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12 commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
Daniel Borkmann
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973377ffe8 |
bpf, selftests: Adjust few selftest outcomes wrt unreachable code
In almost all cases from test_verifier that have been changed in here, we've had an unreachable path with a load from a register which has an invalid address on purpose. This was basically to make sure that we never walk this path and to have the verifier complain if it would otherwise. Change it to match on the right error for unprivileged given we now test these paths under speculative execution. There's one case where we match on exact # of insns_processed. Due to the extra path, this will of course mismatch on unprivileged. Thus, restrict the test->insn_processed check to privileged-only. In one other case, we result in a 'pointer comparison prohibited' error. This is similarly due to verifying an 'invalid' branch where we end up with a value pointer on one side of the comparison. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: John Fastabend <john.fastabend@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> |
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Daniel Borkmann
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d7a5091351 |
bpf: Update selftests to reflect new error states
Update various selftest error messages: * The 'Rx tried to sub from different maps, paths, or prohibited types' is reworked into more specific/differentiated error messages for better guidance. * The change into 'value -4294967168 makes map_value pointer be out of bounds' is due to moving the mixed bounds check into the speculation handling and thus occuring slightly later than above mentioned sanity check. * The change into 'math between map_value pointer and register with unbounded min value' is similarly due to register sanity check coming before the mixed bounds check. * The case of 'map access: known scalar += value_ptr from different maps' now loads fine given masks are the same from the different paths (despite max map value size being different). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: John Fastabend <john.fastabend@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> |
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Jean-Philippe Brucker
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511a76bcb0 |
selftests/bpf: Add test for signed 32-bit bound check bug
After a 32-bit load followed by a branch, the verifier would reduce the maximum bound of the register to 0x7fffffff, allowing a user to bypass bound checks. Ensure such a program is rejected. In the second test, the 64-bit compare should not sufficient to determine whether the signed 32-bit lower bound is 0, so the verifier should reject the second branch. Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org> Acked-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> |
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Yonghong Song
|
f5493c514c |
selftests/bpf: Add verifier tests for xor operation
Added some test_verifier bounds check test cases for xor operations. $ ./test_verifier ... #78/u bounds check for reg = 0, reg xor 1 OK #78/p bounds check for reg = 0, reg xor 1 OK #79/u bounds check for reg32 = 0, reg32 xor 1 OK #79/p bounds check for reg32 = 0, reg32 xor 1 OK #80/u bounds check for reg = 2, reg xor 3 OK #80/p bounds check for reg = 2, reg xor 3 OK #81/u bounds check for reg = any, reg xor 3 OK #81/p bounds check for reg = any, reg xor 3 OK #82/u bounds check for reg32 = any, reg32 xor 3 OK #82/p bounds check for reg32 = any, reg32 xor 3 OK #83/u bounds check for reg > 0, reg xor 3 OK #83/p bounds check for reg > 0, reg xor 3 OK #84/u bounds check for reg32 > 0, reg32 xor 3 OK #84/p bounds check for reg32 > 0, reg32 xor 3 OK ... Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Cc: John Fastabend <john.fastabend@gmail.com> Link: https://lore.kernel.org/bpf/20200825064609.2018077-1-yhs@fb.com |
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Andrii Nakryiko
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457f44363a |
bpf: Implement BPF ring buffer and verifier support for it
This commit adds a new MPSC ring buffer implementation into BPF ecosystem,
which allows multiple CPUs to submit data to a single shared ring buffer. On
the consumption side, only single consumer is assumed.
Motivation
----------
There are two distinctive motivators for this work, which are not satisfied by
existing perf buffer, which prompted creation of a new ring buffer
implementation.
- more efficient memory utilization by sharing ring buffer across CPUs;
- preserving ordering of events that happen sequentially in time, even
across multiple CPUs (e.g., fork/exec/exit events for a task).
These two problems are independent, but perf buffer fails to satisfy both.
Both are a result of a choice to have per-CPU perf ring buffer. Both can be
also solved by having an MPSC implementation of ring buffer. The ordering
problem could technically be solved for perf buffer with some in-kernel
counting, but given the first one requires an MPSC buffer, the same solution
would solve the second problem automatically.
Semantics and APIs
------------------
Single ring buffer is presented to BPF programs as an instance of BPF map of
type BPF_MAP_TYPE_RINGBUF. Two other alternatives considered, but ultimately
rejected.
