bpf: allow access into map value arrays
Suppose you have a map array value that is something like this
struct foo {
unsigned iter;
int array[SOME_CONSTANT];
};
You can easily insert this into an array, but you cannot modify the contents of
foo->array[] after the fact. This is because we have no way to verify we won't
go off the end of the array at verification time. This patch provides a start
for this work. We accomplish this by keeping track of a minimum and maximum
value a register could be while we're checking the code. Then at the time we
try to do an access into a MAP_VALUE we verify that the maximum offset into that
region is a valid access into that memory region. So in practice, code such as
this
unsigned index = 0;
if (foo->iter >= SOME_CONSTANT)
foo->iter = index;
else
index = foo->iter++;
foo->array[index] = bar;
would be allowed, as we can verify that index will always be between 0 and
SOME_CONSTANT-1. If you wish to use signed values you'll have to have an extra
check to make sure the index isn't less than 0, or do something like index %=
SOME_CONSTANT.
Signed-off-by: Josef Bacik <jbacik@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/samples/bpf/libbpf.h b/samples/bpf/libbpf.h
index 364582b..ac6edb6 100644
--- a/samples/bpf/libbpf.h
+++ b/samples/bpf/libbpf.h
@@ -85,6 +85,14 @@
.off = 0, \
.imm = IMM })
+#define BPF_MOV32_IMM(DST, IMM) \
+ ((struct bpf_insn) { \
+ .code = BPF_ALU | BPF_MOV | BPF_K, \
+ .dst_reg = DST, \
+ .src_reg = 0, \
+ .off = 0, \
+ .imm = IMM })
+
/* BPF_LD_IMM64 macro encodes single 'load 64-bit immediate' insn */
#define BPF_LD_IMM64(DST, IMM) \
BPF_LD_IMM64_RAW(DST, 0, IMM)