifier state. For this test:
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* - cached state has no id on r1
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* - new state has a unique id on r1
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*/
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SEC("socket")
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__success __log_level(2)
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__msg("6: (25) if r6 > 0x7 goto pc+1")
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__msg("7: (57) r1 &= 255")
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__msg("8: (bf) r2 = r10")
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__msg("from 6 to 8: safe")
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__msg("processed 12 insns")
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__flag(BPF_F_TEST_STATE_FREQ)
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__naked void ignore_unique_scalar_ids_cur(void)
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{
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asm volatile (
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"call %[bpf_ktime_get_ns];"
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"r6 = r0;"
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"call %[bpf_ktime_get_ns];"
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"r0 &= 0xff;"
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/* r1.id == r0.id */
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"r1 = r0;"
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/* make r1.id unique */
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"r0 = 0;"
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"if r6 > 7 goto l0_%=;"
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/* clear r1 id, but keep the range compatible */
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"r1 &= 0xff;"
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"l0_%=:"
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/* get here in two states:
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* - first: r1 has no id (cached state)
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* - second: r1 has a unique id (should be considered equivalent)
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*/
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"r2 = r10;"
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"r2 += r1;"
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"exit;"
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:
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: __imm(bpf_ktime_get_ns)
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: __clobber_all);
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}
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/* Check that unique scalar IDs are ignored when new verifier state is
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* compared to cached verifier state. For this test:
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* - cached state has a unique id on r1
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* - new state has no id on r1
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*/
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SEC("socket")
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__success __log_level(2)
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__msg("6: (25) if r6 > 0x7 goto pc+1")
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__msg("7: (05) goto pc+1")
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__msg("9: (bf) r2 = r10")
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__msg("9: safe")
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__msg("processed 13 insns")
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__flag(BPF_F_TEST_STATE_FREQ)
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__naked void ignore_unique_scalar_ids_old(void)
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{
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asm volatile (
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"call %[bpf_ktime_get_ns];"
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"r6 = r0;"
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"call %[bpf_ktime_get_ns];"
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"r0 &= 0xff;"
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/* r1.id == r0.id */
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"r1 = r0;"
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/* make r1.id unique */
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"r0 = 0;"
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"if r6 > 7 goto l1_%=;"
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"goto l0_%=;"
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"l1_%=:"
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/* clear r1 id, but keep the range compatible */
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"r1 &= 0xff;"
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"l0_%=:"
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/* get here in two states:
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* - first: r1 has a unique id (cached state)
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* - second: r1 has no id (should be considered equivalent)
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*/
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"r2 = r10;"
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"r2 += r1;"
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"exit;"
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:
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: __imm(bpf_ktime_get_ns)
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: __clobber_all);
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}
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/* Check that two different scalar IDs in a verified state can't be
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* mapped to the same scalar ID in current state.
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*/
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SEC("socket")
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__success __log_level(2)
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/* The exit instruction should be reachable from two states,
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* use two matches and "processed .. insns" to ensure this.
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*/
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__msg("13: (95) exit")
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__msg("13: (95) exit")
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__msg("processed 18 insns")
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__flag(BPF_F_TEST_STATE_FREQ)
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__naked void two_old_ids_one_cur_id(void)
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{
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asm volatile (
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/* Give unique scalar IDs to r{6,7} */
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"call %[bpf_ktime_get_ns];"
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"r0 &= 0xff;"
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"r6 = r0;"
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"call %[bpf_ktime_get_ns];"
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"r0 &= 0xff;"
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"r7 = r0;"
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"r0 = 0;"
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/* Maybe make r{6,7} IDs identical */
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"if r6 > r7 goto l0_%=;"
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"goto l1_%=;"
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"l0_%=:"
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"r6 = r7;"
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"l1_%=:"
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/* Mark r{6,7} precise.
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* Get here in two states:
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* - first: r6{.id=A}, r7{.id=B} (cached state)
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* - second: r6{.id=A}, r7{.id=A}
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* Currently we don't want to consider such states equivalent.
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* Thus "exit;" would be verified twice.
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*/
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"r2 = r10;"
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"r2 += r6;"
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"r2 += r7;"
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"exit;"
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:
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: __imm(bpf_ktime_get_ns)
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: __clobber_all);
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}
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char _license[] SEC("license") = "GPL";
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