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authorGianluca Borello <g.borello@gmail.com>2017-11-22 19:32:56 +0100
committerDaniel Borkmann <daniel@iogearbox.net>2017-11-22 21:40:54 +0100
commita60dd35d2e39209fa7645945e1192bf9769872c6 (patch)
tree1606e891bab8ee8bf102c3f0a3b4319d81a0ef2d /kernel/trace
parentbpf: change bpf_probe_read_str arg2 type to ARG_CONST_SIZE_OR_ZERO (diff)
downloadlinux-a60dd35d2e39209fa7645945e1192bf9769872c6.tar.xz
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bpf: change bpf_perf_event_output arg5 type to ARG_CONST_SIZE_OR_ZERO
Commit 9fd29c08e520 ("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>
Diffstat (limited to 'kernel/trace')
-rw-r--r--kernel/trace/bpf_trace.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index ed8601a1a861..27d1f4ffa3de 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -403,7 +403,7 @@ static const struct bpf_func_proto bpf_perf_event_output_proto = {
.arg2_type = ARG_CONST_MAP_PTR,
.arg3_type = ARG_ANYTHING,
.arg4_type = ARG_PTR_TO_MEM,
- .arg5_type = ARG_CONST_SIZE,
+ .arg5_type = ARG_CONST_SIZE_OR_ZERO,
};
static DEFINE_PER_CPU(struct pt_regs, bpf_pt_regs);
@@ -605,7 +605,7 @@ static const struct bpf_func_proto bpf_perf_event_output_proto_tp = {
.arg2_type = ARG_CONST_MAP_PTR,
.arg3_type = ARG_ANYTHING,
.arg4_type = ARG_PTR_TO_MEM,
- .arg5_type = ARG_CONST_SIZE,
+ .arg5_type = ARG_CONST_SIZE_OR_ZERO,
};
BPF_CALL_3(bpf_get_stackid_tp, void *, tp_buff, struct bpf_map *, map,