One way would be to, similar to BPF_MAP_TYPE_PERF_EVENT_ARRAY, make
BPF_MAP_TYPE_RINGBUF could represent an array of ring buffers, but not enforce
"same CPU only" rule. This would be more familiar interface compatible with
existing perf buffer use in BPF, but would fail if application needed more
advanced logic to lookup ring buffer by arbitrary key. HASH_OF_MAPS addresses
this with current approach. Additionally, given the performance of BPF
ringbuf, many use cases would just opt into a simple single ring buffer shared
among all CPUs, for which current approach would be an overkill.
Another approach could introduce a new concept, alongside BPF map, to
represent generic "container" object, which doesn't necessarily have key/value
interface with lookup/update/delete operations. This approach would add a lot
of extra infrastructure that has to be built for observability and verifier
support. It would also add another concept that BPF developers would have to
familiarize themselves with, new syntax in libbpf, etc. But then would really
provide no additional benefits over the approach of using a map.
BPF_MAP_TYPE_RINGBUF doesn't support lookup/update/delete operations, but so
doesn't few other map types (e.g., queue and stack; array doesn't support
delete, etc).
The approach chosen has an advantage of re-using existing BPF map
infrastructure (introspection APIs in kernel, libbpf support, etc), being
familiar concept (no need to teach users a new type of object in BPF program),
and utilizing existing tooling (bpftool). For common scenario of using
a single ring buffer for all CPUs, it's as simple and straightforward, as
would be with a dedicated "container" object. On the other hand, by being
a map, it can be combined with ARRAY_OF_MAPS and HASH_OF_MAPS map-in-maps to
implement a wide variety of topologies, from one ring buffer for each CPU
(e.g., as a replacement for perf buffer use cases), to a complicated
application hashing/sharding of ring buffers (e.g., having a small pool of
ring buffers with hashed task's tgid being a look up key to preserve order,
but reduce contention).
Key and value sizes are enforced to be zero. max_entries is used to specify
the size of ring buffer and has to be a power of 2 value.
There are a bunch of similarities between perf buffer
(BPF_MAP_TYPE_PERF_EVENT_ARRAY) and new BPF ring buffer semantics:
- variable-length records;
- if there is no more space left in ring buffer, reservation fails, no
blocking;
- memory-mappable data area for user-space applications for ease of
consumption and high performance;
- epoll notifications for new incoming data;
- but still the ability to do busy polling for new data to achieve the
lowest latency, if necessary.
BPF ringbuf provides two sets of APIs to BPF programs:
- bpf_ringbuf_output() allows to *copy* data from one place to a ring
buffer, similarly to bpf_perf_event_output();
- bpf_ringbuf_reserve()/bpf_ringbuf_commit()/bpf_ringbuf_discard() APIs
split the whole process into two steps. First, a fixed amount of space is
reserved. If successful, a pointer to a data inside ring buffer data area
is returned, which BPF programs can use similarly to a data inside
array/hash maps. Once ready, this piece of memory is either committed or
discarded. Discard is similar to commit, but makes consumer ignore the
record.
bpf_ringbuf_output() has disadvantage of incurring extra memory copy, because
record has to be prepared in some other place first. But it allows to submit
records of the length that's not known to verifier beforehand. It also closely
matches bpf_perf_event_output(), so will simplify migration significantly.
bpf_ringbuf_reserve() avoids the extra copy of memory by providing a memory
pointer directly to ring buffer memory. In a lot of cases records are larger
than BPF stack space allows, so many programs have use extra per-CPU array as
a temporary heap for preparing sample. bpf_ringbuf_reserve() avoid this needs
completely. But in exchange, it only allows a known constant size of memory to
be reserved, such that verifier can verify that BPF program can't access
memory outside its reserved record space. bpf_ringbuf_output(), while slightly
slower due to extra memory copy, covers some use cases that are not suitable
for bpf_ringbuf_reserve().
The difference between commit and discard is very small. Discard just marks
a record as discarded, and such records are supposed to be ignored by consumer
code. Discard is useful for some advanced use-cases, such as ensuring
all-or-nothing multi-record submission, or emulating temporary malloc()/free()
within single BPF program invocation.
Each reserved record is tracked by verifier through existing
reference-tracking logic, similar to socket ref-tracking. It is thus
impossible to reserve a record, but forget to submit (or discard) it.
bpf_ringbuf_query() helper allows to query various properties of ring buffer.
Currently 4 are supported:
- BPF_RB_AVAIL_DATA returns amount of unconsumed data in ring buffer;
- BPF_RB_RING_SIZE returns the size of ring buffer;
- BPF_RB_CONS_POS/BPF_RB_PROD_POS returns current logical possition of
consumer/producer, respectively.
