linux/kernel/trace
Gianluca Borello a60dd35d2e bpf: change bpf_perf_event_output arg5 type to ARG_CONST_SIZE_OR_ZERO
Commit 9fd29c08e5 ("bpf: improve verifier ARG_CONST_SIZE_OR_ZERO
semantics") relaxed the treatment of ARG_CONST_SIZE_OR_ZERO due to the way
the compiler generates optimized BPF code when checking boundaries of an
argument from C code. A typical example of this optimized code can be
generated using the bpf_perf_event_output helper when operating on variable
memory:

/* len is a generic scalar */
if (len > 0 && len <= 0x7fff)
        bpf_perf_event_output(ctx, &perf_map, 0, buf, len);

110: (79) r5 = *(u64 *)(r10 -40)
111: (bf) r1 = r5
112: (07) r1 += -1
113: (25) if r1 > 0x7ffe goto pc+6
114: (bf) r1 = r6
115: (18) r2 = 0xffff94e5f166c200
117: (b7) r3 = 0
118: (bf) r4 = r7
119: (85) call bpf_perf_event_output#25
R5 min value is negative, either use unsigned or 'var &= const'

With this code, the verifier loses track of the variable.

Replacing arg5 with ARG_CONST_SIZE_OR_ZERO is thus desirable since it
avoids this quite common case which leads to usability issues, and the
compiler generates code that the verifier can more easily test:

if (len <= 0x7fff)
        bpf_perf_event_output(ctx, &perf_map, 0, buf, len);

or

bpf_perf_event_output(ctx, &perf_map, 0, buf, len & 0x7fff);

No changes to the bpf_perf_event_output helper are necessary since it can
handle a case where size is 0, and an empty frame is pushed.

Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Gianluca Borello <g.borello@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2017-11-22 21:40:54 +01:00
..
Kconfig Tracing updates for 4.15: 2017-11-17 14:58:01 -08:00
Makefile Tracing updates for 4.15: 2017-11-17 14:58:01 -08:00
blktrace.c blktrace: fix unlocked registration of tracepoints 2017-11-10 19:53:25 -07:00
bpf_trace.c bpf: change bpf_perf_event_output arg5 type to ARG_CONST_SIZE_OR_ZERO 2017-11-22 21:40:54 +01:00
ftrace.c Tracing updates for 4.15: 2017-11-17 14:58:01 -08:00
power-traces.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ring_buffer.c Tracing updates for 4.15: 2017-11-17 14:58:01 -08:00
ring_buffer_benchmark.c
rpm-traces.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace.c tracing: Make traceprobe parsing code reusable 2017-10-04 13:06:44 -04:00
trace.h Tracing updates for 4.15: 2017-11-17 14:58:01 -08:00
trace_benchmark.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_benchmark.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_branch.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_clock.c
trace_entries.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_event_perf.c perf/ftrace: Small cleanup 2017-10-16 18:13:28 -04:00
trace_events.c tracing: Reverse the order of trace_types_lock and event_mutex 2017-10-04 11:36:56 -04:00
trace_events_filter.c mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
trace_events_filter_test.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_events_hist.c tracing: Reimplement log2 2017-10-04 13:10:39 -04:00
trace_events_trigger.c
trace_export.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_functions.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_functions_graph.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_hwlat.c
trace_irqsoff.c tracing: Add support for preempt and irq enable/disable events 2017-10-10 18:58:43 -04:00
trace_kdb.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_kprobe.c Tracing updates for 4.15: 2017-11-17 14:58:01 -08:00
trace_mmiotrace.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_nop.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_output.c sched/debug: Rename task-state printing helpers 2017-10-10 11:43:29 +02:00
trace_output.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_printk.c
trace_probe.c tracing: Make traceprobe parsing code reusable 2017-10-04 13:06:44 -04:00
trace_probe.h bpf: Revert bpf_overrid_function() helper changes. 2017-11-11 18:24:55 +09:00
trace_sched_switch.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_sched_wakeup.c Merge branch 'linus' into sched/core, to pick up fixes 2017-11-08 10:17:15 +01:00
trace_selftest.c Tracing updates for 4.15: 2017-11-17 14:58:01 -08:00
trace_selftest_dynamic.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_seq.c
trace_stack.c Merge branch 'linus' into locking/core, to resolve conflicts 2017-11-07 10:32:44 +01:00
trace_stat.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_stat.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_syscalls.c Tracing updates for 4.15: 2017-11-17 14:58:01 -08:00
trace_uprobe.c Tracing updates for 4.15: 2017-11-17 14:58:01 -08:00
tracing_map.c tracing: Remove lookups from tracing_map hitcount 2017-10-04 13:05:42 -04:00
tracing_map.h Tracing updates for 4.15: 2017-11-17 14:58:01 -08:00