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authorJosef Bacik <jbacik@fb.com>2016-09-28 10:54:32 -0400
committerDavid S. Miller <davem@davemloft.net>2016-09-29 01:35:35 -0400
commit484611357c19f9e19ef742ebef4505a07d243cc9 (patch)
tree34f14c2b2ac71d0bf0a53cab096960e7c91ae87f /samples/bpf/libbpf.h
parent7836667cec5e02ed2ae3eb09b88047b5b5f2343a (diff)
downloadlinux-484611357c19f9e19ef742ebef4505a07d243cc9.tar.bz2
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>
Diffstat (limited to 'samples/bpf/libbpf.h')
-rw-r--r--samples/bpf/libbpf.h8
1 files changed, 8 insertions, 0 deletions
diff --git a/samples/bpf/libbpf.h b/samples/bpf/libbpf.h
index 364582b77888..ac6edb61b64a 100644
--- a/samples/bpf/libbpf.h
+++ b/samples/bpf/libbpf.h
@@ -85,6 +85,14 @@ extern char bpf_log_buf[LOG_BUF_SIZE];
.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)