Returned values are momentarily snapshots of ring buffer state and could be
off by the time helper returns, so this should be used only for
debugging/reporting reasons or for implementing various heuristics, that take
into account highly-changeable nature of some of those characteristics.
One such heuristic might involve more fine-grained control over poll/epoll
notifications about new data availability in ring buffer. Together with
BPF_RB_NO_WAKEUP/BPF_RB_FORCE_WAKEUP flags for output/commit/discard helpers,
it allows BPF program a high degree of control and, e.g., more efficient
batched notifications. Default self-balancing strategy, though, should be
adequate for most applications and will work reliable and efficiently already.
Design and implementation
-------------------------
This reserve/commit schema allows a natural way for multiple producers, either
on different CPUs or even on the same CPU/in the same BPF program, to reserve
independent records and work with them without blocking other producers. This
means that if BPF program was interruped by another BPF program sharing the
same ring buffer, they will both get a record reserved (provided there is
enough space left) and can work with it and submit it independently. This
applies to NMI context as well, except that due to using a spinlock during
reservation, in NMI context, bpf_ringbuf_reserve() might fail to get a lock,
in which case reservation will fail even if ring buffer is not full.
The ring buffer itself internally is implemented as a power-of-2 sized
circular buffer, with two logical and ever-increasing counters (which might
wrap around on 32-bit architectures, that's not a problem):
- consumer counter shows up to which logical position consumer consumed the
data;
- producer counter denotes amount of data reserved by all producers.
Each time a record is reserved, producer that "owns" the record will
successfully advance producer counter. At that point, data is still not yet
ready to be consumed, though. Each record has 8 byte header, which contains
the length of reserved record, as well as two extra bits: busy bit to denote
that record is still being worked on, and discard bit, which might be set at
commit time if record is discarded. In the latter case, consumer is supposed
to skip the record and move on to the next one. Record header also encodes
record's relative offset from the beginning of ring buffer data area (in
pages). This allows bpf_ringbuf_commit()/bpf_ringbuf_discard() to accept only
the pointer to the record itself, without requiring also the pointer to ring
buffer itself. Ring buffer memory location will be restored from record
metadata header. This significantly simplifies verifier, as well as improving
API usability.
Producer counter increments are serialized under spinlock, so there is
a strict ordering between reservations. Commits, on the other hand, are
completely lockless and independent. All records become available to consumer
in the order of reservations, but only after all previous records where
already committed. It is thus possible for slow producers to temporarily hold
off submitted records, that were reserved later.
Reservation/commit/consumer protocol is verified by litmus tests in
Documentation/litmus-test/bpf-rb.
One interesting implementation bit, that significantly simplifies (and thus
speeds up as well) implementation of both producers and consumers is how data
area is mapped twice contiguously back-to-back in the virtual memory. This
allows to not take any special measures for samples that have to wrap around
at the end of the circular buffer data area, because the next page after the
last data page would be first data page again, and thus the sample will still
appear completely contiguous in virtual memory. See comment and a simple ASCII
diagram showing this visually in bpf_ringbuf_area_alloc().
Another feature that distinguishes BPF ringbuf from perf ring buffer is
a self-pacing notifications of new data being availability.
bpf_ringbuf_commit() implementation will send a notification of new record
being available after commit only if consumer has already caught up right up
to the record being committed. If not, consumer still has to catch up and thus
will see new data anyways without needing an extra poll notification.
Benchmarks (see tools/testing/selftests/bpf/benchs/bench_ringbuf.c) show that
this allows to achieve a very high throughput without having to resort to
tricks like "notify only every Nth sample", which are necessary with perf
buffer. For extreme cases, when BPF program wants more manual control of
notifications, commit/discard/output helpers accept BPF_RB_NO_WAKEUP and
BPF_RB_FORCE_WAKEUP flags, which give full control over notifications of data
availability, but require extra caution and diligence in using this API.
Comparison to alternatives
--------------------------
Before considering implementing BPF ring buffer from scratch existing
alternatives in kernel were evaluated, but didn't seem to meet the needs. They
largely fell into few categores:
- per-CPU buffers (perf, ftrace, etc), which don't satisfy two motivations
outlined above (ordering and memory consumption);
- linked list-based implementations; while some were multi-producer designs,
consuming these from user-space would be very complicated and most
probably not performant; memory-mapping contiguous piece of memory is
simpler and more performant for user-space consumers;
- io_uring is SPSC, but also requires fixed-sized elements. Naively turning
SPSC queue into MPSC w/ lock would have subpar performance compared to
locked reserve + lockless commit, as with BPF ring buffer. Fixed sized
elements would be too limiting for BPF programs, given existing BPF
programs heavily rely on variable-sized perf buffer already;
- specialized implementations (like a new printk ring buffer, [0]) with lots
of printk-specific limitations and implications, that didn't seem to fit
well for intended use with BPF programs.
[0] https://lwn.net/Articles/779550/
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200529075424.3139988-2-andriin@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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John Fastabend
|
cf66c29bd7 |
bpf, selftests: Add a verifier test for assigning 32bit reg states to 64bit ones
Added a verifier test for assigning 32bit reg states to 64bit where 32bit reg holds a constant value of 0. Without previous kernel verifier.c fix, the test in this patch will fail. Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/159077335867.6014.2075350327073125374.stgit@john-Precision-5820-Tower |
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John Fastabend
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e3effcdfe0 |
bpf, selftests: Verifier bounds tests need to be updated
After previous fix for zero extension test_verifier tests #65 and #66 now fail. Before the fix we can see the alu32 mov op at insn 10 10: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=invP(id=0, smin_value=4294967168,smax_value=4294967423, umin_value=4294967168,umax_value=4294967423, var_off=(0x0; 0x1ffffffff), s32_min_value=-2147483648,s32_max_value=2147483647, u32_min_value=0,u32_max_value=-1) R10=fp0 fp-8_w=mmmmmmmm 10: (bc) w1 = w1 11: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=invP(id=0, smin_value=0,smax_value=2147483647, umin_value=0,umax_value=4294967295, var_off=(0x0; 0xffffffff), s32_min_value=-2147483648,s32_max_value=2147483647, u32_min_value=0,u32_max_value=-1) R10=fp0 fp-8_w=mmmmmmmm After the fix at insn 10 because we have 's32_min_value < 0' the following step 11 now has 'smax_value=U32_MAX' where before we pulled the s32_max_value bound into the smax_value as seen above in 11 with smax_value=2147483647. 10: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=inv(id=0, smin_value=4294967168,smax_value=4294967423, umin_value=4294967168,umax_value=4294967423, var_off=(0x0; 0x1ffffffff), s32_min_value=-2147483648, s32_max_value=2147483647, u32_min_value=0,u32_max_value=-1) R10=fp0 fp-8_w=mmmmmmmm 10: (bc) w1 = w1 11: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=inv(id=0, smin_value=0,smax_value=4294967295, umin_value=0,umax_value=4294967295, var_off=(0x0; 0xffffffff), s32_min_value=-2147483648, s32_max_value=2147483647, u32_min_value=0, u32_max_value=-1) R10=fp0 fp-8_w=mmmmmmmm The fall out of this is by the time we get to the failing instruction at step 14 where previously we had the following: 14: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=inv(id=0, smin_value=72057594021150720,smax_value=72057594029539328, umin_value=72057594021150720,umax_value=72057594029539328, var_off=(0xffffffff000000; 0xffffff), s32_min_value=-16777216,s32_max_value=-1, u32_min_value=-16777216,u32_max_value=-1) R10=fp0 fp-8_w=mmmmmmmm 14: (0f) r0 += r1 We now have, 14: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=inv(id=0, smin_value=0,smax_value=72057594037927935, umin_value=0,umax_value=72057594037927935, var_off=(0x0; 0xffffffffffffff), s32_min_value=-2147483648,s32_max_value=2147483647, u32_min_value=0,u32_max_value=-1) R10=fp0 fp-8_w=mmmmmmmm 14: (0f) r0 += r1 In the original step 14 'smin_value=72057594021150720' this trips the logic in the verifier function check_reg_sane_offset(), if (smin >= BPF_MAX_VAR_OFF || smin <= -BPF_MAX_VAR_OFF) { verbose(env, "value %lld makes %s pointer be out of bounds\n", smin, reg_type_str[type]); return false; } Specifically, the 'smin <= -BPF_MAX_VAR_OFF' check. But with the fix at step 14 we have bounds 'smin_value=0' so the above check is not tripped because BPF_MAX_VAR_OFF=1<<29. We have a smin_value=0 here because at step 10 the smaller smin_value=0 means the subtractions at steps 11 and 12 bring the smin_value negative. 11: (17) r1 -= 2147483584 12: (17) r1 -= 2147483584 13: (77) r1 >>= 8 Then the shift clears the top bit and smin_value is set to 0. Note we still have the smax_value in the fixed code so any reads will fail. An alternative would be to have reg_sane_check() do both smin and smax value tests. To fix the test we can omit the 'r1 >>=8' at line 13. This will change the err string, but keeps the intention of the test as suggseted by the title, "check after truncation of boundary-crossing range". If the verifier logic changes a different value is likely to be thrown in the error or the error will no longer be thrown forcing this test to be examined. With this change we see the new state at step 13. 13: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=invP(id=0, smin_value=-4294967168,smax_value=127, umin_value=0,umax_value=18446744073709551615, s32_min_value=-2147483648,s32_max_value=2147483647, u32_min_value=0,u32_max_value=-1) R10=fp0 fp-8_w=mmmmmmmm Giving the expected out of bounds error, "value -4294967168 makes map_value pointer be out of bounds" However, for unpriv case we see a different error now because of the mixed signed bounds pointer arithmatic. This seems OK so I've only added the unpriv_errstr for this. Another optino may have been to do addition on r1 instead of subtraction but I favor the approach above slightly. Signed-off-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/159077333942.6014.14004320043595756079.stgit@john-Precision-5820-Tower |
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Colin Ian King
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250e778fe1 |
bpf: Fix spelling mistake "arithmatic" -> "arithmetic" in test_verifier
There are a couple of spelling mistakes in two literal strings, fix them. Signed-off-by: Colin Ian King <colin.king@canonical.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20200331100030.41372-1-colin.king@canonical.com |
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John Fastabend
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41f70fe064 |
bpf: Test_verifier, add alu32 bounds tracking tests
Its possible to have divergent ALU32 and ALU64 bounds when using JMP32 instructins and ALU64 arithmatic operations. Sometimes the clang will even generate this code. Because the case is a bit tricky lets add a specific test for it. Here is pseudocode asm version to illustrate the idea, 1 r0 = 0xffffffff00000001; 2 if w0 > 1 goto %l[fail]; 3 r0 += 1 5 if w0 > 2 goto %l[fail] 6 exit The intent here is the verifier will fail the load if the 32bit bounds are not tracked correctly through ALU64 op. Similarly we can check the 64bit bounds are correctly zero extended after ALU32 ops. 1 r0 = 0xffffffff00000001; 2 w0 += 1 2 if r0 > 3 goto %l[fail]; 6 exit The above will fail if we do not correctly zero extend 64bit bounds after 32bit op. Signed-off-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/158560430155.10843.514209255758200922.stgit@john-Precision-5820-Tower |
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John Fastabend
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32f13a5add |
bpf: Test_verifier, #65 error message updates for trunc of boundary-cross
After changes to add update_reg_bounds after ALU ops and 32-bit bounds
tracking truncation of boundary crossing range will fail earlier and with
a different error message. Now the test error trace is the following
11: (17) r1 -= 2147483584
12: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0)
R1_w=invP(id=0,smin_value=-2147483584,smax_value=63)
R10=fp0 fp-8_w=mmmmmmmm
12: (17) r1 -= 2147483584
13: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0)
R1_w=invP(id=0,
umin_value=18446744069414584448,umax_value=18446744071562068095,
var_off=(0xffffffff00000000; 0xffffffff))
R10=fp0 fp-8_w=mmmmmmmm
13: (77) r1 >>= 8
14: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0)
R1_w=invP(id=0,
umin_value=72057594021150720,umax_value=72057594029539328,
var_off=(0xffffffff000000; 0xffffff),
s32_min_value=-16777216,s32_max_value=-1,
u32_min_value=-16777216)
R10=fp0 fp-8_w=mmmmmmmm
14: (0f) r0 += r1
value 72057594021150720 makes map_value pointer be out of bounds
Because we have 'umin_value == umax_value' instead of previously
where 'umin_value != umax_value' we can now fail earlier noting
that pointer addition is out of bounds.
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/158560428103.10843.6316594510312781186.stgit@john-Precision-5820-Tower
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John Fastabend
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aa131ed44a |
bpf: Test_verifier, #70 error message updates for 32-bit right shift
After changes to add update_reg_bounds after ALU ops and adding ALU32
bounds tracking the error message is changed in the 32-bit right shift
tests.
Test "#70/u bounds check after 32-bit right shift with 64-bit input FAIL"
now fails with,
Unexpected error message!
EXP: R0 invalid mem access
RES: func#0 @0
7: (b7) r1 = 2
8: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=invP2 R10=fp0 fp-8_w=mmmmmmmm
8: (67) r1 <<= 31
9: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=invP4294967296 R10=fp0 fp-8_w=mmmmmmmm
9: (74) w1 >>= 31
10: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=invP0 R10=fp0 fp-8_w=mmmmmmmm
10: (14) w1 -= 2
11: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=invP4294967294 R10=fp0 fp-8_w=mmmmmmmm
11: (0f) r0 += r1
math between map_value pointer and 4294967294 is not allowed
And test "#70/p bounds check after 32-bit right shift with 64-bit input
FAIL" now fails with,
Unexpected error message!
EXP: R0 invalid mem access
RES: func#0 @0
7: (b7) r1 = 2
8: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=inv2 R10=fp0 fp-8_w=mmmmmmmm
8: (67) r1 <<= 31
9: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=inv4294967296 R10=fp0 fp-8_w=mmmmmmmm
9: (74) w1 >>= 31
10: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=inv0 R10=fp0 fp-8_w=mmmmmmmm
10: (14) w1 -= 2
11: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0) R1_w=inv4294967294 R10=fp0 fp-8_w=mmmmmmmm
11: (0f) r0 += r1
last_idx 11 first_idx 0
regs=2 stack=0 before 10: (14) w1 -= 2
regs=2 stack=0 before 9: (74) w1 >>= 31
regs=2 stack=0 before 8: (67) r1 <<= 31
regs=2 stack=0 before 7: (b7) r1 = 2
math between map_value pointer and 4294967294 is not allowed
Before this series we did not trip the "math between map_value pointer..."
error because check_reg_sane_offset is never called in
adjust_ptr_min_max_vals(). Instead we have a register state that looks
like this at line 11*,
11: R0_w=map_value(id=0,off=0,ks=8,vs=8,
smin_value=0,smax_value=0,
umin_value=0,umax_value=0,
var_off=(0x0; 0x0))
R1_w=invP(id=0,
smin_value=0,smax_value=4294967295,
umin_value=0,umax_value=4294967295,
var_off=(0xfffffffe; 0x0))
R10=fp(id=0,off=0,
smin_value=0,smax_value=0,
umin_value=0,umax_value=0,
var_off=(0x0; 0x0)) fp-8_w=mmmmmmmm
11: (0f) r0 += r1
In R1 'smin_val != smax_val' yet we have a tnum_const as seen
by 'var_off(0xfffffffe; 0x0))' with a 0x0 mask. So we hit this check
in adjust_ptr_min_max_vals()
if ((known && (smin_val != smax_val || umin_val != umax_val)) ||
smin_val > smax_val || umin_val > umax_val) {
/* Taint dst register if offset had invalid bounds derived from
* e.g. dead branches.
*/
__mark_reg_unknown(env, dst_reg);
return 0;
}
So we don't throw an error here and instead only throw an error
later in the verification when the memory access is made.
The root cause in verifier without alu32 bounds tracking is having
'umin_value = 0' and 'umax_value = U64_MAX' from BPF_SUB which we set
when 'umin_value < umax_val' here,
if (dst_reg->umin_value < umax_val) {
/* Overflow possible, we know nothing */
dst_reg->umin_value = 0;
dst_reg->umax_value = U64_MAX;
} else { ...}
Later in adjust_calar_min_max_vals we previously did a
coerce_reg_to_size() which will clamp the U64_MAX to U32_MAX by
truncating to 32bits. But either way without a call to update_reg_bounds
the less precise bounds tracking will fall out of the alu op
verification.
After latest changes we now exit adjust_scalar_min_max_vals with the
more precise umin value, due to zero extension propogating bounds from
alu32 bounds into alu64 bounds and then calling update_reg_bounds.
This then causes the verifier to trigger an earlier error and we get
the error in the output above.
This patch updates tests to reflect new error message.
* I have a local patch to print entire verifier state regardless if we
believe it is a constant so we can get a full picture of the state.
Usually if tnum_is_const() then bounds are also smin=smax, etc. but
this is not always true and is a bit subtle. Being able to see these
states helps understand dataflow imo. Let me know if we want something
similar upstream.
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/158507161475.15666.3061518385241144063.stgit@john-Precision-5820-Tower
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Jakub Kicinski
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40f2fbd5a5 |
selftests: bpf: break up test_verifier
Break up the first 10 kLoC of test verifier test cases out into smaller files. Looks like git line counting gets a little flismy above 16 bit integers, so we need two commits to break up test_verifier. Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com> Acked-by: Jiong Wang <jiong.wang@netronome.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> |